es/classes/genbio%20ch43_lecture.ppt" classchapter 43

Copyright © 2005 Brooks/Cole — Thomson Learning

Biology, Seventh Edition Solomon • Berg • Martin

Chapter 43

Internal DefenseInternal Defense


Biology, Seventh Edition CHAPTER 43 Internal Defense

• Immunology• Study of internal defensive

responses

• Immune response• Recognizing foreign or

dangerous macromolecules

• Responding to eliminate them



Human immune response



• Nonspecific immune responses• Provide general and immediate

protection–Pathogens

–Some toxins and drugs

–Cancer cells



• Specific immune responses• Highly specific

• Include immunological memory



• Antigen• Molecule specifically recognized

as foreign or dangerous by cells of the immune system

• Antibodies• Highly specific proteins that

recognize and bind to specific antigens



• Invertebrate immune responses• Always nonspecific

• Physical barriers–Cuticle

–Skin

–Mucous membranes



• Phagocytosis

• Antimicrobial peptides–Soluble molecules that destroy

pathogens



Phagocytosis



• Vertebrate nonspecific immune responses• First-line defenses

–Physical barriers

–Skin

–Mucous linings of the respiratory and digestive tracts

• Other nonspecific defenses



• Soluble molecules important in immune responses• Antimicrobial peptides

• Regulatory peptides

• Proteins that destroy pathogens



• Cytokines• Signaling proteins that regulate

interactions between cells

• Interferons–Inhibit viral replication and activate

natural killer cells



• Interleukins–Help regulate interactions between

lymphocytes and other cells of the body

–Some have widespread effects



• Chemokines–Attract, activate, and direct the

movement of certain cells of the immune system

• Tumor necrosis factors (TNFs)–Kill tumor cells and stimulate

immune cells to initiate an inflammatory response



• Complement proteins• Enhance the inflammatory

response–Lyse the cell wall of pathogens

–Coat pathogens, enhancing phagocytosis

–Attract white blood cells to the site of infection



• Phagocytes destroy bacteria• Neutrophils• Macrophages

• Natural killer cells (NK cells)• Destroy cells infected with viruses• Destroy foreign or altered cells

such as tumor cells



• Inflammatory response• Triggered when pathogens

invade tissues

• Vasodilation–Increased blood vessel diameter



• Increased capillary permeability–Allows fluid and antibodies to leave

the circulation and enter the tissues

• Increased phagocytosis



• In response to tissue injury, several types of molecules in the plasma that mediate inflammation are activated

• Mast cells release histamine and other compounds that cause vasodilation and increased capillary permeability



• Cell-mediated immunity• Specific T cells are activated

• Proteins released that destroy cells infected with viruses or other intracellular pathogens



• Antibody-mediated immunity• Specific B cells are activated

• Multiply and differentiate into plasma cells, which produce antibodies



• Immune system cells• Lymphocytes

–Develop from stem cells in the bone marrow

–T cells

–B cells

• Antigen-presenting cells (APCs)



Lymphocytes and antigen-presenting cells



• T cells• Responsible for cell-mediated

immunity

• T cytotoxic cells (TC cells)

• T helper cells (TH)

• Memory T cells



• Distinguished by T-cell receptors (TCRs)

• Thymus gland confers immunocompetence on T cells by making them capable of distinguishing between self and non-self



• B cells• Responsible for antibody-

mediated immunity

• Differentiate into plasma cells–Produce antibodies



• Some activated B cells become memory B cells–Continue to produce antibodies

after an infection has been overcome



• Antigen-presenting cells (APCs)• Display foreign antigens as well

as their own surface proteins

• Macrophages

• B cells



• Dendritic cells–Located in tissues that interact with

the environment

–Specialized to process, transport, and present antigens



• Major histocompatibility complex (MHC)• Immune responses depend on a

group of genes that encode MHC proteins

• Class I MHC genes–Encode self antigens, glycoproteins

expressed on the surface of most nucleated cells



• Class II MHC genes–Encode glycoproteins expressed on

APCs of the immune system

• Class III MHC genes–Encode components of the

complement system and TNFs



• Cell-mediated immunity process• Specific T cells are activated by a

foreign antigen–MHC complex on the surface of an infected cell

• A co-stimulatory signal and interleukins are also required

• Activated TC cells multiply, giving rise to a clone



• Clone cells migrate to the site of infection

• Pathogen-infected cells destroyed• Activated TH cells give rise to a

clone of TH cells• Clone cells secrete cytokines• B cells and macrophages activated



• Antibody-mediated immunity process• B cells are activated when they

combine with antigen• Activation requirements

–APC (dendritic cell or macrophage) with a foreign antigen–MHC complex displayed on its surface

–TH cell that secretes interleukins



• Activated B cells multiply, giving rise to clones of cells

• Cloned cells differentiate, forming plasma cells

• Plasma cells produce specific antibodies, immunoglobulins (Ig), in response to the specific antigens that activated them



• An antibody combines with a specific antigen to form an antigenantibody complex–May inactivate the pathogen

–Stimulate phagocytosis

–Activate the complement system



• Antibody structure• Y-shaped

• Two arms combine with antigen



Antigen-antibodycomplex



• Antibody molecule• Four polypeptide chains

–Two identical heavy chains

–Two shorter light chains

• Chain regions–Constant (C) region and

–Variable (V) region



• Recombination of DNA segments• Main factor responsible for

antibody diversity

• Occurs during the differentiation of B cells

• Millions of different types of B (and T) cells are produced



• Immunological memory• Memory B and memory T cells

remain in the body after an infection

• Responsible for long-term immunity



Immunological memory



• Primary immune response• Stimulated by the first exposure

to an antigen

• Secondary immune response• Stimulated by a second exposure

to the same antigen

• More rapid and more intense than the primary response



• Active immunity• Develops as a result of exposure

to antigens

• May occur naturally after recovery from a disease

• May be artificially induced by immunization with a vaccine



• Passive immunity• Temporary condition

• Develops when an individual receives antibodies produced by another person or animal



• Response to cancer cells• NK cells, macrophages, and

T cells recognize antigens on cancer cells and launch an immune response against them

• Cancer cells evade the immune system by blocking TC directly or by decreasing their class I MHC molecules



Cancer cell destruction



• Human immunodeficiency virus (HIV)• Retrovirus

• Causes acquired immunodeficiency syndrome (AIDS)

• Destroys T helper cells

• Severely impairs immunity



HIV-infected T cell



• Graft rejection• Transplanted tissues have MHC

antigens

• Immune response stimulated

• T cells destroy the transplant



• Hypersensitivity reactions• Rh incompatibility

• Allergic reactions

• Autoimmune diseases



• Rh incompatibility• Rh-negative woman gives birth to

an Rh-positive baby

• Anti-D antibodies develop

• Rh incompatibility occurs in future pregnancies



Rh incompatibility



• Allergic reaction• Allergen stimulates the

production of IgE

• IgE combines with receptors on mast cells



• Mast cells release histamine and other molecules–Causes inflammation, other allergy

symptoms

• Systemic anaphylaxis–Rapid, widespread allergic reaction

–Can lead to death



Allergic reaction

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