PLANTS, INVERTEBRATES, AND VERTEBRATES HAVE MULTIPLE,

NONSPECIFIC IMMUNE RESPONSES

Plants and animals have a variety of chemical defenses against infections

that affect dynamic homeostasis.

Fig. 43-2

INNATE IMMUNITY

Recognition of traitsshared by broad rangesof pathogens, using asmall set of receptors

•

•Rapid response

•Recognition of traitsspecific to particularpathogens, using a vastarray of receptors

•Slower response

ACQUIRED IMMUNITY

Pathogens(microorganisms

and viruses)

Barrier defenses:SkinMucous membranesSecretions

Internal defenses:Phagocytic cellsAntimicrobial proteinsInflammatory responseNatural killer cells

Humoral response:Antibodies defend againstinfection in body fluids.

Cell-mediated response:Cytotoxic lymphocytes defendagainst infection in body cells.

Innate Immunity

Innate immune responses are active immediately upon infection are the same whether or not the pathogen has been encountered previously

Innate immunity includes: Barrier defenses such as skin, mucous membranes, &

secretions Internal defenses such as phagocytic cells,

antimicrobrial proteins, inflammatory response & natural killer cells

Plants

Epidermis is a plants first line of defense (or periderm in woody plants)

If a pathogen successfully infects a plant cell, the plant can recognize invading pathogens and defend against them by chemical attack

Hypersensitive response – upon infection by some pathogens a signal transduction pathway triggers a programmed death to infected cells

PlantsSystemic Acquired Resistance: localized and specific; a containment response based on gene-for-gene recognition between host and pathogen

Methylsalicyclic acid is carried throughout the plant via the phloem; at the site of the infection it is converted to salicylic acid which activates signal transduction to produce proteins to resist pathogen attach

Invertebrates

Only form of defense is Innate ImmunityBoundary defense:

Outer boundaries (i.e. exoskeleton or skin) 1st line of defense Lysozyme – enzyme found in gut; digest microbial cell walls Low pH – further protects digestive system

Internal defense: phagocytic cells (hemocytes) engulf and destroy invaders Secreting cells are triggered by signal transduction

pathways to produce chemicals (including antimicrobial peptides) that kill, trap and/or inactivate microbes

Fig. 43-3

Microbes

PHAGOCYTIC CELL

VacuoleLysosomecontaining enzymes

Vertebrates

Barrier Defenses: skin and mucous membranes block entry

Mucous traps microbes and cilia sweep it away

Saliva, tears and mucus: contain lysozyme to destroy and wash away microbes

Acidic environment of stomach, skin and sweat prevent growth of microbes

Vertebrates

Cellular Defenses: Toll-like receptors (TLR) – membrane receptors recognize

components found in microbes; upon contact with microbe TLR trigger a series of internal defenses beginning with phagocytosis

Phagocytic cells include – NEUTROPHILS - most abundant; engulf and destroy microbes

MACROPHAGES – “big eaters;” large cells that migrate through the body or permanently reside in certain organs; well positioned to fight microbes

ESINOPHILS – defend against multi-cellular invaders (i.e. parasitic worms) by releasing destructive chemicals

DENDRITIC cells - stimulate acquired immunity against invaders

Vertebrates

Cellular Defenses Antimicrobial peptides and proteins

INTERFERONS – secreted by virus infected body cells inducing nearby uninfected cells to produce substances that inhibit viral reproduction (LIMIT CELL TO CELL SPREAD)

COMPLEMENT SYSTEM – roughly 30 proteins found in blood plasma; circulate in an inactive form; upon contact with microbes they become active; activation involves a series of actions that results in the lysis of the invading cells

NATURAL KILLER CELLS – target and destroy cells that have been infected; preventing spread of disease to healthy cells

Vertebrates

Inflammatory Response: changes brought about by signaling molecules

released upon injury or infection

Mast Cells – connective tissue cells that store chemicals for secretion

Histamine is released by mast cells at sites of damage triggers blood vessels to dilate and become permeable

Activated macrophages release more signaling molecules to further increase blood flow

Increased blood supply causes redness, heat & swelling

Antimicrobrial proteins , complement systems, phagocytes, etc… arrive via blood stream to destroy the invader which results in the accumulation of pus (fluid of WBC, dead microbes, & cell debris)

MAMMALS USE SPECIFIC IMMUNE RESPONSES TRIGGERED BY NATURAL OR

ARTIFICIAL AGENTS THAT DISRUPT DYNAMIC HOMEOSTASIS

Plants and animals have a variety of chemical defenses against infections that affect

dynamic homeostasis.

WHITE BLOOD CELLS CALLED LYMPHOCYTES RECOGNIZE AND RESPOND

TO ANTIGENS, FOREIGN MOLECULES

LYMPHOCYTES THAT MATURE IN THE THYMUS ABOVE THE HEART ARE CALLED

T CELLS

LYMPHOCYTES THAT MATURE IN BONE MARROW ARE CALLED B CELLS

Acquired Immunity

Immune System

Tonsils and adenoids – protect by trapping germs that enter through your mouth and nose

Thymus – produces T-cells Spleen – filters blood looking for foreign

cells Bone Marrow – produces new RBC and

WBC from stem cells; where B-cells are formed

Appendix – may serve as a storehouse for “good” bacteria

Lymph – clear / white made of WBC – particularly lymphocytes

Lymph Nodes - found throughout the body help recognize and fight infections; contain B, T and other immune cells

Lymphatic vessels – mirror the blood stream so that it can send out immune cells when needed

Peyer’s Patches -oval elevated patches of closely packed lymph follicles on the mucosa of the small intestines.

Antigen ReceptorsAll antigen receptors on a single

lymphocyte recognize the same epitope, or antigenic determinant, on an antigen

B cells and T cells have receptor proteins that can bind to foreign molecules

Each individual lymphocyte is specialized to recognize a specific type of molecule

An antigen is any foreign molecule to which a lymphocyte responds

A single B cell or T cell has about 100,000 identical antigen receptors

B cells give rise to plasma cells, which secrete proteins called antibodies or immunoglobulins

Secreted antibodies, or immunoglobulins, are structurally similar to B cell receptors but lack transmembrane regions that anchor receptors in the plasma membrane

B cell receptors bind to specific, intact antigens

The B cell receptor consists of two identical heavy chains and two identical light chains

The tips of the chains form a constant (C) region, and each chain contains a variable (V) region, so named because its amino acid sequence varies extensively from one B cell to another

In infected cells, MHC molecules bind and transport antigen fragments to the cell surface, a process called antigen presentation

A nearby T cell can then detect the antigen fragment displayed on the cell’s surface

T cells bind to antigen fragments presented on a host cell

These antigen fragments are bound to cell-surface proteins called MHC molecules

MHC molecules are so named because they are encoded by a family of genes called the major histocompatibility complex

Clonal Selection

The binding of a mature lymphocyte to an antigen induces the lymphocyte to divide rapidly

This proliferation of lymphocytes is called clonal selection

Two types of clones are produced: short-lived activated effector cells and long-lived memory cells

Second Exposure

The first exposure to a specific antigen represents the primary immune response

During this time, effector B cells called plasma cells are generated, and T cells are activated to their effector forms

In the secondary immune response, memory cells facilitate a faster, more efficient response

Cell Mediated Response Humoral Response

involves activation and clonal selection of cytotoxic T cells

Specific immunity brought about by T cells; fights body cells infected with pathogens; promotes phagocytosis by other white blood cells

involves activation and clonal selection of B cells, resulting in production of secreted antibodies

Specific immunity brought about by antibody producing B cells; fights bacteria and viruses in body fluids

Mammalian Immune System

Helper T cells aid both responses

Fig. 43-16Humoral (antibody-mediated) immune response

B cell

Plasma cells

Cell-mediated immune response

KeyStimulatesGives rise to

+

+

++

+

+

+Memory B cells

Antigen (1st exposure)

Engulfed by

Antigen-presenting cell

MemoryHelper T cells

Helper T cell Cytotoxic T cell

MemoryCytotoxic T cells

ActiveCytotoxic T cells

Antigen (2nd exposure)

Secretedantibodies

Defend against extracellular pathogens by binding to antigens,thereby neutralizing pathogens or making them better targetsfor phagocytes and complement proteins.

Defend against intracellular pathogensand cancer by binding to and lysing theinfected cells or cancer cells.

+

+ +

Helper T Cells

A surface protein called CD4 binds the class II MHC molecule

This binding keeps the helper T cell joined to the antigen-presenting cell while activation occurs

Activated helper T cells secrete cytokines that stimulate other lymphocytes

Killer T CellCytotoxic T cells are the effector cells in cell-mediated immune response

Cytotoxic T cells make CD8, a surface protein that greatly enhances interaction between a target cell and a cytotoxic T cell

Binding to a class I MHC complex on an infected cell activates a cytotoxic T cell and makes it an active killer

The activated cytotoxic T cell secretes proteins that destroy the infected target cell

B CellsThe humoral response is characterized by secretion of antibodies by B cells

Activation of B cells is aided by cytokines and antigen binding to helper T cells

Clonal selection of B cells generates antibody-secreting plasma cells, the effector cells of humoral immunity

Antibodies: The five major classes of antibodies, or immunoglobulins, differ in distribution and function

Neutralization occurs when a pathogen can no longer infect a host because it is bound to an antibody

Opsonization occurs when antibodies bound to antigens increase phagocytosis

Antibodies together with proteins of the complement system generate a membrane attack complex and cell lysis

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