CH 21 THE IMMUNE SYSTEM

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1 CH 21 THE IMMUNE SYSTEM Several lines of defense exist for the human body to help ensure maintenance of homeostasis. Some are general in action and others are extremely specific. Overall, we say that two intrinsic defense systems (nonspecific and specific) act independently but cooperatively to facilitate body defense. 1 - NONSPECIFIC BODY DEFENSES A - FIRST LINE DEFENSES: SKIN AND MUCOUS MEMBRANES Skin Mechanical Barrier Keratin Mucous Membranes Mechanical Barrier Sebum HCl Saliva Lacrimal Fluid Lysozyme Cilia Hair B - SECOND LINE DEFENSES Five Nonspecific Defenses Inflammation Phagocytosis Natural Killer (NK) Cells Antimicrobial Proteins Fever Production 29

2 INFLAMMATION Inflammation triggered by injury to body tissues helps (1) prevent spread of invaders, (2) dispose of cell debris and pathogens, and (3) initiate mechanism for repair. Four Signs of Inflammation Redness Hyperemia Heat Hyperemia Swelling Edema Pain Possible Fifth Sign Impairment of Function Chemotactic Agents Sequence of Inflammation Leukocyte-Inducing Factors Leukocytosis Margination Pavementing Diapedesis Emigration Macrophage Activation Pus Formation Infectious Granulomas PHAGOCYTOSIS Stages of Phagocytosis Adhesion Phagosome Phagolysosome Exocytosis 30

3 Respiratory Burst Defensins Opsonization Types of Phagocytes Macrophages Histiocytes Fixed Free Neutrophils NATURAL KILLER (NK) CELLS Targets Self-cells Perforins ANTIMICROBIAL PROTEINS Various forms, including: 1 - Interferons 2 - Complement Fixation MAC Formation Several Pathways: Classical Alternative Properdin Lectin FEVER PRODUCTION Hypothalamus 31

4 Thermostat 98.6/36.2 Pyrogens SPECIFIC BODY DEFENSES: IMMUNITY (ADAPTIVE DEFENSE) This system recognizes specific foreign substances and acts to immobilize, neutralize, or destroy them. The goal: elimination of all pathogens. It must be primed by an initial exposure to the antigen (agglutinogen). Hence, lag-time before memory cell protection via antibody (agglutinin) production. Agglutinogen (Ags) Self Antigens MHC-Class I HLA MHC-Class II Non-Self Antigens Complete Antigens Haptens Agglutinin Antigenic Determinants The immune system is antigen-specific. It is systemic, not isolated to initial infection site. It is equipped with memory after initial attacks. There are several forms of immunity and they involve defensive T-cells and B-cells. T-cells cannot react to antigens in solution and B-cells cannot cross a cell membrane. That is why you need both. The T-cells defend against abnormal cells as well as antigens within cells and the B-cells defend against pathogens outside the cell that are within the body fluids. FORMS OF IMMUNITY Acquired Immunity Naturally Acquired 32

5 Artificially Acquired Active Immunity Passive Immunity CELL-MEDIATED IMMUNITY: THE ACTION OF T-CELLS Thymus Immunocompetent Thymosins Classification CD-4 CD-8 Alpha/Beta Gamma/Delta Five Types of T-Cells: These cells are classified based on function and on presence/absence of pair of cell differentiation glycoproteins displayed on membrane surface of the mature T-cell. Cytotoxic Perforins Lymphotoxins TNF Tumor Necrosis Factor Helper Lymphokines Adhesion Co-Stimulation Regulatory Formerly suppressor T-cells. Delayed Hypersensitivity Memory 33

6 ANTIGEN PRESENTING CELLS Antigen presenting cells (APC s) are mobile sentinels located throughout the body. T-cells and activated B-cells are antigen-presenting cells. Some other cells in the body that are non-lymphocytes are also antigen-presenters. APC s include dendritic cells (DC s) (like the epidermal Langerhans cells) and macrophages (including the Kupffer (stellate) cells of the liver and the microglia of the CNS). HUMORAL IMMUNITY (ANTIBODY-MEDIATED): THE ACTION OF B-CELLS B-cells originate in bone marrow. They mature and develop immunocompetence while in bone marrow. If an antigen encounters a B-cell and if they have mutually compatible receptors, they will bond. Mechanisms of antibody action: Neutralization Agglutination Precipitation Complement activation Clonal Selection: Plasma Cells Memory Cells THE ANTIBODIES (A/K/A: IMMUNOGLOBINS, Ig s, GAMMA GLOBULINS) These molecules constitute the gamma globulin portion of our plasma proteins. They each consist of four looping polypeptide chains that are linked by disulfide bonds. Antibody structure includes: Heavy Chain Light Chain Variable Chain Constant Chain 34

7 CLASSES OF ANTIBODIES IgD IgM IgG IgA IgE TRANSPLANTS Allografts Autografts Isografts Xenografts 35

8 DISORDERS-DISEASES AIDS Autoimmune diseases Glomerulonephritis HIV (human immunodeficiency virus) causes destruction of defensive helper T-cell white blood cells. Body turns against itself, fails to recognize own cells as self and attacks them. This causes inflammation and destruction. Severe impairment of renal function. Grave s disease Causes production of excessive amounts of thyroxin. Hashimoto s thyroiditis Juvenile diabetes mellitus (Type I) Multiple sclerosis Myasthenia gravis Rheumatoid arthritis Thyroglobin is released into bloodstream due to trauma to thyroid gland causing rupture of thyroid follicles. Released material regarded as a foreign object in blood stream and provokes immune response. Systematic autoimmune destruction of the beta cells of the pancreas. The myelin sheaths in the CNS are gradually destroyed and replaced with nonfunctional hardened sheaths called scleroses. Affects primarily skeletal muscles. Inhibits transmission of nerve impulses via ACh. Systematically destroys joints. Scleroderma Sjogren s syndrome Systemic lupus erythematosus (SLE) Hypersensitivities CT disease. Several forms, the systemic form can affect internal organs and can be fatal. Skin only is chronic, not fatal. Autoimmune inflammation of glands; leads to the development of dry eyes and mouth. Primarily females affected. Diagnosis via ANA (antinuclear antibody test). Butterfly rash across face = common symptom. Allergies, allergens, anaphylaxis, and anaphylactic shock. Sarcoidosis SCID Possibly autoimmune. Causes formation of granulomas in body organs. Often associated with lungs. A/k/a: severe combined immunodeficiency disease. Devastating congenital condition. Genetic defect causes lack of B-cells and T-cells for defense. 36