Biology 8: Immune System Structure Innate Immunity: Defenses that are always active but NONSPECIFIC. Skin, mucus, stomach acid, tears etc. Adaptive Immunity: Defenses that take time to activate and are SPECIFIC to the invader. Innate Immune System Non-cellular innate defenses: Skin: Physical barrier. Secretes antimicrobial enzymes like defensins Mucus: On mucous membranes. Traps pathogens. In respiratory system mucous is propelled upward by cilia via mucociliary escalator Lysozymes: In tears and saliva. Antimicrobial compound Complement Can punch holes in the cell walls of bacteria making them System: osmotically unstable, leading to lysis. Also triggers opsonization. Interferons: Given off by virally infected cells. Interfere with viral replication and dispersion Cellular innate defenses: Macrophages: Ingest pathogens and present them on MHC-II. Secrete Cytokines MHC-I:Present in all nucleated cells. Displays endogenous antigen to cytotoxic CD8+ T-cells. MHC-II:Present in professional antigen-presenting cells (macrophages, dendritic cells, some B-cells, and certain activated epithelial cells). Displays exogenous antigen to helper CD4+ T-Cells. Dendritic Antigen-presenting cells in the skin Cells: Adaptive Immune System Humoral Immunity: Centers on antibody production by B-Cells. Kills antigens while they are floating around in the fluid (humor). B-Lymphocytes Made and mature in bone marrow. Activated in spleen (B-cells): or lymph nodes. Express antibodies on its cell surface. Antibodies (Ig): Produced by plasma cells, which are activated B-Cells. Target an antigen. Contain 2 heavy chains and 2 light chains. Constant region & variable region. Tip of variable region is the antigen-binding region. Hypermutation: Mutation of the antigen binding site on an antibody. Results in varying affinities of antibodies for a specific microbe. 5 diff isotypes (IgM, IgD, IgG, IgE, IgA) Opsonization: Antibodies mark pathogens for destruction. Agglutination: Pathogens clump together into insoluble complexes. Caused by opsonizing pathogens. Memory B-Cells: Lie in wait for a second exposure to pathogen. Secondary response is more rapid and vigorous. Cell-Mediated (Cytotoxic) Immunity: Centers on T-Cells. Responds to cells once they have been infected by the antigen. T-Lymphocytes Made in bone marrow, mature in Thymus. Coordinate (T-cells): immune system and directly kill infected cells. Cellmediated immunity. Positive/Negative Maturation of T-Cells. Facilitated by thymosin. Occurs Selection: in Thymus. Positive Selection: Mature only T-cells that can respond to the presentation of antigen on MHC. Negative Selection: Causes apoptosis in T-cells that are self-reactive Helper T-Cells: Th or CD4+. Respond to antigen on MHC-II. Coordinate rest of the immune system, secreting lymphokines to activate immune defense. Th1 – secrete interferon gamma Th2 – activate B-Cells, in parasitic infections Cytotoxic T-cells: Tc, CTL, or CD8+. “Killer cells”. Respond to antigen on MCH-I and kill virally infected cells Natural Killer Attack cells low on MHC, including virally infected cells and Cells: cancer cells Suppressor T-Cells: Treg. Down regulate the immune response after an infection and promote self-tolerance. Defective Granulocytes: Neutrophils: Activated by bacteria, conduct phagocytosis. suppressor T-Cells lead to autoimmune conditions. Eosinophil: Activated by parasites & allergens !histamines Basophils: Activated by allergens, inhibit blood clotting. Memory T-Cells: Serve a similar function to memory B-Cells Autoimmune A self-antigen is recognized as foreign, and the Conditions: immune system attacks normal cells Lymphatic System • • • • • Circulatory system that consists of one-way vessels with intermittent lymph nodes Provides for mounting immune responses Connects to the cardiovascular system via the thoracic duct in the posterior chest Equalizes fluid distribution, transports fats and fat-soluble compounds in chylomicrons Edema results when the lymphatic system is overwhelmed and can’t drain excess fluid from tissues Allergic Reactions: Nonthreatening exposures incite an inflammatory response Immunization: Induces active immunity (activation of B-Cells that produce antibodes) Passive Immunity: Transfer of antibodies to an individual. Breast milk.