Chapter 20 Immunity Innate defenses Specific immunity Cell

Chapter 20: Immunity Innate defenses Specific immunity Cell mediated immunity Self recognition

Defense system

First line of defense: Surface membrane barriers p Skin and mucous membrane n n n p p p Layered epidermis and shedding of epithelial cells Sebum inhibits growth of bacteria and fungi. Mucous traps microbes, dust and pollutants. Lacrimal apparatus Saliva Vaginal secretions Flow of urine Defecation and vomiting Gastric juices destroy bacteria and their toxins

Second line of defense: chemical and cellular defenses p Antimicrobial proteins n n n Interferon Complement Transferrins Natural killer cells p Phagocytes p n n n Neutrophils Dendritic cells Macrophages Wandering p Fixed p n Eosinophils

Phagocytosis

Inflammatory response Prevents spread of damaging agents. p Disposes of cell debris and pathogens p Sets the stage for repair. p Characteristics p n n n Pain Redness Heat Swelling Impairment of function

Inflammatory response Prevent spread of damaging chemicals and pathogens p Dispose of cellular debris and pathogens p Set the stage for repair p Signs of inflammation p n n n Redness Heat Swlling Pain Impairment of function

Inflammation Stages of inflammation p Release of chemical alarms p Vasodilation and permeability of BV p Emigration of phagocytes p Tissue repair

Phagocyte mobilization

Interferons Produced by lymphocytes, macrophages and fibroblasts. p Interfere with translation of viral proteins p Degrade viral RNA p Activate macrophages and NK cells p

Complement

Adaptive Resistance Specificity—recognition of particular antigens p Memory—remembers previously encountered antigens p Systemic—immunity is not restricted to the initial infection site p Immune responses p n n Antibody-mediated or humoral immune responses (late 1800 s) Cell-mediated immune responses (mid 1900 s)

Antigens and antigen receptors Antigens can be entire microbes, parts of microbes or chemical components of pollen, egg white, blood cells, ……. p Complete antigens p n n p Immunogenicity Reactivity Incomplete antigens n n Haptens Epitopes

Self antigens: MHC proteins Antigens on our own cells are self-antigens p MHC proteins are glycoproteins that mark the cell as self. p n n Class I MHC proteins are on all body cells Class II MHC proteins are only on certain cells that act in the immune response

Immunocompetence p T and B cells that have not been exposed to an antigen are naïve. p Binding with an antigen completes differentiation into functional B and T cells.

Immunocompetence for T cells 1. 2. Must be able to bind MHC molecules. Must not react strongly to self antigens.

Antigen receptors Genes determine what foreign substance will be recognized. p An antigen determines which T or B cells will be activated. p Lymphocytes make over a billion different receptors. p Gene segments of a few hundred bits are reshuffled and combined--somatic recombination. p The newly assembled gene is expressed as a receptor on the cell surface. p

Humoral immune response Antigen challenge—the meeting between a naïve immunocompetent lymphocyte and an invading antigen. p Occurs in lymphoid tissue such as spleen or lymph node. p If antigen challenge is presented to a B cell then the humoral immune response is provoked. p

Immunological memory p Primary immune response p Secondary immune response

Antibodies

Immunoglobulin classes Ig. D is attached to B-cell plasma membrane p Ig. M is released during primary response p Ig. G functions in late primary and secondary response p Ig. A found in body secretions p Ig. E causes release of histamine p

Antibody defense: PLANe p Precipitation p Lysis: Complement fixation and activation p Agglutination p Neutralization p Enhancing phagocytosis

Complement

Cell-mediated immunity Antibodies can only inactivate an antigen and NOT destroy it. p Antibodies prepare an organism for destruction by innate defenses. p T cells can only recognize and respond to processed fragments of protein. p T cells are suited for cell to cell interaction and target body cells infected by virus, bacteria and abnormal or cancerous body cells or cells that are transplanted or infused. p

Cell-mediated immunity: T-cells Activation of T cells—T cell receptors bind to antigen presented by the antigen-MHC complex. p CD 4 and CD 8 proteins interact with antigen and help maintain MHC-antigen coupling. p Types of T-cells p n n n Helper T cells (CD 4) Cytotoxic T cells (CD 8) Memory T-cells

T cell activation p p p T cells must accomplish a double recognition. They must recognize nonself (antigen) and self (MHC protein of a body cell). Co-stimulation by binding to other proteins on APC Cytokines (IL 1 and 2) are released by APC or T cell following co-stimulation Antigen binding without co-stimulation leads to anergy in T and B cells. Antigen recognition and co-stimulation lead to activation.

Antigen-presenting cells

Antigen-presenting cells

Activated T cell Activation leads to enlargement, differentiation and proliferation of T cells. p T cells that are reproduced are clones of originally activated T cell. p Activation, differentiation and proliferation occurs in secondary lymph organs and tissue. p Activation leads to release of inflammatory cytokines. p

Cytotoxic T cells

Organ transplants Autografts—grafts from the same person to another body site p Isografts—grafts between genetically identical individuals p Allografts—grafts among the same species p Xenografts—grafts taken from another animal species p

Homeostatic imbalances of immunity: Immunodeficiencies p Severe combined immunodeficiency (SCID) syndromes p Acquired immune deficiency syndromes n n n Hodgkin’s Disease HIV AIDS

Homeostatic imbalances of immunity: Autoimmune disease Type I diabetes—destroys pancreatic beta cells p Multiple sclerosis—destroys myelin sheaths p Myasthenia gravis—impairs communication between nerve and muscle p Lupus erythematosus—systemic disease of skin, kidneys, heart, and lungs p Grave’s Disease—stimulates thyroid glad to make excessive amounts of thyroxine p Rheumatoid arthritis—destruction of joints p

Hypersensitivities