LE 43-12B cells thatdiffer inantigenspecificityAntigen moleculesAntigen receptorAntibody moleculesClone of memory cellsClone of plasma cellsLE 43-19Viral neutralization(blocks binding to hostand opsonization increasesphagocytosis)Agglutination ofantigen-bearing particles,such as microbesPrecipitation ofsoluble antigensActivation of complement systemand pore formationBinding of antibodies to antigensinactivates antigens byBacteriaSolubleantigensMACComplement proteinsForeign cellPoreVirusBacteriumEnhancesPhagocytosisMacrophageCell lysisLeads toLE 43-13Antibodiesto AAntibodiesto B Time (days)5649423528211470104103102101100Antibody concentration(arbitrary units)First exposureto ASecond exposureto A, first exposure to BLE 43-18eIgD(monomer)Present primarily on surface of naive B cells that have not beenexposed to antigensTransmembraneregionActs as antigen receptor in antigen-stimulated proliferation anddifferentiation of B cells (clonal selection)LE 43-18aJ chainIgM(pentamer)Promotes neutralization and agglutination of antigens; veryeffective in complement activation (see Figure 43.19)First lg class produced after initial exposure to antigen; then itsconcentration in the blood declinesLE 43-18bIgG(monomer)Promotes opsonization, neutralization, and agglutination ofantigens; less effective in complement activation than lgM (seeFigure 43.19)Only lg class that crosses placenta, thus conferring passiveimmunity on fetusMost abundant lg class in blood; also present in tissue fluidsLE 43-18cIgA(dimer)Provides localized defense of mucous membranes byagglutination and neutralization of antigens (see Figure 43.19)J chainSecretorycomponentPresence in breast milk confers passive immunity on nursinginfantPresent in secretions such as tears, saliva, mucus, and breast milkLE 43-18dIgE(monomer)Triggers release from mast cells and basophils of histamine andother chemicals that cause allergic reactions (see Figure 43.20)LE 43-20IgEAllergenGranuleMast cellHistamineLE 43-10Lymphoidstem cellBone marrowThymusT cellBlood, lymph, and lymphoid tissues(lymph nodes, spleen, and others)B cellLE 43-8Antigen-bindingsiteDisulfidebridgeLightchainVVCCCCVVAntigen-binding siteVariable regionsConstant regionsTransmembraneregionAntigen-binding siteCVCVPlasmamembraneT cellβ chainα chainDisulfide bridgeCytoplasm of T cellA T cell receptor consists of one αchain and one β chain linked by adisulfide bridge.A B cell receptor consists of two identical heavychains and two identical light chains linked byseveral disulfide bridges.Heavy chainsCytoplasm of B cellB cellLE 43-9Antigen-presentingcellAntigenfragmentClass II MHCmoleculeT cellreceptorHelper T cellAntigenfragmentClass I MHCmoleculeT cellreceptorCytotoxic T cellInfected cellMicrobeLE 43-16PeptideantigenTargetcellClass I MHCmoleculeTCRCD8GranzymesPerforinCytotoxic T cellPoreApoptotictarget cellReleasedcytotoxicT cellCytotoxicT cellCancer cellLE 43-15DendriticcellBacteriumPeptide antigenClass II MHCmoleculeTCRCD4Helper T cellB cellCytokinesCytotoxic T cellCell-mediatedimmunity(attack oninfected cells)Humoralimmunity(secretion ofantibodies byplasma cells)DendriticcellLE 43-17MacrophageClass II MHCmoleculeBacteriumPeptideantigenCD4TCRHelper T cellActivatedhelper T cellCytokinesClone of memoryB cellsEndoplasmicreticulum ofplasma cellClone of plasma cellsSecreted antibodymoleculesB cell+LE 43-14_3First exposure to antigenAntigens engulfed anddisplayed by dendritic cellsActivateHumoral immune responseCell-mediated immune responseHelperT cellActive andmemoryhelperT cellsGives rise toAntigens displayedby infected cellsActivateCytotoxicT cellMemorycytotoxicT cellsGives rise toSecretedcytokinesactivateActivecytotoxicT cellsDefend against infected cells, cancercells, and transplanted tissuesActivateGives rise toSecrete antibodies that defend againstpathogens and toxins in extracellular fluidPlasmacellsMemoryB cellsB cellsIntact
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