by dr nasser al-daghri1 444 bchimmunology by nasser m. al-daghri, ph.d assistant professor college...

By Dr Nasser AL-DAGHRI 1

444 BCH

ImmunologyImmunologyBY

Nasser M. Al-Daghri, Ph.DNasser M. Al-Daghri, Ph.DAssistant Professor

College of Science Biochemistry Department

King Saud University


Self or non-self

The body must be able to distinguish between self (or which is identical to self) and non self (or foreign).

It is also important to distinguish threatening from non threatening

Organisms must interact with environment to recognize and respond to external and internal threats to increase the opportunity for survival and production


The immunological concept of self

A quick glance in the mirror each morning gives us visual cues assuring us, that indeed it is our self staring back at us.

Strangers may require the presentation of some type of document (photograph) to ensure that we are who we say we are and that we belong where we are and belong where we are.

Individual can be distinguished by gender, face, shape


Continuation… When the immune system encounters cells or

molecules, it must determine for us whether they belong to the body – whether it’s self or non self. This decision is made without the benefit of such visual clues.

The immune system uses variety of soluble molecules and cell bound surface receptors to determine whether the molecules that it encounters are self or non self.

The need to distinguish self and non self and to encounter threats from non self has been met in different ways.


Continuation… The need to distinguish self and non self and to

encounter threats from non self has been met in different ways: These include detriments of physical or chemical barriers to present the entry of external designed to detect and distinguish self and non self and special cell and molecules that destroy and remove materials indentical as non self

Some immune system, as in humans, have also developed the ability to identify and recall threat previously encountered (immunological memory)

And like many biological systems the immune system plays raindancay- multiple mechanisms with overlapping function to ensure that one mechanism is not effective on other may be.


ImmunityImmunity

Protection from harmful microorganisms (bacteria, Protection from harmful microorganisms (bacteria, viruses, fungi and parasites)viruses, fungi and parasites)

ImmunityImmunity

INNATEINNATE

ADAPTIVEADAPTIVE


Innate immunity

(e.g., macrophages, neutrophils, certain molecules) is the first line of defense. It is fast (usually good-to-go) and usually effective.

Adaptive immunity

(mediated by B and T cells) can be slow to respond (several days). It is highly effective when the innate immune system cannot fully deal with the threat.

Principles of innate and adaptive immunity


Roles of the Immune SystemRoles of the Immune System

• Defense Against InfectionDefense Against Infection

• Surveillance for MalignancySurveillance for Malignancy

• To Differentiate Self From Non-self To Differentiate Self From Non-self (Autoimmune diseases)(Autoimmune diseases)


ImmunityImmunityInnateInnate

The body’s 1st line of defense against infection.

It consists of barriers that are nonspecific and have no memory. (i.e. Repeat exposures to the same microorganism does not enhance their response.)

Adaptive / AcquiredAdaptive / Acquired

A SPECIFIC immune response which has MEMORY: upon second contact with an infectious agent the immune response will be faster and more potent than the first encounter with the same agent.


The Innate Immune System

Some references divided the innate immune system to:

Physical defences – skin, membranes, nose hairs, mucous.

Chemical defences – sweat, tears, saliva, stomach acid.

Biological defences – commensal bacteria, phagocytes, macrophages.


Continuation…• immediately available without having to adapt to

specific pathogens that are present.

• It is not specific to a particular organism such that identical responses can protect against several organisms.

• Germ line encode (evolved on an evolutionary time scale).

• mediated by phagocytes (cell that ingest bacteria or other particulate matter) such as macrophages and neutrophils.

• also mediated by chemical compounds that will be described later.


Continuation… Innate immunity relies on receptors that recognize

common bacterial (and other) molecules. The information on the structure of these receptors is germ line encoded. Thus, the number of different receptors is limited (<20 known) and these receptors cannot evolve as fast as most pathogens.

Pathogens sometimes modify or mask molecule recognized by the germ line encoded receptors. Virus are generally not recognized by these receptors.


Continuation…

Dendritic cells can pick-up stuff randomly (e.g., viruses) and present it to T cells (via a process that “unmasks” hidden antigens: antigen processing)

Lymphocytes have overcome the problem of a limited number of germline encoded receptors. Lymphocytes can somatically create 109 to 1016 different antigen receptors.


Components of Innate Immunity

Anatomic Anatomic barriersbarriers

Physiological Physiological barriersbarriers BiologicalBiological

( phagocytes/Endocytic) ( phagocytes/Endocytic) barriersbarriers

InflammationInflammationbarriersbarriers


Innate Defense MechanismsInnate Defense MechanismsMechanismMechanism FunctionFunction

A. Anatomic or Physical Barriers 1. “Flushing” mechanisms

a. Salivary flow Prevents bacterial overgrowth

b. Coughing & Sneezing Clears respiratory tract

c. Urination Flushes the urinary tract

d. Lacrimation Cleanses eyes

e. Ciliary action Expels mucous

2. Skin and Mucous Membranes Form a ‘wall’ between deep

tissues and pathogens.


Intact Skin is an Effective Barrier Against Most Pathogens

Mechanical Defenses

Mucous Membranes: Line gastrointestinal, genitourinary, and respiratory tracts.

Two layers: Outer epithelial and inner connective layer. Epithelial layer secretes mucus which maintains moist surfaces. Although they inhibit microbial entry, they offer less protection than skin. Several microorganisms are capable of penetrating mucous membranes:

Papillomavirus Treponema pallidum Enteroinvasive E. coli Entamoeba histolytica


Chemical or physiological Barriers

MechanismMechanism pH of body fluids

Lysozyme

Interferon

FunctionInhibits growth of many

pathogens

Breaks down cell walls of bacteria

Inhibits viral replication


Biological Barriers

MechanismMechanism Natural resistanceNatural resistance

Normal flora

Inflammation

Complement

Phagocytosis

Function Species resistance to

microbes Competes with

invaders Localizes and

destroys pathogens Cell lysis and

phagocytosis Engulfment of

pathogens


Physical Components of Defense:

SkinSkin

Epidermis

- Multiple layers of tightly packed cells - Shedding of dead skin cells removes attached

microorganisms - Epidermal dendritic cells

- Also termed Langerhans cells

- Phagocytize pathogens Dermis

- Contains protein fibers called collagen- Gives skin strength and pliability to resist

abrasions that could introduce microorganisms

By Dr Nasser AL-DAGHRI 21Figure 15.1


Line all body cavities open to the outside environment

Defend vs. microbes by mucus, cilia

Flushing mechanisms: coughs, sneezes

Physical Components of Defense; Mucous MembranesMucous Membranes


Physiological BarriersPhysiological Barriers

PH

Temperature

Chemicals Mediators


Sebum: Oily substance produced by sebaceous glands that forms a protective layer over skin. Contains unsaturated fatty acids which inhibit growth of certain pathogenic bacteria and fungi.

pH: Low, skin pH usually between 3 and 5. Caused by lactic acid and fatty acids.

Perspiration: Produced by sweat glands. Contains lysozyme and acids.

Lysozyme: Enzyme that breaks down gram-positive cell walls. Found in nasal secretions, saliva, and tears.

Chemical Defenses


Interferons (Cytokines)

Act as short-acting messengers that protect other cells in the vicinity from viral infection.

a interferon: Inhibits viral replication, increases NK cells, and

induces MHC-I antigens. b interferon:

Inhibits viral replication, increases NK cells, and induces MHC-I antigens.

g interferon: Activates macrophages and induces MHC-II

antigens. Immunological defense against infection and

cancer.


Interferons (IFNs)

Figure 16.16

1

2

3

4

5

Viral RNA from an infecting virus enters the cell.

The infecting virus replicates into new viruses.

The infecting virus also induces the host cell to produce interferon on RNA (IFN-mRNA), which is translated into alpha and beta interferons.

Interferons released by the virus-infected host cell bind to plasma membrane or nuclear membrane receptors on uninfected neighboring host cells, inducing them to synthesize antiviral proteins (AVPs). These include oligoadenylate synthetase, and protein kinase.

New viruses released by the virus-infected host cell infect neighboring host cells.

6 AVPs degrade viral m-RNA and inhibit protein synthesis and thus interfere with viral replication.


Interferons


Biological barriersBiological barriers ( phagocytes/Endocytic) ( phagocytes/Endocytic)

1. Complements

2. Phagocytosis

3. Inflammations


Biological Barriers

1. ComplementComplement – a group of heat-labile proteins, produced by the liver, consisting of 9 major components from C1 to C9. When activated these proteins contribute to destruction of bacteria. Complement is activated by several pathways:

Classical PathwayClassical Pathway – – C1 is activated when it binds to antigen-antibody complexes. Sequential activation of the complement ‘cascade’ follows.

Alternate PathwayAlternate Pathway – – C3 is activated by directly by pathogen surfaces (i.e. bacterial cell wall components such as polysaccharide) or by damaged tissue at sites of inflammation.


The complement proteins are designated C-1 to C-9. These proteins are in an inactive state.

Become activated by the attachment of antibodies to antigens.

Complement proteins can be subdivided into 3 components: C1: recognization. C4, C2, C3: activation. C5-C9: attack (complement fixation).

The Complement System


Continuation… Classic pathway: Antibodies of IgG and IgM attach to antigens on invading

cell membranes. Binding to C1 activates the process.

Activated C1 hydrolyzes C4 into C4a and C4b.

C4b binds to the cell membrane and becomes an active enzyme.

C4b splits C2 into C2a and C2b.

C2a attaches to C4b and cleaves C3 into C3a and C3b. Alternate pathway converges with classic pathway.

Fragment C3b becomes attached to the complex in the cell membrane.

C3b converts C5 to C5a and C5b.


Fixation of Complement Proteins


Complement Fixation

C5b and C6 through C9 are inserted into bacterial cell membrane, to form a membrane attach complex (MAC). Create large pores in membrane, causing osmotic influx of H20.

Complement proteins kill the cell.


Complement Fragments

Chemotaxis: C5a acts as a cytokine to attract neutrophils

and monocytes to the site. Attract phagocytes.

Opsinization: Phagocytes have receptors for C3b.

Form bridges between phagocyte and victim cell.

C3a and C5a stimulate mast cells to secrete histamine: Increase blood flow and capillary permeability.

Bring in more phagocytes.

By Dr Nasser AL-DAGHRI 35Figure 15.13


Alternate PathwaysAlternate Pathways


Classical Pathway

Figure 16.13


Alternative Pathway

Figure 16.14


Lectin Pathway

Figure 16.15


1. Cytolysis: Due to the formation of a membrane attack complex (MAC) which produces lesions in microbial membranes.

2. Inflammation: Complement components (C3a) trigger the release of histamine, which increases vascular permeability.

3. Opsonization: Complement components (C3b) bind to microbial surface and promote phagocytosis.

4. Inactivation of Complement: Regulatory proteins limit damage to host cells that may be caused by complement.

Consequences of Complement Activation


Innate Immunity – Biological Innate Immunity – Biological BarriersBarriers

Phagocytosis – a process by which cells Phagocytosis – a process by which cells engulf material and enclose it within an engulf material and enclose it within an intracellular compartment (phagosome)intracellular compartment (phagosome)

GranulocytesGranulocytes(espec(especially neutrophilsially neutrophils))

Monocytes/Macrophages (Wandering

macrophages, fixed macrophage or histiocyte)

Acute phagocytic Acute phagocytic response to infectionresponse to infection

Phagocytic against microbes and Phagocytic against microbes and worn-out blood cells as infection worn-out blood cells as infection progresses; also involved in cell-progresses; also involved in cell-

mediated immunitymediated immunity


____________ and ___________ are main phagocytes Phagocytosis takes place in 5 stages

Phagocytosis


Attachment

Phagocytosis of Bacteria

Ingestion

Fusion of phagosomeand lysosome

Digestion

Release of digestion products from the cell


Innate Immunity: Phagocytosis & Inflammation

Figure 24-6: Phagocytosis


Biological BarriersBiological Barriers Inflammation – an immunological response to – an immunological response to

tissue injury involving vascular changes and tissue injury involving vascular changes and recruitment of neutrophils and macrophages by recruitment of neutrophils and macrophages by cytokinescytokines. .

CytokinesCytokines - biologically active proteins that target - biologically active proteins that target other cells. During inflammation, they:other cells. During inflammation, they:1) Affect the local microcirculation by causing 1) Affect the local microcirculation by causing vasodilation and increased vascular permeability. vasodilation and increased vascular permeability. 2) Recruit neutrophils, in turn, release substances 2) Recruit neutrophils, in turn, release substances which may contribute to further tissue damage which may contribute to further tissue damage and vasodilationand vasodilation. .


1. 1. Calor Calor (Heat)(Heat)

2. Dolor 2. Dolor (Pain)(Pain)

3. Rubor 3. Rubor (Redness)(Redness)

4. Tumor 4. Tumor (Swelling)(Swelling)

Classic features of inflammation:


Enhances the effects of interferons

Inhibits growth of some microorganisms

May enhance the performance of phagocytes, cells of specific immunity, and the process of tissue repair

Benefits of Fever

1. Destroy and remove pathogens

2. If destruction is not possible, to limit effects by confining the pathogen and its products.

3. Repair and replace tissue damaged by pathogen and its products.

Functions of Inflammation


1. Vasodilation: Increase in diameter of blood vessels. Triggered by chemicals released by damaged cells: histamine, kinins, prostaglandins, and leukotrienes.

2. Phagocyte Migration and Margination: Margination is the process in which phagocytes stick to lining of blood vessels.Diapedesis (Emigration): Phagocytes squeeze between endothelial cells of blood vessels and enter surrounding tissue.

Stages of Inflammation


Phagocytes are attracted to site of infection through chemotaxis.

Phagocytes destroy microbes, as well as dead and damaged host cells.

3. Tissue Repair: Dead and damaged cells are replaced.

Continuation…


Process of Inflammation


The Cardinal Signs of Inflammation

Redness

Swelling

Heat

Pain Caused by cytokines and other chemical mediators

Caused by vasodilatation and movement of cells and/or fluid into the interstitial spaces

Ultimately controlled by endothelial cells


The Immune System

http://apc.ucc.ie


Adaptive Immune System(2) The adaptive immune system has two notable

properties: Specificity – it responds to a specific

antigen by producing a specific antibody or cytotoxic cell.

Memory – it retains a memory of previous antigens, and can respond more rapidly when invaded again.

This is why we rarely get certain disease more than once – i.e. we develop immunity.

This is the principle behind immunisation – vaccines trigger the adaptive immune system without causing illness.


Adaptive Immune System(1)

Triggered by antigens – e.g ‘foreign’ proteins found on bacteria, viruses, pollen, etc…

Two types of response: Hummoral (or serum) – B-lymphocytes create

proteins called antibodies (or immunoglobulin) which lock onto the antigens.

Cellular – ‘helper’ T-lymphocytes activate ‘killer’ T-lymphocytes.


Adaptive Immunity Specific Immune Response (e.g., antibody) against a

particular microorganism is an adaptive immune response. That is, it occurs during one’s lifetime as an adaptation to the presence of that particular organism.

An adaptive immune response might provide lifelong protective immunity to a given pathogen.

These are central principles of adaptive immunity Specific immunity can be induced by a variety of

substances. Things that induce adaptive immunity are called ANTIGENS

Antigen-specific responses are mediated by lymphocytes


Principles of Adaptive Immune Responses

Specific recognition of individual antigens by immune cells via antigen receptors

Clonal selection and expansion occurring after antigenic recognition- PRIMARY IMMUNITY Generation of effector T cells and B cells

Later exposure to the same antigen: SECONDARY (MEMORY) RESPONSE Rapid proliferation of memory cells


Antigen recognitions and effector mechanisms of adaptive immunity

Generally

Antibody

T cells

T cells (antibody)

Antibody


Adaptive Defense MechanismsAdaptive Defense Mechanisms

MechanismMechanism FunctionFunction

A.A. Humoral Immunity AntibodiesHumoral Immunity Antibodies bind foreign antigens bind foreign antigens andand

(B lymphocytes) contribute to immunity by: neutralization, (B lymphocytes) contribute to immunity by: neutralization, increasing phagocytosis (opsonization) and increasing phagocytosis (opsonization) and

Complement Complement activation.activation.

B.B. Cellular ImmunityCellular Immunity Responsible for immunity against Responsible for immunity against (T lymphocytes) (T lymphocytes) intracellular pathogens (viruses) andintracellular pathogens (viruses) and

surveillance for malignancy. surveillance for malignancy.


Cellular componentsCellular components


Cell Type # Cells/mm3FunctionErythrocytes (RBC) 4.8-5.4 million Transport O2 and

CO2

Leukocytes (WBC) 5000-9000 Various A. Granulocytes: 1. Neutrophils (70% of WBC) Phagocytosis 2. Basophils (1%) Produce histamine 3. Eosinophils (4%) Toxins against parasites

some phagocytosis

B. Monocytes/Macrophages (5%) Phagocytosis

C. Lymphocytes (20%) Antibody

production (B cells) Cell mediated

immunity (T cells)

Platelets 300,000 Blood clotting

Cellular Elements of Blood


B lymphocytes – mature in Bone marrow lymphatic tissue, especially spleen and lymph nodes T lymphocytes – mature in the Thymus

Lymphocytes

Large nucleus


B lymphocytes make antibodies = immunoglobulins

1000s of different B cells, each recognises a different antigen on the surface of a macrophage. Each antigen stimulates production of a single specific antibody

B cells (along with T cells) come in contact with antigen. They are stimulated (by T cells) to produce many clones, plasma cells, which make antibodies.

B-lymphocytes

Antibodies•Can bind to pathogens and prevent them from infecting cells. Pathogens are then destroyed by phagocytes•Can inactivate pathogens by causing them to clump together•Can trigger the complement system, resulting in pathogens being burst

Memory B cells – faster, more sensitive reaction = secondary response


B-Cells

B-Cells are the generators of Humoral Immunity, so called because it consists of soluble proteins found in the "Humors," (Blood). Every B-Cell has an ImmunoGlobulin (Ig) molecule on its surface, due to Genetics.

Each of those ImmunoGlobulins recognizes a unique three-dimensional Epitope. In the Bone Marrow, millions of different B-Cells are created daily, and then proceed to circulate throughout the bloodstream.


Since each has a different ImmunoGlobulin, each will bind to a different substrate. It is most often the case that a B-Cell will find nothing to bind to in its short lifespan, and rapidly be replaced by a new B-Cell.

In the event that a B-Cell's ImmunoGlobulin does find a substrate, that B-Cell will Clonally Expand, resulting in many B-Cells which recognize the same target.

Over time, the clones' ImmunoGlobulin Genes will mutate to improve the affinity for the target even more.

Continuation…


B-Cells also differentiate into Plasma Cells and Memory Cells

Plasma Cells will proceed to secrete vast quantities of ImmunoGlobulins, which will be identical to their parent's original surface.

These ImmunoGlobulins (or Ig's) will pass throughout the blood and attach to the foreign object, either disabling it themselves or summoning a Non-Specific Effector Cell.


Memory Cells by contrast are much smaller than Plasma Cells and don't immediately secrete anything. Instead, they persist in the body for many years and may never be activated.

However, in the event that the same foreign Organism returns, they will develop into Plasma Cells much more rapidly than the original B-Cells and proceed to secrete their ImmunoGlobulins.

Continuation…


MacrophagePhagocytoses pathogen and displays antigens on surface

B-cellsEach recognise a different antigen. The correct one develops into…

Plasma cellsClones of the correct B-cell, which produce antibodies

1st meeting a pathogen, this process takes 10-14 daysMemory B cell= subesquent meetings, takes about 5 days

How B-cells work…

Pathogen (e.g. bacteria, virus)

Macrophage


T-lymphocytes

Helper T-Cells•Recognise antigens on surface of leukocytes, especially macrophages•Enlagre and form a clone of T-helper cells•Secrete interferon and cytokines which stimulate B-cells and stimulate killer -cells•Can be infected by HIV

Killer T-CellsAlso called cytotoxic•Destroy abnormal body cells, e.g. virus infected or cancer cells•Stimulated by cytokines (THcells)•Release perforin, which forms pores in target cells. This allows water and ions in = lysis

Suppressor T-Cells•Control the immune system when the antigen /pathogen has been destroyed•Only recently discovered so little is known about them

Memory T-Cells•Can survive a long time and give lifelong immunity from infection•Can stimulate memory B-cells to produce antibodies•Can trigger production of killer T cells

Mature in Thymus, which is most active just before and after birth. The thymus starts to shrink during puberty.


Each T-Cell has a unique surface molecule much like an ImmunoGlobulin's, called a T-Cell Receptor (TCR).

Unlike Ig's that can recognize any molecule, the TCR is restricted to recognize only short Amino Acid Chains, displayed on the surface of cells, in conjunction with a molecule, called the (Major Histocompatibility Complex (MHC

Continuation…


Abnormal cell e.g cancer cell, infected cell

Normal cell

Antigen

Killer T-cell recognizes antigen

Clones of killer T-cell attach to antigen

Helper T-cell stimulates correct killer T-cell to multiply

Killer T-cells release perforin pores

Abnormal cell gains water, swells and bursts

Helper T-cell also stimulates B-cells to make antibodies

Memory T-cells stay in circulation

Suppressor T-cells turn off immune response

XX

X

How T-cells work…


Myeloid Cells Granulocytes

General Charactistics comprise 41-81% of blood leukocytes 20-30 µm in diameter have a multi-lobed nucleus:

with loosely packed strands of intensely basophilic chromatin

surrounded by a moderate amount of lightly basophilic cytoplasm containing large numbers of granules


Neutrophils - comprise 40-75% of blood leukocytes - contain small, lightly staining granules - phagocytic effectors of antibody-mediated immunity and hypersensitivity

Eosinophils - comprise 1-5%of blood leukocytes - contain orange-to-red staining granules - help regulate inflammatory responses - active in antibody-mediated cytolysis of immature forms of intestinal parasites

Basophils - comprise 0-1%of blood leukocytes - contain large, blue-black staining histamine-rich cytoplasmic granules and FcR

that bind IgE molecules - help generate inflammatory responses - mediators of immediate (type I) hypersensitivity

Mast Cells - tissue cells with histamine-rich cytoplasmic granules and FcR that bind IgE

molecules (~10X more of each than found in basophils) - help generate inflammatory responses

Types of Granulocytes


comprise 3-7% of blood leukocytes 20-50 µm in diameter nucleus is large and indented:

contains loosely packed strands of intensely basophilic chromatin

surrounded by a large amount of lightly basophilic cytoplasm

cytoplasm contains numerous granules and occasional vacuoles

engulf and digest foreign matter phagocytic effectors of cell-mediated immunity and

hypersensitivity

Monocytes


derived from monocytes after they migrate into tissues (e.g. histiocytes in connecitve tissue, alveolar macrophages in lung, microglial cells in CNS, mesangial cells in kidney, Kupffer cells in liver, osteoclasts in bone, etc.)

nucleus is large and indented: contains loosely packed strands of intensely basophilic

chromatin surrounded by a large amount of lightly basophilic cytoplasm

cytoplasm contains numerous granules and vacuoles, especially when activated by T lymphocyte cytokines, such as interferon-gamma

engulf and digest foreign matter active in antigen processing and presentation phagocytic effectors of cell-mediated immunity and

hypersensitivity

Macrophages


Dendritic Cells are covered with long membrane extensions (that make them look like dendrites in nervous tissues ... hence the name)

Circulating dendritic cells constitute 0.1% of blood leukocytes and are also found in

lymph ("veiled" cells) develop into mature tissue dendritic cells (?)

Interdigitating dendritic cells found in T cell rich regions of secondary lymphoid tissues process and present antigen to T cells

Interstitial dendritic cells found in most organs ... lungs, liver, heart, kidney, digestive

tract, etc. process and present antigen to T cells

Langerhans cells found in epidermis of skin process and present antigen to T cells

Continuation…


Key Cells & Overview of their Function in Immune Defense

Figure 24-4: Cells of the immune system


A process that facilitates A process that facilitates

phagocytosis by coating antigens phagocytosis by coating antigens

with opsonin (e.g. antibody and with opsonin (e.g. antibody and

C3b).C3b).

OPSONIZATIONOPSONIZATION


IgG and C3b are known as opsonins and the

process of attachment is called opsonization

IgG and C3b are known as opsonins and the

process of attachment is called opsonization

www.cat.cc.md.us/.../ opsonization/u1fig26n.html Phagocytic cell

Receptor for IgG

Receptor for iC3b(high & low avidity)

*subclasses differ in C’ deposition capacity


Antibody Roles in Host DefenseAntibody Roles in Host Defense

22 . .Opsonization Opsonization - - antibodies or complement antibodies or complement (C3b) coat an antigen signaling it as foreign (C3b) coat an antigen signaling it as foreign to phagocytes who then ingest and destroy to phagocytes who then ingest and destroy itit..


Mechanism of Opsonization

mature dendritic cells are (professional) antigen presenting cells (APC)


Adaptive immune response begins with the uptake of antigens by immature dendritic cells

Macropinocytosis by dendritic cells(receptor-mediated and random)

Figure 1.13

Dendritic cells take up antigen to present to T cell. They do not constitute an effective mechanism against pathogens as do macrophages and neutrophils.*High endothelial venule (HEV)(i.e., specialized post capillary blood vessel)

*


Acquired Immunity: Antigen-Specific Responses

Figure 24-13: Functions of antibodies


AntigenAntigen – any substance that induces an – any substance that induces an adaptive immune response. It can be protein, adaptive immune response. It can be protein, complex polysaccharide, lipids and even complex polysaccharide, lipids and even nucleic acid when associated with proteinnucleic acid when associated with protein..

Epitope Epitope – the specific region(s) of an antigen – the specific region(s) of an antigen that stimulates the immune responsethat stimulates the immune response

DefinitionsDefinitions


Epitopes: Antigen Regions that Interact with Antibodies


Basic Reaction in Basic Reaction in ImmunologyImmunology

Ag + Ab AgAb

AgAb Complex

EpitopeParatope

Ag = Antigen Ab = Antibody

Ag

Ab ~106 - 108

different Ab specificities!


Specific Defence System (Adaptive Immune System)

Antigens – foreign molecules that generate antibody production

Antibodies (immunoglogulins) – proteins produced by lymphocytes in response to antigens

Monocytes – develop into macrophages which phagocytose foreign particles (antigens) Lymphocytes -


Proteins that recognize and bind to a particular antigen with very high specificity.

Made in response to exposure to the antigen. One virus or microbe may have several antigenic

determinant sites, to which different antibodies may bind.

Each antibody has at least two identical sites that bind antigen: Antigen binding sites.

Valence of an antibody: Number of antigen binding sites. Most are bivalent.

Belong to a group of serum proteins called immunoglobulins (Igs).

Antibodies


Antibody Structure


Classes of ImmunoglobulinClasses of Immunoglobulin

There are five major classes of antibodies which have diverse functions.

1. IgM (Immunoglobulin M) The class of serum antibody first produced during an

infection. It is a large pentameric molecule that is active in agglutination pathogens and activating complement.

2. IgG (Immunoglobulin G) The predominant immunoglobulin class in serum. Has

function such as neutralizing toxins, opsonizing bacteria, activating complement and crossing the placenta to protect the fetus and neonate.


1. IgA (Immunoglobulin A)

The class of immunoglobulin that is present in dimeric form in many body secretions (e.g., saliva, tears, bronchial and intestinal secretions) and protects body surfaces.

4. IgE (Immunoglobulin E) The class of immunoglobulin that binds to mast

cell and basophils, and is responsible for type I or anaphylactic hypersensitivity. It is also involved in resistance to helminth parasites.

5. IgD (Immunoglobulin D) The class of immunoglobulin found on the

surface of many B lymphocytes; thought to serve as antigen receptor in the stimulation of antibodies synthesis.

Continuation…


Immunoglobulin function by class

IgM: The BCR of naive cells. The antibody is a pentamer. IgM antibodies appear first in the primary immune

response. Neutralization (toxins, bacteria, viruses); complement

activation. IgG:

the BCR of most memory cells. Has four types (IgG1, IgG2, IgG3, IgG4; a monomer. Most prevalent in serum. The only antibody small enough to cross the

placenta into the fetal blood and protect the newborn from infection.

Neutralization, Opsonization, complement activation.


Continuation…

IgA: Crosses over into the intestines. Protects mucosal layers from pathogens by

neutralization. Has two types; monomer or dimer.

IgE: Activation of Basophils and Mast cells. Involved in allergies.

IgD: Appears on transitional naive B cells. Role: unknown.


Structure: Dimer Percentage serum antibodies: 10-15% Location: Secretions (tears, saliva, intestine,

milk), blood and lymph. Half-life in serum: 6 days Complement Fixation: No Placental Transfer: No Known Functions: Localized protection of

mucosal surfaces. Provides immunity to infant digestive tract.

Immunoglobulin ClassesIII. IgA


Structure: Monomer Percentage serum antibodies: 0.2% Location: B-cell surface, blood, and lymph Half-life in serum: 3 days Complement Fixation: No Placental Transfer: No Known Functions: In serum function is

unknown. On B cell surface, initiate immune response.

IgD


Immunoglobulin ClassesV. IgE

Structure: Monomer Percentage serum antibodies: 0.002% Location: Bound to mast cells and basophils

throughout body. Blood. Half-life in serum: 2 days Complement Fixation: No Placental Transfer: No Known Functions: Allergic reactions. Possibly

lysis of worms.


In a single Ig molecule, the C-termini amino acid sequences of the light chains (110 of ~220 total aa) are identical to each other. They are similar or identical to the light chain C-termini in all Igs, regardless of their specificity. Thus, this part of the molecule is called the light chain constant region.

There are two major Ig light chain constant region types (similar but different aa sequences). These DO NOT determine the class/isotype of the Ig and DO NOT link the molecule to effector functions

•The 2 major Ig light chain types are k (kappa) and l (lamda)

The Constant regions of Igs: (part 1, the light chains)

Constant region of the heavy chain = CH

Constant region of the light chain = CL


In a single Ig molecule, the C-termini amino acid sequences of the 2 heavy chains (330 of ~440 total aa) are identical to each other. They are similar or identical to the heavy chain C-termini in all Igs, regardless of their specificity. Thus, this part of the molecule is called the heavy chain constant region.

The Constant regions of Igs: (part 2, the heavy chains)

Constant region of the heavy chain = CH

Constant region of the light chain = CL


The five Ig classes are:IgM, IgG (Human: IgG1, IgG2, IgG3, IgG4) (mouse: IgG1,

IgG2a, IgG2b, IgG3), IgA (Human IgA1, IgA2), IgD and IgE

There are also sub classes (4 IgG subclasses and 2 IgA subclasses in humans.

Isotype means the same thing as class and subclass; thus, in humans, there are 9 isotype: IgG1, IgG2, IgG3, IgG4, IgA1, IgA2, IgM, IgE and IgD. For mice, IgG1, IgG2a, IgG2b IgG3, IgA, IgM, IgE and IgD.


Greek letters are used to name the Greek letters are used to name the heavy and light chain constant regionsheavy and light chain constant regions

g, m, a, d, e for the heavy chainsk, l for the light chains (k:l = 2:1 human; 20:1mice;

1:20 bovine)

Q: What is the isotype of this Ig?

A: IgA

Q: what is the name of heavy and light chains that are not labeled?

?

?

A: and

For example;

The heavy chain determines the class of the Ig, thus

If the heavy chain is the class is IgG (and 1 for IgG1, etc.)

If the heavy chain is the class is IgM

If the heavy chain is the class is IgA

If the heavy chain is the class is IgD

If the heavy chain is the class is IgE

IgG

Different heavy chains provide different functions; there is no known difference in function for and

IgG IgD


B cells develop from stem cells in the bone marrow of adults (liver of fetuses).

After maturation B cells migrate to lymphoid organs (lymph node or spleen).

Clonal Selection: When a B cell encounters an antigen it recognizes, it is stimulated and divides into many clones called plasma cells, which actively secrete antibodies.

Each B cell produces antibodies that will recognize only one antigenic determinant.

How Do B Cells Produce Antibodies?


A. Primary antibody response. It is stimulated during immunization

procedures (and also in naturally acquired immunity) the type of immunoglobulin is (IgM) and it is characterized by low antibodies titer.

B. Secondary antibody response. It is characterized by producing the (IgG)

type of immunoglobulin with high level and affinity for the antigen. It depends on the formation of the memory B cells.

Types of antibody responseTypes of antibody response


AntibodyTiter

Days

7 14 21 28 35 42

IgG

IgM

Primary antibody response

Secondary antibody response

Diagram show the primary and secondary antibody response and the types of immunoglobulin


Continuation…


Primary immunization (primary response) is relatively:

Secondary immunization (secondary response or booster immunization) is relatively:

slow (4-7days)small (low concentration of antibody)low affinity antibodyIgM first, IgG second (equal amounts of IgM and IgG)

fast (2-4 day)large amounts of antibodyhigh affinity antibodymostly IgG


Often, a secondary response is so fast and effective in removing antigens (pathogens), there are few or no symptoms detected by the infected individual (protective immunity).

Secondary responses are the reason we do not get certain infectious diseases more than once.

Secondary responses also explain why vaccinations work. For vaccinations, instead of immunizing with something that makes you sick, a vaccine contains antigens that are expressed on the pathogen but the vaccine is usually not pathogenic (e.g., live organism that is not pathogenic, dead organism, purified protein, others).

Continuation…


Induced Immunity

Active immunityProduction of a person’s own

antibodies. Long lasting

Passive immunityAn individual is given antibodies by

another Short-term resistance (weeks- 6months)

Natural ActiveWhen pathogen

enters body in the normal way, we make antibodies

Natural PassiveBaby in utero

(placenta)Breast-fed babies

Artificial PassiveGamma globulin

injectionExtremely fast, but

short lived (e.g. snake venom)

Edward Jenner

Artificial ActiveVaccination –

usually contains a safe antigen from

the pathogen. Person makes

antibodies without becoming ill


Flow of lymph


Where does it all happen? (1)

Primary lymphoid organs:Antigen-independent differentiation Bone marrow :

Initial differentiation of all lymphocytes;

B lymphocyte development and selection.

Thymus : T lymphocyte development and selection.


Where does it all happen? (2)

Blood: lymphocyte circulation. Tissue: fight against infections. Lymph: return to circulation. Spleen: blood filtration.

Secondary (peripheral) lymphoid organs: Lymph Nodes, Spleen, and diffuse

immune tissues: interaction with APCs and other lymphocytes; decisions; learning and memory.


Immune System Organs: Lymph Nodes


MHC class IMHC class I peptide-binding motifs are characterized as having:

8-10 amino acids

anchors at termini

anchors in the middle Since there are hundreds of different MHC class I proteins in a species (polymorphic and polygenic)(only a few in each individual) there are hundreds of MHC class I binding motif in a species

Major Histocompatibility Complex


Immune System Organs (Spleen)


CYTOKINES

Cytokines are a group of low molecular weight regulatory proteins secreted by leukocytes as well as a variety of other cells in the body in response to stimuli. Membrane-bound forms of some of the secreted cytokines are known as well.

Cytokines regulate the intensity and duration of the immune response by stimulating or inhibiting the activation, proliferation, and/or differentiation of various cells, and by regulating the secretion of antibodies or other cytokines or mediators.

Almost ALL cells secrete at least a few cytokines (why they arenot called lymphokines or monokines any more).


CYTOKINES BY FUNCTION

CYTOKINES THAT MEDIATE AND REGULATE INNATE IMMUNITYType I interferons— Dr. Pestka’s lectureTumor necrosis factor-aInterleukins 1, 6, 10, 12, 15, 18, and moreChemokines—a special subclass; won’t deal with here

CYTOKINES THAT MEDIATE AND REGULATE SPECIFIC IMMUNITYInterleukins 2, 4, 5, 13, 16, 17, and moreInterferon-g (Type II interferon; Dr. Pestka’s lecture)Lymphotoxin-a (Tumor necrosis factor-b)

CYTOKINES THAT STIMULATE HEMATOPOIESISc-kit ligandInterleukins 3, 7, 9, 11, moreColony stimulating factors— M-CSF, G-CSF, GM-CSF, EPO, TPO

Overlapping functions are common.


Each immunoglobulin chain comprises domainsDomains are discrete, compactly folded regions of a protein.

Each light chain comprises 2 domains and each heavy chain comprises 4 or 5 domains

In immunoglobulin, the domains are structurally similar but not identical (similar amino acid sequences and folding) and thus referred to as immunoglobulin domains. Many other proteins fold similarly and are said to belong to the immunoglobulin super family.

Domains, by themselves or via interactions with other domain, form functional units.

In immunoglobulin, the domains are structurally similar but not identical (similar amino acid sequences and folding) and thus referred to as immunoglobulin domains. Many other proteins fold similarly and are said to belong to the immunoglobulin super family.

Domains, by themselves or via interactions with other domain, form functional units.

When comparing many antibodies, amino terminal domains are highly variable. Within an isotype, the remaining domains are constant (i.e., all IgM CH1are essentially identical, all CH2 are essentially identical; CH1 and CH2 are similar but not identical)


Five major classes of antibodies

IgG IgM IgA IgD IgE

IgM

heavy chain heavy chain

IgG

Also and heavy chains

Each class has different functions and/or distributionLots of specificities needed but only a few functions are necessary

Immune response always start with IgM: once a response begins, the class of the response can change and the response can simultaneously comprise several classes (class switching)

The class of the antibody is determined by the constant region of the heavy chain (thus, function is determined by the heavy chain only)


Heavy and light chains are disulfide linked (interchain disulfide bond)

Heavy chains are disulfide linked (interchain disulfide bond)

Each immunoglobulin domain has an intrachain disulfide bond

Continuation…


Different ways to depict an Ig molecule


Prime (‘) because F(ab’)2 is more than just 2 Fab

The ag binding specificity of the Fab and F(ab’)2 is exactly like that of the whole molecule. However, other properties of the Ig molecule are lost. For example…

Fragment antigen binding = Fab

Fragment crystallizable = Fc


Flexibility in the hinge region allows binding to surfaces or antigens with various shapes or orientations.

Anti-red antibodyAnti-red antibody anti-green anti-green antibodyantibody

Although not shown, antigens with three (or more) sites where three (or more) antibodies can bind simultaneously, allow for three-dimensional antigen-antibody complex of enormous size.

Multiple binding sites allows for stronger binding (higher avidity) and for cross-linking antigens into complex matrices


Ig domains have similar structures

(i.e., immunoglobulin folds)

Many other molecules have a similar structure (Ig-like domains) and constitute the immunoglobulin (Ig) superfamily.

Although the variable domains of the H and L chains are highly variable (determining the specificity of the antibody) they are still recognizable as Ig domains

Here, the light chain constant region (CL) has the Ig fold.


The antigen binding site is made-up of both heavy and light chain CDRs

Fig. 3.8

Antigen(peptide)

CDRs shown in colors other than light blue


TCR plus CD4 interacting with MHC class II plus peptide

membrane

membrane


Expression of MHC class I and class II proteins


MHC class IMHC class I MHC class II


MHC Class I

MHC Class II

MHC Class II

MHC Class I


MHC class I +peptide

MHC class I


Functions of antibodies

Neutralization of toxins; of bacteria and viruses by interfering with their binding to cells, etc.

Opsonization: coating pathogens and increasing their phagocytosis.

Antibody-mediated cytotoxicity (activation of killer cells).

Activation of Mast cells and basophils, which release granules of inflammatory molecules.

Activation of Complement a series of molecules that binds to the antibody constant part, and eventually makes holes in the (bacterial) cell wall.


Proliferation and differentiation of the T cell to effector function

(Mature naive T cell) (Armed effector T cell)

For example

The two signal model for lymphocyte activation

(antigen alone is insufficient)

(Mature dendritic cell)

Proliferation and differentiation of the B cell to effector function

For example

Pla

sma

c ell


Professional antigen presenting cells


Antigen recognitions and effector mechanisms of adaptive immunity

General

Antibody

T cells

T cells (antibody)

Antibody


Different Ig isotypes (classes) provide for different functions.

Also, different isotypes have different distributions [blood, secretions (mucus, saliva, tears, milk), cross the placenta].

Humoral immunitythe immunity mediated by antibodies


TH2 cells control (activate) B cells.

Cell-mediated Immunity (CMI)

Other T cells (TH1 and CTL) deal with intracellular (inside a cell) pathogens. Intracellular pathogens (some bacteria and all viruses) are found in vesicles or in the cytoplasm. Vesicular and cytoplasmic pathogens are usually dealt with differently.

Continuation…


CTLs have CD8 on their surface and are sometimes referred to as CD8+ T cells.

Continuation…


TH1 and TH2 T cells have CD4 on their surface and are sometimes referred to as CD4+ T cells.

TH1 T cells are sometimes referred to as inflammatory T cells

cytokines

Continuation…


The two signal models for lymphocyte activation

(antigen alone is insufficient)

Proliferation and differentiation of the T cell to effector function

(Mature naive T cell) (Armed effector T cell)

For example

(Mature dendritic cell)

Proliferation and differentiation of the B cell to effector function

Clonal selection for TH cell

TH2

TH2 cells are sometimes referred to as helper T cells

Clonal selection for B cell


CTL deal with antigens in the cytoplasm

TH1 deals mostly with antigen in macrophage vesicles (antigens that have been phagocytized)

TH2 deals with antigens that were bound to BCRs (extracellular antigens) and internalized (in vesicles) the by B cells

For antigens to be recognized by T cells, the antigen must get into a cell, be processed into peptides and presented in association with MHC proteins (see next slide)

Continuation…


(Insid

e cel

l)

(Out

side

cel

l)

T cells recognize foreign antigen as peptides bound to proteins encoded in the

major histocompatibility complex (MHC)

MHC is polymorphic (lots of allelic variants)


T Helper (CD4+ ) Subsets

Th2 responseHumoral Immunity

Acute Hypersensitivity

IL-4IL-10IL-13IL-5IL-6

Anti-InflammatoryCytokines

Th2TRAIL

IL-4

Th0

IFN-IL-2LT

Pro-InflammatoryCytokines

Th1

FasL

DR4

Th1 responseCellular Immunity

DTH

Suicide

Fas

AntigenAPC

IL-12


MHC class I gets its peptides from the cytoplasm (i.e., proteins synthesized in the cell)

MHC class Ipeptide

peptide

Protein

ribosome

mRNA

Some cytoplasmic proteins are chopped into peptides and transported into the ER

peptdespeptdes


Continuation…MHC class II gets its peptides from the proteins transported into the cell from the outside (i.e., proteins synthesized outside of the cell)


For antigens to be recognized by CTLs, they must be presented in association with MHC class I.

For antigens to be recognized by TH1 or TH2, they must be presented in association with MHC class II.

Therefore, CTLs are interested in proteins synthesized inside a cell whereas TH1 and TH2 are interested in proteins that were synthesized outside of a cell but were brought into the cell in vesicles

Why is that important to the immune system?

Continuation…


CD8 is a transmembrane protein found on CTLs and is a co-receptor for MHC I


cytokines

TH2

Inflammatory T cell

CD4

CD4 is a transmembrane protein found on TH1 and TH2 cells and is a co-receptor for MHC II

CD4

Continuation…


A (VERY) SHORT HISTORY OF CYTOKINES

1957-- Isaacs & Lindemann describe IF- in virally-infected chick chorioallantoic membranes1965 -- Wheelock describes IF- in PHA-treated leukocytes

1966 -- MIF described by David & Bloom in sups of Ag-stimulated lymphocytes

Photomicrograph from original paper depicting Ag-specific MIF production by guinea pig peritoneal cells.

10 Rx: NONE OVA TOXOID

20 Rx: NONE

OVA

TOXOID

MIF is here


Cytokines differ from growth factors in the structure of the receptor.

PLASMAMEMBRANE

TRANSMEMBRANEDOMAIN

gp130

JAK DOCKINGSITES

JAK

IL-6R

Lacks Tyr kinase domainJAK (a kinase) docks instead

IGF-1R

Has Tyr kinase domain


Most of the cytokine-binding receptors that function in the immune and hematopoietic systems belong to this receptor family. There are conserved amino acid sequence motifs in the extracellular domain - 4 positionally conserved Cys residues (CCCC) and a conserved sequence of Trp-Ser-X-Trp-Ser (WSXWS) where X is a nonconserved amino acid. The receptors consist of 2 polypeptide chains: a cytokine-specific subunit and a signal-transducing subunit which is usually not specific for the cytokine. In a few cases these receptors are trimers. The signal transducing subunit is required for high affinity binding of the cytokine.

MOST CYTOKINE RECEPTORS ARE IN 2 CLASSES

CLASS I CYTOKINE RECEPTORS

CLASS II CYTOKINE RECEPTORS

These receptors possess the conserved cysteine motifs, but lack the WSXWS motif present in class I cytokine receptors. The IFs bind to Class II receptors.


Interleukin-1 Stimulates TH cells

Interleukin-2 Activates TH,B, TC, &NK cells

Interleukin-12 Differentiation of CD4 cells -Interferon Increase activity of

macrophages Chemokines Cause leukocytes to move

to infection

Immune system cells communicate via cytokines


Interleukins are polypepetide molecules that have an important role in the immune system.

These polypepetides are secreted by lymphocytes, spherical cells that mediates specificity of immune responses.

Concentrating on interleukin 1, interleukin 2, and interleukin 3, each originate from different processes.

Although as cytokines all are similar in function; they have different factors that affect their synthesis and production.

Continuation…


Regulation and control of these three interleukins vary by the different producers, activators, and inhibitors or by which they are synthesized.

Interleukin 1 and 2 are similar in the way they are synthesized. Interleukin 3 has a simpler process of being produced.

As important molecules that regulate other cells,

it is important to understand the regulation of interleukins so as to create methods of controlling their production for medical purposes.

Continuation…


Activates resting T4-lymphocytes, B-lymphocytes, NK cells, polymorphonuclear leukocytes, endothelial cells, smooth muscle cells, and fibroblasts;

induces fever, sleep, anorexia and neutrophilia;

stimulates synthesis of proinflammatory cytokines and acute-phase proteins;

induces coagulation; stimulates the synthesis of collagen and collagenase for scar tissue formation;

Interleukin-1 (IL-1)


stimulates the synthesis of adhesion factors on endothelial cells and leukocytes for diapedesis;

activates macrophages; promotes

inflammation, and catabolic processes.

Produced by monocytes, macrophages, dendritic cells, and a variety of other cells in the body.

Continuation…


1. A growth and differentiation factor for activated T4-lymphocytes, T8-lymphocytes, B-lymphocytes, and NK cells;

2. promotes antibody secretion by B-lymphocytes;

3. induces the synthesis of other cytokines such as interferon-gamma and TNF-beta;

4. activates cytotoxic T-lymphocytes, NK cells, and monocytes/macrophages.

5. Produced primarily by activated T4-lymphocytes.



Supports the growth of multilineage bone marrow stem cells; a growth factor for mast cells.

Produced by activated T-lymphocytes, NK cells, and other cells.



A growth and differentiation factor for activated B-lymphocytes and activated T-lymphocytes; promotes production of TH2 cells and IgE by B-lymphocytes; enhances macrophage antigen processing and presentation activity; induces other cytokine production; induces immunoglobulin class shift in B-lymphocytes a growth factor for mast cells. Produced by TH2 cells as well as other cells.




Stimulates the proliferation of activated B-lymphocytes and their differentiation into plasma cells; stimulates antibody secretion and immunoglobulin class shift; induces growth and differentiation of eosinophils. Produced primarily by TH2 cells.


Functions similarly to interleukin-1 for redundancy in biological activities. Produced by many cells including T-lymphocytes, macrophages, and monocytes.




A chemokine (def); chemotactic for neutrophils; activates and triggers extracellular killing by neutrophils; enhances adherance of phagocytes to endothelial cells and diapedesis. Produced by monocytes, macrophages, and other cells.



A multifunctional cytokine that modulates the function of many immunocompetent cells, including T-lymphocytes, B-lymphocytes, NK cells, monocytes/macrophages, and neutrophils. Produced by T- and B-lymphocytes.


Activates TH1 induction and maturation; activates interferon-gamma production; enhances the cytolytic activity of CTLs, NK cells, and macrophages. Produced primarily by monocytes/macrophages and dendritic cells.



IL-1 and IL-18

Potent inflammatory effects, especially IL-1 & IL-1. IL-18 induces IF-, thus bridgingInflammatory & innate/adaptive immune responses. IL-1 induces TNF, IL-6 as well asInflammatory mediators from various cells, notably cells at the interface of the environment. IL-1 self-regulates through induction of IL-1Ra & IL-10. IL-1 is anendogenous pyrogen (fever inducer).

IL-1 & IL-18 Receptors

There are two receptors for each (RI and RII), both of which are members of the Ig supergene family. IL-1RI is found on the T and B cells, fibroblasts, keratinocytes, endothelial cells, chondrocytes, hepatocytes, and synovial lining cells and has a MW of 80 kDa. IL-1RII is found on B cells, neutrophils, and bone- marrow cells and has a MWof 60 kDa. The difference in MW arises from IL-1RII having a shorter cytosolic region. There is some evidence that these two receptors can mediate different biological events even though they both bind the two ILs. A 3rd non-signaling receptor is foundas well, possibly with regulatory function.

RI


IL-1

Signal (bacterial, etc.) to Monocyte, epithelium, etc.

IL-1

IL-6 TNF-

Req. for Ig class Dendritic cell maturation switching

Very enhanced Ag pres. to T cellsHigher avidity Ab response T cell effector functions:

TH1 TH2----B cells make Ab CTL Monocyte can be macrophage in blood or tissue.

IL-18

Signal (bacterial, etc.) to Monocyte

IL-18

IF-

MHC Class I & II, IL-18

Enhanced Ag pres. to T cells

T cell effector functions: TH1 TH2----B cells make Ab CTL


Chemokines are a group of cytokines that mobilize white blood cells (WBCs) to sites of inflammation. They pull the WBCs out of the bloodstream and chemotactically attract them to the inflammatory site, trigger some WBCs to release their killing agents for extracellular killing, and induce some WBCs to ingest the remains of damaged tissue. Certain chemokines have also been shown to suppress HIV, probably by binding to the chemokine receptors serving as the second binding factor for HIV on CD4+ cells. Examples of chemokines include IL-8, MIP-1a, MIP-1b, MCP-1, MCP-2, MCP-3, GRO-a, GRO-b, GRO-g, RANTES, and eotaxin.

When produced in excess amounts, chemokines can lead to damage of healthy tissue as seen in such disorders as rheumatoid arthritis, pneumonia, asthma, adult respiratory distress syndrome (ARDS), and septic shock.

Other Chemokines (DEF )


Interferons (IFN)

Interferons modulate the activity of virtually every component of the immune system.

Type I interferons include more than 20 types of interferon-alpha, interferon-beta, interferon omega, and interferon tau. - Type I interferons, which can be produced by virtually any virus-infected cell is better able to induce viral resistance in cells

There is only one type II interferon, interferon-gamma., where as type II interferon is produced by activated T-lymphocytes as part of an immune response and functions mainly to promote the activity of the components of the cell-mediated immune system such as CTLs, macrophages, and NK cells.


1. tumor necrosis factor-alpha (TNF-alpha; cachectin)

TNF is a potent mediator of inflammatory and immune functions. It is cytotoxic for some tumor cells;

induces fever and sleep; stimulates the synthesis of cytokines; stimulates the synthesis of collagen and

collagenase for scar tissue formation; stimulates the synthesis of adhesion factors on

endothelial cells and leukocytes for diapedesis;

Tumor necrosis factors


activates macrophages; promotes inflammation and catabolic processes; a

chemoattractant for phagocytes and promotes neutrophil degranulation;

responsible for endotoxin-induced septic shock; triggers apoptosis. Produced by monocytes/macrophages, TH1 cells, and other cells.

2. tumor necrosis factor-beta (TNF-beta; lymphotoxin)

Carries out many of the same activities as TNF-alpha. Produced primarily by TH1 cells and B-lymphocytes.

Continuation…


Interaction of Nervous, Endocrine & Immune Systems

Figure 24-21: Model for

interaction between nervous,

endocrine, and immune systems


V. Brusic, 2004

The immune system (IS)

protects organisms from pathogens cellular/humoral IS present in higher vertebrates protects from tumors helps the maintenance of homeostasis initiates and regulates immune responses

consists of organs, cells, and molecules involved in growth and regulatory processes adaptive learning system robust and largely redundant has combinatorial properties involves huge number of experiments


V. Brusic, 2004

Continuation… Major histocompatibility (MHC) molecule, which is a key for initiation and regulation ofimmune responses, discovered in 1986.

More than 1000 variants identified for each class I and class II MHC in humans (HLA).

Each individual has 3-6 class I HLA moleculesand more than that of class II molecules.


Innate/Acquired Dialogue(Introduction )

As the CD4+ Cell illustrates, no matter how important any single part of the Immune System may be, none is effective, if it is unable to communicate with the whole.

It is the synergy of the combined Immune System, not the potency of any one element, which makes it so capable a defender.

This fact, has lead to the study of the various ways the Immune System interacts with itself and its environment. Although an enormous amount of work remains in this area, we have already learned a great deal.


First.…

A number of chemicals produced by damaged cells and destroyed MicroOrganisms, known as Heat Shock Proteins, are also responsible for activating the Immune System.

This fact has been crucial to understanding, how the Immune System can respond to *damage* and *foreign*. Heat Shock Proteins activate both innate and specific elements, increasing Immune activity around the infection. (See: β-crystallin


Cytokines produced by Non-Specific Cells clearly affect the activities of the Acquired Immune System and vice versa.

The Cytokine environment is very important in determining what kind of response is made, and its effectiveness.

Many Parasitic Diseases owe their success to their ability to induce the production of Cytokines, which lead to a response that is not harmful to the Parasite.

It also seems that the initial cells to respond to an infection, determine the future course of the response.

Natural Killer Cells may respond to an infection by producing one Cytokine, while Macrophages would produce another.

The knowledge that the initial site of infection is critical, has lead to the development of more effective vaccine adjuvants and inoculation methods.

Second…


The Acquired Immune System appears to impart a degree of Specificity upon its innate brethren, through the use of a specific Surface Receptor for ImmunoGlobulin.

This receptor enables Macrophages and CD8+ Cells to use Ig's secreted by B-Cells, to recognize specific foreign factors.

The "network" theory of Immune regulation, suggests an even larger role for Ig - that AntiBody to AntiBody communication is responsible for the activation and eventual suppression of some Immune responses.

In summary, while it is convenient for descriptive purposes to break the Immune System into Innate and Acquired branches, which themselves can be further sub-divided, this is a somewhat artificial division.

Both branches influence each other and are in turn shaped by their environment.

Third…

vaccines

A vaccine is a biological preparation used to establish or improve immunity to a particular disease

Vaccines can be prophylactic or therapeutic Prophylactic vaccines prevent or ameliorate the

effects of a future infection by a pathogen Therapeutic vaccines may provide cure to the

existing pathologic state, such as cancer


Killed organisms as vaccines

Simplest way to destroy the ability of microbes to cause disease yet maintain their antigenesity is to prevent their replication by killing in an appropriate manner.

The inactivated microorganisms generally provides safe antigens for vaccination e.g. typhoid, cholera and poliomyelitis.

Care has to be taken to ensure that important protective antigens are not destroyed in the activation process.


Live attenuated organisms as vaccines Live microorganisms are cultivated under conditions that

disable their virulent properties or use closely related but less dangerous to produce broad immune response.

Attenuated organisms typically provoke more durable immune response as the replication of the living microbes confront the host with a larger and sustained dose of antigen

Another significance is that immune response takes place largely at the site of the natural infection.

Immunization using the attenuation method include yelow fever, measles, mumps, and rubella


Classical method s of attenuation

The objective of attenuation can be equally well attained using strains which are virulent for another species but avirulent in man. Example includes the use of cow pox to protect from small pox

Attenuation can be achieved by modifying the conditions under which an organism grows. Production of live but non-virulent forms of chicken cholera bacillus and anthrax can be achieved by growing the cultures at high temperatures and under anaerobic conditions.

Mycobacterium tuberculosis can be attenuated by adding the bile to the culture medium

Attenuation by cold adaptation of influenza and other respiratory viruses seems possible


Attenuation by recombinant DNA technology

Genetic recombination is being used to develop various attenuated strains of viruses such as influenza with lower virulence in man and some with increased multiplication rate in eggs

This new approach termed ‘ infection- permissive immunization’, utilizes parenteral administration of a recombinant virus which bears the relevant neuraminidase but an irrelevant haemaglutinin: the partial immunity so produced still permits natural infection but prevents the development of disease, and it is anticipated that this process will establish an effective resistance to subsequent contact with the virus



Development of avian flu vaccine by recombinant DNA technology

Use of viral vectors for other genes

This method employs the use of a virus as a ‘ piggy- back’ for genes from another virus that cannot be grown successfully, or which is inherently dangerous

Large DNA viruses such as vaccinia can act as carriers for one or many foreign genes while retaining infectivity for animals and cultured cells and the proteins encoded by these genes are appropriately expressed with respect to glycosylation and secretion by the infected cells

A wide variety of genes has been expressed by vaccinia virus vectors and demonstrated that the products of genes coding for viral envelop proteins such as influenza virus glycoprotein, HIV-I gp120 and herpes simplex virus glycoprotein D, could be correctly processed and inserted into the plasma membrane of infected cells.


Adjuvants

Adjuvant by definition is a substance incorporated into or injected simultaneously with antigen which potentiates the immune response. There are different modes of action of adjuvants

Depot effects- Free antigen usually disperses rapidly from the local tissues draining the injection site. The adjuvant counteract this by providing a long lived reservoir of antigen, either at an extracellular location or within macrophages.

The most common types of adjuvants of this type are alluminium compounds and Freund’s incomplete adjuvant. Both types increase the antibody response but the emulsions tend to produce higher and far more sustained antibody levels


Macrophage activation

Under the influence of repository adjuvants, macrophages from granulomata which provide sites for interaction with antibody-forming cells.

The maintenance by the depot of consistent antigen concentrations ensures that as antigen-sensitive cells divide within the granuloma, their progency highly likely to be further stimulated by antigen

The activated macrophages are thought to act by improving immunogenecity through an increase in the amount of antigen on their surface and the efficiency of its presentation to lymphocytes and by the secretion of soluble stimulatory factors which influence the proliferation of lymphocytes..


New vehicles for antigen delivery

Recent interest centered on the use of small lipid membrane vesicles (liposomes) as agents for the presentation of antigen to the immune system.

Liposomes act as a storage vacuole within the macrophage or fuses with the macrophage membrane to provide a suitably immunogenic complex. Proteins anchored in the lipid membrane by hydrophobic means give augmented cell –mediated immunity

Another innovation is the ISCOM (immunostimulating complex), a matrix of a glycoside derived from the bark of Saponariauiloya molina. Viral proteins attached to the micellar form of the glycoside through hydrophobic interactions are highly immunogenic


Hypersensitivity

Hypersensitivity may be referred to as an excessive and heightened immune response in response to relatively large amounts of antigen resulting in gross tissue damage

There are 4 types of hypersensitivity viz. type I, II, III and V. The type IV hypersensitivity is referred to as delayed type sensitivity

Type I- anaphylactic hypersensitivity: Response involves intense constriction of the bronchioles and bronchi and generally there is contraction of smooth muscle and dilatation of capillaries.

Contraction of bronchioles is associated with an explosive degranulation of the mast cells which are responsible for the release of histamine and other mediators


Atopic allergy

Nearly 10% of the population suffer from allergies involving localized anaphylactic reactions to extrinsic allergens such as grass pollen, animal danders, faeces from mites and house dust

Interaction of allergen with cell-bound IgE in the bronchial tree, the nasal mucosa and the conjunctival tissues releases mediators of anaphylaxis and produce the symptoms of asthma or hay fever.

Contact of the food with specific IgE on mast cells in the gastro-intestinal tract may produce local reactions such as diarrhoea and vomiting.

There is a familial predisposition to the development of atopic allergy yet no association with specific HLA types has been established


Type II- Antibody dependent cytotoxic hypersensitivity

Where an antigen is present on the surface of a cell combination with antibody will encourage the demise of that cell by promoting contact with phagocytes

Cell death may occur either by reduction in surface charge, by opsonic adherence directly through the Fc, or by immune adherence through bound C3.

Cell death may also occur through activation of the full complement system up to C8 and C9 producing membrane damage.

Target cells coated with low concentrations of IgG antibody can be killed ‘non-specifically’ through an extracellular non-phagocytic mechanism involving non-sensitized lymphoreticular cells which bind to the target


Intraspecies type ii reactions

Of many different polymorphic constituents of the human red cell membrane, ABO blood groups form the dominant system. The antigenic groups A and B are derived from H substance by the action of glycosyl transferases encoded by A or B genes respectively

Antibodies to A or B occur when the antigen is absent from the red cell surface; thus a person of blood group A will possess anti-B and so on

Individual with blood group A will be tolerant to antigens closely similar to A and form cross-reacting antibodies capable of agglutinating B red cells; O individual will make anti-A and anti-B. On transfusion, mismatched red cells will be coated by the isohaemagglutinins and cause severe reactions


Rhesus incompatibility

The rhesus (Rh) blood groups form the other major antigenic system, the RhD antigen being of the most consequence for isoimmune reactions.

A mother with RhD negative group can be sensitized by red cells from a baby carrying RhD antigens (DD or Dd genotype). Reaction with the D antigen on red cell leads to their destruction giving haemolytic disease of the new born

Type II drug reactions: Drugs may become coupled to body components and thereby undergo conversion from a hapten to antigen which will sensitize certain individuals

With topically applied ointments, cell mediated hypersensitivity may occur


Type III immune-complex meadited hypersensitivity

Exposure of excess of antigen over a protracted period, persistent infection with a microbial organism, autoimmunity to self components and repeated contact with environmental agents can all give rise to acute inflammatory reactions

Chemotactic factors released will lead to an influx of polymorphonuclear leucocytes which begin the phagocytosis of the immune complexes

The proteolytic enzymes, kinin-forming enzymes and polycationic proteins which are released will of course damage local tissues and intensify the inflammatory responses.


Type IV – cell mediated hypersensitivity (delayed type)

This form of hypersensitivity is encountered in many allergic reactions to bacteria, viruses and fungi in the contact dermatitis resulting from sensitization to certain to certain simple chemicals and in the rejection of tranasplanted tissues.

Example includes the Mantoux teaction obtained by injection of tuberculin into the skin of an individul in whom previous infection with the micobacterium had induced a state of cell-mediated immunity

Unlike other forms of hypersensitivity delayed type reactivity can not be transferred from a sensitized to a non-sensitized individual with serum antibody

Transfer has been achieved in the human using viable white blood cells


Type V – Stimulatory hypersensitivity

Many cells receive instruction by agents such as hormones through surface receptors which bind the external agents. This combination may lead to allosteric changes in configuration of the receptor or of adjacent molecules which become activated and transmit the signal to the cell interior

The transformation of human T-lymphocytes by monoclonal antibodies to the T3 antigen; the production of cell division in thyroid cells by growth autoantibodies; the induction of pinocytosis by anti macrophage serum; and the mitogenic effect of antibodies to sea urchin eggs


Transplantation

The replacement of diseased organs by a transplant of healthy tissue has long been an objective , but has been frustrated by the uncooperative attempts by the body to reject grafts from other individuals

Few important terms Autograft: Tissue grafted back on to the original donor Isograft: Graft between synergeneic individuals such

as identical twins or mice of the same pure line strain Allograft: Graft between allogeneic individuals e.g. man

to man and one mouse strain to another Xenograft: Graft between xenogeneic individuals i.e.

transplantation between two different species


Rejection is immunological

If the reaction has immunological basis, the second contact with antigen would represent a more explosive event than the first and indeed the rejection of a second graft from the same donor is much accelerated

Specificity: Second set rejection is not the fate of all subsequent allografts but only of those derived from the original donor or a related strain.

Role of the lymphocytes Neonatally thymectomized animals have difficulty in rejecting skin grafts but their capacity is restored by injection of lymphocytes from a synergeneic normal donor, suggesting that T – cells are implicated


Continuation… Production of antibodies: After rejection, humoral

antibodies with specificity for the graft donor may be recognized. In humans donor strain thymocytes in place of sheep erythrocytes will often demonstrate the presence of antibody-forming cells in the lymphoid tissues of grafted animals

Genetic control of transplantation antigens The specificity of the antigens involved in graft rejection

is under genetic control. Genetically identical individuals such as mice of a pure strain or uniovular twins have identical transplantation antigens and grafts can be freely exchanged between them.


Continuation…

The Mendelian segregation of the genes controlling these antigens has been revealed by interbreeding experimetns between mice of different pure strains.

Since these mice breed true within a given strain and always accept grafts from each other, they must be homozygous for the transplantation genes.

In the mouse around 40 loci controlling the transplantation have been identified, the complex locus termed H-2 predominates in the sense that it controls the strong transplantation antigens which provoke intense allograft reaction


Additional consequences of H-2 incompatibility

MLR: When lymphocytes from strains of mice of different class II haplotype are cultured together, blast cell transformation and mitosis occurs, the T- cells of each population of lymphocytes reacting against class II determinants on the surface of the other population.

Cell- mediated lympholysis: The involvement of class II MHC antigens in the transplantation rejection has been observed as responder cells activated by the class II-induced MLR help in the generation of cytotoxic T-cells directed to the H-2D/K determinants.

Graft –vs-host reaction (g.v.h.): Unlike the normal transplantation reaction of the host against graft, the reverse, the so called graft -vs- host reaction takes place.


Continuation…

When competent T- cells are transferred from a donor to a recipient which is incapable of rejecting them, the graft cells survive and have time to recognize the host antigen and react immunologically against them

Complications of h.v.g. reaction in human include the fever, anaemia, weight loss, rash, diarrhea and spleenomegaly.

Mechanisms of graft rejection: Lymphocyte mediated rejection: Mononuclear cells with very

few polymorphs or plasma cells infiltrate the tissue. The dramatic effect of neonatal thymectomy in prolonging skin transplants and the long survival of grafts on children with thymic deficiency implicate the T-lymphocytes in these reactions


Continuation…

Role of humoral antibody: Hyperacute rejection occurs within minutes of

transplantation in individual with preexisting antibodies either due to blood group incompatibility or pre sensitization to class I MHC through blood transfusion

Acute early rejection occurring up to 10 days after transplantation is characterized by dense cellular infiltration and rupture of peritubular capillaries appearing to involve T-lymphocytes.

Acute late rejection, which occurs from 11 days onwards is caused by the binding of the antibody and complement to the arterioles and glomerular capillaries


Prevention of graft rejection

Matching tissue types on graft donor and recipient: Since MHC differences provoke the most vicious rejection of grafts, it is important to define antigen specificities. This includes tissue typing and determining the polymorphism of the HLA-system

Immunosuppressive drugs: Azathioprine, has preferential effect on T-cell mediated

reactions and competes with inosinic acid for enxymes concerend in the synthesis of guanylic and adenylic acids. It also inhibits the synthesis of 5-phophoribosylamine, the net result is inhibition of nucleic acid synthesis.

Methtrexate, through its action as a folic acid antagonist also inhibits synthesis of nucleic acids.


Continuation…

Cyclosporin A, penetrates antigen- sensitive T- cells in the G0 to G1 phase and selectively blocks the transcription of lymphokine mRNA

Clinical Experience in the transplantation: Corneal grafts survive without the need for

immunosuppression. Grafts of cartilage are also successful in the same way.

Kidney grafts, heart transplants, liver transplants and bone marrow grafting have all been successfully carried out


The spectrum of autoimmune diseases

At one end of the spectrum lies the organ specific diseases with organ-specific antibodies. Hashimoto’s disease is an example, where there is production of circulating antibodies specific for thyroid constituents

Center of the spectrum was occupied by the disorders where the lesion tends to be localized to a single organ but the antibodies are non organ specific. Typical example is primary biliary cirrhosis, where antibodies present are mitochondrial specific but are not liver specific

At the end of the spectrum are non-organ specific diseses including systemic lupus arythematosus, where lesions and antibodies are not confined to any one organ


Genetic factors in autoimmune diseases

Autoimmune phenomena tend to aggregate in certain families, the first degree relatives of patients with Hashimoto’s disease show a high incident of thyroid autoantibodies.

In Pernecious anemia patients gastric parietal cell antibodies are prevalent in the relatives

Thyroid autoantibodies are more prevalent in ovarion dysgenesis having X-chromosome aberrations such as XO and particularly the iso-chromosome X abnormality.

There are strong associations between several autoimmune diseases and particular HLA specificities, e.g. DR3 in Addison’s disease and DR4 in rhematoid arthritis.


Etiology of autoimmune responses

Autoimmunity might arise by several mechanisms involving bypass of key T –inducer cells

Alternatively a regulatory defect may play a role in the autoimmune response. This could occur through an inability of the central T- inducer cell to respond to or induce T- suppressors.

Defects in the antigen specific, idiotype specific and non-specific T-suppressor systems may lead to autoimmune response

Other possibilities would be a stimulation of contrasuppressor cells, and the depression of class II genes


Pathogenesis of autoimmune diseases

Antibodies to erythrocytes and platelets and shorten the half-lives of these cells and transplacental passage of platelet antibodies produces a transient neonatal thrombocytopenia

Different thyroid autoantibodies can cause tissue destruction, stimulation or suppression of thyroid hormone production and stimulation or suppression of thyroid cell division

Spontaneous thyroiditis, diabetes, haemolytic anemia and lupus have all been observed in pure bred animal strains and the importance of autoimmunity for pathogenesis is shown by the amelioration of symptoms whenever the immune response is suppressed


Immunodeficiency diseases

Deficiencies of innate immune mechanismsPhagocytic cell defects: In chronic granulomatous disease the monocytes and

polymorphs fail to produce reactive oxygen intermediates due to a defect in the ctochrome b-245 normally activated by phagocytosis.

Polymorphs from granulomatous patients readily take up catalase positive staphylococci in the presence of antibody and complement but fail to kill them intracellularly

Myeloperoxidase deficiency is associated with susceptibility to systemic candidiasis, while a defective polymorph response to chemotactic stimuli characterizes the lazy leucocyte syndrome


Complement system deficiencies

Defects in control proteins The importance of complement in defense against

infections is emphasized by the occurrence of repeated life- threatening infection with pyogenic bacteria in patient lacking factor I, the C3b inactivator

An inhibitor of active C1 is grossly lacking in hereditary angioedema and this can lead to recurring episodes of acute circumscribed non-inflammatory oedema mediated by a vasoactive C2 fragment

Deficiency of components of the complement pathway Failure to generate the classical C3 convertase through

deficiencies in C1r, C4 and C2 has been reported in small number of cases associated with high incidence of SLE-like syndromes


B – cell deficiency

In Bruton’s congenial a –γ –globulinaemia, the production of immunoglobulin in affected males is grossly depressed and there are few lymphoid follicles or plasma cells in lymph node biopsies

The most common form of immunodeficiency late onset hypogammaglobulinaemia is characterized by recurrent respiratory infections is associated with low IgG levels

T – cell deficiency The DiGeorge and Nezelof syndromes are characterized

by a failure of the thymus to develop properly, consequently, stem cells cannot differentiate to become T –lymphocytes and the thymus dependent areas in lymphoid tissue are sparsely populated


Continuation…

Cell-mediated immune responses are undetectable and although the infants can deal with common bacterial infections they may be overwhelmed by vaccinia or measles or by BCG

Selective T- cell depression can arise from deficiency in the enzyme, purine nucleoside phosphorylase. The poor T –cell responses make these patients especially susceptible to infection with varicella and vaccinia viruses

Cell mediated immunity is depressed in immunodeficient patients with ataxia telangiectasia or with thrombocytopenia and eczema. In both conditions about 10% of the patients have died of malignancies of the lymphoid system or epithelial tumors


Stem cell deficiency

Without proper differentiation of the common lymphoid stem cell, both T- and B- lymphocytes will fail to develop and there will be a severe combined immunodeficiency of cellualr and humoral response

Secondary immunodeficiencyAcquired immunodeficiency syndrome (AIDS) AIDS results from infection of a human immunodeficiency

virus. Transmission of the disease is through infection with blood or semen containing the LAV/HTLV-VIII virus


Continuation…

LAV/HTLV-III is a member of the lentivirus group which cause destruction of the cells they infect

All are RNA retro viruses which utilize a reverse transcriptase to convert their genetic RNA into the corresponding DNA which is integrated into the host cell

The T4 (CD4) molecule on helper-inducer T –cell is the surface receptor which enables the AIDS virus to bind to and infect lymphocytes. This results in a drastic and complete destruction of the helper cell population

The consequences for cell- mediated immune responses as exemplified by the depressed dilated type skin reactivity to common antigens and the failure to produce cytomegalovirus-specific cytotoxic T-cells are quite devastating


The control of AIDS

After inadvertent transfusion of infected plasma, the first antibodies to appear are directed to the p110 envelop glycoprotein; antibodies to core proteins p25 and 18 may be seen later

Most antibodies are non-neutralizing in that they fail to prevent infection of susceptible cells in culture and in rare instances when they are neutralizing, the titers are low

If the molecule concerned in binding to the T4 on the helper cells is fashioned after MHC class II which also recognizes T4, it may be difficult if not impossible to produce an immune response to it because of self tolerance


Continuation…

The reverse transcriptase enzyme ought to be a good target for anti-viral therapy with drugs like suramin and ribavarin


by dr nasser al-daghri1 444 bchimmunology by nasser m. al-daghri, ph.d assistant professor college...

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