Microbiology Chapter 16 The Adaptive Immune Response A Glimpse of History Diphereria Infection that caused obstruction of the airway in small children Infected animals that recovered where re exposed to the antigen and showed no illness Discovery of antibodies in the blood Adaptive Immune Response 1 Primary response to particular antigen o o may take a week or more to develop o during this time innate immunity may may not suffice 2 Secondary anamnestic response later to same antigen immune system remembers antigen on subsequent exposure enhanced response Two Categories of Immune Defense Humoral immunity mediated by antibodies to eliminate extracellular antigens bacteria viruses toxins in fluids around tissues bloodstream antibodies can bind to the receptors stopping the cell from entering a body tissue or cell o o o o o o o Cellular immunity mediated by cells to eliminate intracellular antigens o o Ex viruses inside cells Types of Lymphocytes Cellular immunity eliminating intracellular antigens o mediated by T lymphocytes T cells o mature in thymus o o o o don t recognize free antigens outside the cell antigen must be presented on a host cell surfaceto T cell receptors similar to B cell receptors on T cell second opinion to T cells provided by dendritic cells innate immunity the APC 2 subsets of T cells eliminate antigen and form memory cells 3rd type regulatory T cells cytotoxic T cells killer cells helper T cells o prevent response against self i e auto immune diseases The Lymphiod System system of tissues and organs which bring B and T cells in close contact with antigens therefore stategically located in body lymph fluid formed as result of circulatory system oxygen rich nutrient rich fluid leaves blood filters into tissues most depleted fluid returns to bloodstream some collected by lymphatic system lymph lymph travels to lymph nodes where antigens and T and B cells make contact protein cells removed fluid portion empties back into bloodstream behind left collarbone where lymphocytes gather to encounter captured antigens MALT mucosal associated lymphoid tissue a network of lymphatic tissue Lymph nodes Spleen Tonsils Secondary Lymphoid organs o o o Ex Peyer s patches sample the small intestine which allow the presentation of an antigen to lymphocytes below the mucsal layer and transfer it to the cells beneath An important role in mucosal immunity the prevents microbes from invading mucus membranes SALT skin associated lymphoid tissues Lymphoid tissues under skin ONLY organs where adaptive response can be triggered thus their strategic locations in body Primary Lymphoid Tissues o o o o o o o o Also called imunoglobulins have two indentical arms Fab regions and the stem Fc region o Red bone marrow and the thyroid o Where the T and B cells mature The Nature of Antibodies Y shaped proteins Four protein chains held together by disulfide bonds 2 heavy 2 light undergo more frameshift mutations o o Each heavy and light chain has a Constant region fc o Each heavy and light chain has a Variable region Fab o Variable region unique binds a specific antigen Fab are antigen binding Fc are fragments that cen be crystallized Antibody Actions o Neutralization prevents toxin virus from binding to cell Immobilization prevention of adherence blocks function binding o Agglutination precipitation clumped bacteria more easily phagocytized o Opsonization o Complement is activated coated bacteria more easily phagocytized done by c3b compliments bound antibody triggers Classical pathway that triggers compliment cascade results in things like the membrane attack complex o Cellular cytotoxicity antibody Dependent cellular cytotoxicity cell carrying antibodies is a target for immune cells e g natural killer NK cells NK cells that directly kill the cell Immunoglobulin classes o All are monomers except for one which is a polymer Function of IgD is still not clear o IgM pentamer functions as part of B cell receptors which perform initial antigen binding Ten antigen binding sites that have a great chance at agglutination precipitation and nueralization IgG monomer most abundant Memory antibody that is passed into the womb in passive immunity IgG and IgM are most abundant provide majority of specific immune response to microbes IgA protects epithelial linings of tracts exposed to exterior of body directly neutralize toxins viruses block bacteria from binding host cells mucosal immunity that is a dimmer secretion and monomer serum IgE attracts eosinophils stimulates release of histamines by basophils and mast cells Involved in defense against parasitic worms and other multicellular parasites Stimulates the release of histamine by the stimulation of basophils and mast cells Nature of Antigens Ag Antibody generator immunogen any compound that elicits an immune response huge variety pathogenic bacteria and viruses toxins transplanted organs plant pollens o o In general o o proteins polysaccharides strongly antigenic lipids nucleic acids often not recognition is via antigenic determinant epitope o epitope short peptide sequence or a shape Clonal Selection of the Lymphocyte When antigen enters body only B cells making appropriate antibody can bind o clonal selection These cells proliferate extensively clonal expansion o o Without sustained stimulation B cells undergo apoptosis which limits the immune response a good thing Clonal selection theory is the theory that only the antigen binding cell will clone because it is needed B lymphocytes and the antibody response cellular immunity attacks the enemy cells directly B lymphocytes produce antibodies that bind to antigens and tag them for destruction by other means o Recognition phase o begins when an antigen binds to several surface receptors on immunocompetent B cell taken into the cell by receptor mediated endocytosis After endocytosis B cell processes digests the antigen Links the epitopes to its MHC II proteins and displays on surface These antigen specific receptors are identical to the same antigen specific antibody that the B cell will later release antigen help link together receptors B cell is now an APC Activation phase o a helper T cell activates a B cell by binding to the antigen MHC II protein complex on the B cell a few B cells can be directly activated by antigens alone o o Normally antigen alone can t activate a B cell by Th independent antigens can generate B cell production Ex LPS on gram neg o Most helper T cells can bind to APC B cells in lymph o