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Antigen presenting cells apcs engulf antigens and

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Antigen-Presenting Cells (APCs)Engulf antigens and present fragments of antigens to T cells for recognition42B cellsDo not activate naive T cellsPresent antigens to helper T cell to assist their own activationDendritic cellsFound in connective tissues & epidermis / act as mobilesentinels of boundary tissuesPhagocytize pathogens that enter tissues, then enterlymphatics to present antigens to T cells in lymph nodeMost effective antigen presenter known/ key linkbetween innate & adaptive immunityMacrophagesWidely distributed in connective tissues and lymphoid organsPresent antigens to T cells, which not only activates T cell, but also further activatesmacrophageActivated macrophagebecomes voracious phagocytic killerAlso trigger powerful inflammatory responses and recruit additional defenses
Humoral Immune ResponseWhen B cell encounters target antigen, it provokeshumoral immune responseAntibodies specific for that particular antigen are then producedB cells are activated whenantigens bind to surfacereceptors, cross-linking themReceptor-mediated endocytosisof antigen-receptor complexes(clonal selection)proliferationand differentiation of B cell intoeffector cells(plasma cell)antibody-secreting effector cellsSecrete specific antibodies at rate of 2000 mol. / se for 4 to 5 days, then dieAntibodies circulate in blood or lymph, binding to free antigens, marking them fordestruction by innate or other adaptive mechanismsActivation and Differentiation of B Cells
Clone cells that do notbecome plasma cellsbecomememory cellsProvideimmunologicalmemoryMount an immediateresponse to futureexposures to sameantigenHumoral Immune ResponseActivation and Differentiation of B Cells
Immunological MemoryPrimary immune response:cell proliferation and differentiation upon exposureto antigen for the first timeLag period: 3 to 6 daysPeak levels of plasma antibody are reached in 10 daysAntibody levels then declineSecondary immune responseRe-exposure to same antigengivesfaster, more prolonged, more effectiveresponseSensitized memory cells provideimmunological memoryResponse time hrs vs. daysAb levels peak faster 2 to 3d & athigher levelsAb bind with greater affinityAb level can remain high for wks tomonthsWhere do vaccines fit into this?
Active and Passive Humoral ImmunityB cellsencounterantigens &producespecificantibodiesagainst themready-madeantibodies areintroduced intobody
also calledImmunoglobulins(Igs)—are proteins secreted by plasma cells / make upgamma globulinportion of bloodCapable of binding specifically with antigen detected by B cellsAntibodies47Basic antibody structureOverall T- or Y-shaped antibody monomerconsists of four looping polypeptide chainslinked by disulfide bondsFour chains consist of:Two identical heavy (H) chains withhinge region at “middles”Two identical light (L) chainsVariable (V)regions atend of eacharm combine to form two identical

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