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1、IMMUNOLOGYAntigen-Presenting Cells and Antigen PresentationchapterOutline:WhatareAPCandprofessionalAPC?DescribeMHCclassIandMHCclassIIpresentationpathways.WhatarethephysiologicalsignificancesforthesetwopathwayThedifferencebetweenimmatureDendriticCellandmatureDC.WhatisCrosspresentation?Whatthefunction
2、ofCD1molecule? Introduction Antigen-presenting cellsAntigen processing and presentation MHC I-associated endogenous Ag presentation pathway MHC II-associated exogenous Ag presentation pathway Cross presentation CD1 presentation pathwayContents Introduction Antigen-presenting cellsAntigen processing
3、and presentation MHC I-associated endogenous Ag presentation pathway MHC II-associated exogenous Ag presentation pathway Cross presentation CD1 presentation pathwayContentsA variety of cell types which can take up, process antigen and carry antigen in a form (antigenic peptide-MHC molecule complex)
4、that can stimulate lymphocytes. Dendritic cells, monocytes/macrophages and B cells are professional APCs.Antigen-presenting cell, APCThe category of APCCellsthatexpressMHCclassI,presentendogenousantigenArekilledbyCD8+cellsArecalledTarget cellsCellsthatexpressMHCclassII,presentexogenousantigenActivat
5、etheCD4+TcellresponseArecalledAntigen presenting cells Professional APCs Dendriticcells,macrophagesandBcells,whichcanexpressMHCclassIImolecules.Non-professional APCEndothelialcell(EC)FibroblasticcellActivatedTcellUndersomecircumstances,theycanexpressMHCIIandpresentAntigenAntigen presenting cellsAPC染
6、色彩图Antigen-presenting cellsDendritic cellsMacrophagesB cellsThe characteristics of APCsAntigen presentation The process by which certain cells in the body (APC) express antigen peptide-MHC molecule complex on their cell surface in a form recognizable by T lymphocytes.Antigen-presenting cells树突状细胞（树突
7、状细胞（Dendritic cell, DC）1. Surface markersMHCclassI/IImoleculesCD1a,CD11c,CD83(human)33D1,NLDC145(mouse)Co-stimulatorymolecules:B7.1(CD80)/B7.2(CD86),CD40,CD44,CD54I.Dendritic cells (DC)GM-CSFTNF-IL-42. Sources of DCHSCMyeloid progenitorLymphoid progenitorMyeloid DC MomacrophageMyeloidDCPMNLymphoid D
8、C3. Classification of DCConventionaldendriticcell(cDC)orMyeloidDCs(mDC):secreteIL-12andbeamajorstimulatorofTcells.Plasmacytoiddendriticcell(pDC)orLymphoidDCs(LDC):canproducehighamountsofIFN-,exertanti-viruseffect.Conventional DCsLymphoidtissueDCfollicularDC(FDC),interdigitatingDC(IDC),thymicDCNon-ly
9、mphoidtissueDCLangerhanscell,interstitialDCCirculatingDCperipheralbloodDC,veiledcell1) Interdigitating DC (IDC)DerivedfromLangerhanscells;FcR-andC3bR-,MHCIandIIhigh;DistributemainlyintheTcellareaofsecondarylymphoidtissue.PresentAgstoTcellsMain APC to induce primary immune response.Interdigitating DC
10、( IDC Interdigitating DC( IDC ）Express high level of class, MHC molecules and B7，lack of FcR and CR, can stimulate T cells.MainAPCtoinducesecondaryimmuneresponse;DerivedfrominterstitialDC;MHC-,highlyexpressFcR,C3bR;LocateinlymphfollicleswhicharerichinBcells;involvedinthegenerationandmaintenanceofmem
11、oryBcells.2) Follicular DC (FDC)BcellsFDC3) Langerhans cells (LC)ImmatureDCFoundintheepidermis(skin)andmucousmembranes;MHCIandIIhigh,highlyexpressFcRandC3bR,Birbeckparticle(duetolangerinexpression);PowerfulabilitytocaptureandprocessAgsandmigrationtolymphnodeafteractivation.4. Development of myeloid
12、DC(1) DC precursors Monocytes are the common precursor of macrophage and DCPhenotype:highexpressionofPRRs(Toll-likerecptors,mannosereceptor),FcRandCR;lowexpressionofMHCIIandco-stimulatorymoleculeCellularorganlle:MHCcalsscompartment,lysosome,EndosomeCytokine:ChemokineandproinflammatoryCKsuchasIL-1,IL
13、-6,IL-12,TNF-secretedbyLCFunction:PowerfulabilitytocaptureandprocessAgs,butweakabilitytostimulateTcells(orweakabilitytopresentAgs);inductionofimmunetolerance. (2) Immature DC(3) Mature DCPhenotype:lowexpressionofPRRs(Toll-likerecptors,mannosereceptor),FcRandCR;highexpressionofMHCI/IIandco-stimulator
14、ymolecule(CD54/ICAM-1,CD40,CD80,CD86);CD1aandCD83+.Function:weakabilitytocaptureandprocessAgs,powerfulabilitytopresentAgs.Difference between iDC and mDC5. The function of DC1) Capture and process antigen, participate innate immunityTheexpressionofreceptorsrelatedtophagocytosis(FcR,CR,Toll-likerecept
15、or,mannosereceptor);pDCproducehighamountsofIFN-,exertanti-viruseffect.5. The function of DC2) DC in immune activation Present antigen and activate T cellsThefirstsignalMHCII-Ag:CD4+TcellsMHCI-Ag:CD8+TcellsThesecondsignalco-stimulatingmoleculescytokines:IL-12 3) Immune regulation secreteCKsandchemoki
16、nes.4) Induce immune tolerancenCentraltolerance:inducedbynegativeselectionofTcellsinthethymus.nPeripheraltolerance:immatureDCcaptureautoantigenwhentheymigratefromnon-lymphoidtissuetoTcellareaofsecondarylymphoidtissue,andinduceperipheraltolerance.TheNobelPrizeinPhysiologyorMedicine2011Ralph M. Steinm
17、anDendritic cells, DCR.M.SteinmanandZ.A.Cohn.J. Exp. Med. 137, 11421162;1973 How T cell find the right dendritic cellNature. 2004 427(6970):154-9Nature. 2004 427(6970):154-9 Short T cell-DC contacts during phase IShort T cell-DC contacts during phase IT cell(green)T cell(green)Antigen-loaded DC(red)
18、Antigen-loaded DC(red)Stable Tcell-DC interaction during phase IIT cell(green)T cell(green)Antigen-loaded DC(red)Antigen-loaded DC(red)Antigen dose governs interactive behavior with dendritic cells and sets a threshold for T cell activationNat Immunol. 2008 ;9(3Nat Immunol. 2008 ;9(3): ):282-91282-9
19、1P14 T cell(green)P14 T cell(green)C-peptide-loaded C-peptide-loaded DC(red)DC(red)OT-1 (blue)OT-1 (blue) Bone marrow Blood TissueHSCMyeloid progenitorPre-monocyteMonocyteMonocyte Macrophage II. Monocytes and macrophages 1. Differentiation and distributionDifferentnamesindifferenttissuesMonocyte(blo
20、od)Kupffercells(liver)Mesangialcells(kidneyglomerulus)Microglia(brain)Alveolarmacrophages(lung)Histiocyte(connectivetissue)nMHC-IandIImolecules;nCAM:LFA-1,ICAM-1,B7,CD40;nCKR:M-CSFR;nFcR;nCR:CR1,CR3,CR4;nPattern-recognitionreceptor(PRR):mannosereceptor,scavengerreceptor,Toll-likereceptor2. Surface m
21、arkersrested Mresponsive Mstimulated Mactivated Msuppressor M病原体signalLFA-1MHC-II细胞增生趋化，杀菌提呈Ag，激活LC，结合TC，过度活化适度活化PGE抑制免疫功能杀瘤，杀菌First signal:MAF/IFN-,MSFsecond signal:LPS/IFN-,MSF,CK,123TheprocessofMactivation3. Biological functions of M (1) Phagocytosis and cytotoxic activity : anumberofantimicrobia
22、landcytotoxicsubstancesproducedbyactivatedMcandestroyphagocytosedmicroorganisms.Reactiveoxygenintermediates,NO,proteinases.(2) Antigen processing and presentationphagocytosisOpsonization(3) Secretion of soluble factors to regulate immune response enzymes:lysozyme,myeloperoxidase,etc.cytokines:IL-1,I
23、L-6,TNF,IL-12,IL-18,plement:C1C9,Bfcoagulationfactor,PG,LTs,ACTH,etc.(4)Immune regulation: Up-regulation: Ag-presentation; secretion of cytokines that up-regulate immune response,e.g.IL-12,IL-18 Down-regulation: inhibitory M produce IL-10, TGF- , PG, etc.III. B cellsBCR-mediatedphagocytosisenrichant
24、igenwhenantigenconcentrationislow.MarkersofBcellsDownloaded from: StudentConsult (on 1 June 2006 03:50 PM) 2005 Elsevier Mechanisms of Th cell-mediated activation of B cellsB cell-mediated immune responseTheedgeoflymphoidfollicle Introduction Antigen-presenting cellsAntigen processing and presentati
25、onContentsAntigen presentation The process by which certain cells in the body (APC) express antigen peptide-MHC molecule complex on their cell surface in a form recognizable by T lymphocytes.I. Uptake of antigensexogenous antigensBacteria,cellsandsolubleproteinsprocessedbyAPCendogenous antigensProdu
26、cedwithinthecells,Suchasviralproteinsortumorproteinsprocessedbyhostcell YThe site of pathogen replication or mechanism of antigen uptake determines the antigen processing pathway usedYCytosolic compartmentEndogenous processing(Viral antigens, tumor antigens)Vesicular CompartmentContiguous with extra
27、cellular fluidExogenous processing(Streptococcal, Mycobacterial antigens)Distinct mechanisms of antigen generation are used to raiseT cells suited to the elimination of endogenous or exogenous pathogensINTRACELLULAR REPLICATIONEXTRACELLULAR ORENDOSOMAL REPLICATION1. Uptake of Ag by DCphagocytosisMac
28、ropinocytosisReceptor-mediatedendocytosis2. Uptake of Ag by macrophagesPhagocytosisPinocytosisReceptor-mediatedendocytosis3. Uptake of Ag by B cellsPinocytosisBCR-mediatedendocytosisII. Ag processing and presentationTwoAntigenProcessingPathwaysEndogenousantigensincytosolpresentedonclassIMHCmolecules
29、toCD8+Tcells.ExogenousantigensinendosomespresentedonClassIIMHCmoleculestoCD4+Tcells.1. The pathway of MHC I-associated endogenous Ag presentation endogenous antigen (such as virus Ag, tumor Ag) antigen peptide（8-13 aa） Peptide/MHC-I molecule complex to surface of APC submit to CD8+Ttransported to en
30、doplasmic reticulum by TAPdegraded by proteasome (PSMB) in cytoplasmDegradation in the proteasomeThe components of the proteasome include MECL-1, PSMB8, PSMB9.Structure: 20S 26SFunction: Degradation of proteinCytoplasmic cellular proteins, including non-self proteinsare degraded continuously by a mu
31、lticatalytic protease of 28 subunitsProteasome, the Cytosolic Meat Grinder That Chops Up ProteinsCrystal Structure Of The 20s ProteasomeFrom YeastViewEnd onENDOPLASMIC RETICULUMCYTOSOLPeptide antigens produced in the cytoplasm are physically separated from newly formed MHC class INewly synthesisedMH
32、C class I moleculesPeptides needaccess to the ER inorder to be loaded onto MHC class I moleculesPSMBTAPER membraneLumen of ERCytosolTransporter-associated withantigen processing (TAP1 & 2)Transporter has preference for 8-16 amino acid peptideswith hydrophobic C termini.TAP-1TAP-2PeptideTAP-1TAP-2Pep
33、tideTAP-1TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideER membraneLumen of ERCytosolTAP-1TAP-2PeptideATP-binding cassette(ABC) domainHydrophobictransmembranedomainPeptide antigensfrom proteasomeEndogenous Ag process
34、ing transport to ERPeptidesfromproteolysisbindtoa“transporterproteinassociatedprocessing”(TAP)TAPisaheterodimerwhichusesATPtohelptransportpeptides(8-16aas)tolumenofERUsuallybasicaasCOOHendofpeptidechainEndoplasmic reticulumCalnexin bindsto nascentclass I chainuntil 2-M bindsTAP-1TAP-2PeptideTAP-1TAP
35、-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2Peptide2-M binds and stabilises floppy MHCTapasin, calreticulin, TAP 1 & 2 form a complex with the floppy MHCCytoplasmic peptides are loaded onto
36、 the MHC molecule and the structure becomes compactMaturation and loading of MHC class IcalnexinStructure88kDintegralERmembranechaperoneproteinFunctionBindstoanascentMHCclassI chainafterreleasefromaribosomeintotheERlumensothatthechainwillnotleavetheERuntilitbindsbothashortpeptidesequenceand2microgob
37、ulinERAP(ERresidentaminopeptidase)cleavesantigenpeptideinto8-12aminoacidpeptides.Erp57(Hydroxyoxidoreductase)inducethecleavageandreconstructionofdisulfidebondinMHCI2region,soMHCImolecularbemoresuitableforantigenpeptidebinding.The formation of peptide-MHC I complexFate of MHC class ISent to lysosomes
38、 for degradation Exported to the cell surface2. The pathway of MHC II-associated exogenous Ag presentationExogenous antigen newly synthesised MHC class II molecule (in the endoplasmic reticulum) endosome Ii binds in the groove of MHC class II molecule lysosome protease M II C phagolysosome li (CLIP)
39、 protease HLA-DMDegrade into 13 18aa peptide + releasing the CLIP and allowing other peptide to bind Ag peptide/MHC class II molecule complextransport to the surface of APC, recognized by CD4+TPhagocytosis, pinocytosis, FcR-phagocytosisYYPinocytosisPhagocytosisMembrane Igreceptor mediateduptakeYUpta
40、ke of exogenous antigensComplement receptormediated phagocytosisYFc receptor mediated phagocytosisopsonizationProteases produce 24 amino acid long peptides from antigensEndosomesExogenous pathwayIncreasein acidityCell surfaceTo lysosomesUptakeProtein antigensIn endosomeCathepsin B, D and L proteases
41、 are activated by the decrease in pHNeed to prevent newly synthesised, unfolded self proteins from binding to immature MHC Invariant chain stabilises MHC class II by non-covalently binding to the immature MHC class II molecule and forming a nonomeric complexIn the endoplasmic reticulumMHC class II m
42、aturation and invariant chain involve in the assembling and folding of MHC class II molecule; Block the groove of MHC class II molecule; Lead the assembled class II molecule to M II C.The functions of Ii:CLIP：class II-associated invariant chain peptideEndosomesCell surfaceUptakeClass II-associated i
43、nvariant chain peptide (CLIP)(-Ii)3 complexesdirected towardsendosomes byinvariant chainCathepsin L degrades Invariant chainCLIP blocks groove in MHC moleculeMHC Class IIcontaining vesiclesfuse with antigencontaining vesiclesHLA-DM catalyses the removal of CLIPMIIC compartmentHLA-DMReplaces CLIP wit
44、h a peptide antigen using a catalytic mechanism (i.e. efficient at sub-stoichiometric levels)Discovered using mutant cell lines that failed to present antigenHLA-DO may also play a role in peptide exchangeSequence in cytoplasmic tail retains HLA-DM in endosomesHLA-DMHLA-DRMIIC compartment sorts pept
45、ide-MHC complexes for surface expression orlysosomal degradationSurface expression of MHC class II-peptide complexesExported to the cell surface (t1/2 = 50hr)Sent to lysosomes for degradation MHC-II Goes from Golgi (G) to MHC-II Compartment (MIIC) Where Peptide Loading OccursTwo antigen-processing p
46、athwaysMHC class IMHC class IIMajor antigen sourcesendogenous antigenexogenous antigenProcessing machineryproteasomelysosomal enzymes, MIICCell type where activeall nucleated cellsprofessional APCsSite of antigen-MHC binding endoplasmic reticulum MIICMHC utilizedMHC class IMHC class IIchaperone and
47、transport moleculeCalnexin, TAPIi, CalnexinPresents toCD8+ T cell (Tc)CD4+ T cells (Th)3. Cross-presentationClass MHC molecules also present exogenous antigens to CD8+T cellsClass MHC molecules also present endogenous antigens to CD4+T cellsCross-presentation:Do classical MHC class I and class II Pr
48、esentation explain antigen presentation fully?Problem 1: Classical MHC class I presentation would require DCs to get infected and produce peptides in the DC cytoplasm. However, many viruses do NOT infect dendritic cells and still activate cytotoxic CD8+ T cells.There must be a way that dendritic cel
49、ls can use intracellular peptides produced in other cells to activate cytotoxic T cells.Problem 2: Phagocytosed pathogens such as Salmonella, Brucella, and Leischmania can elicit MHC class I-dependent cytotoxic CD8+ T cell proliferation. To elicit Class I responses, pathogens in phagosomes must tran
50、sfer antigens into the cytosol.Problem 3: Vaccine antigens are extracellular and yet result in cytotoxic CD8+ T cell responses. Extracellular antigens must be capable of transfer into the cytosol to elicit class I responses.Cross-presentation:Typically MHC II antigens are extracellular and MHC I ant
51、igens are cytosolic.However, this is no longer absolutely true - examples that violate both directions exist. Thus, ANY protein can potentially be presented by MHC I or MHC II.Cross presentation = MHC I presentation of exogenous antigens. Sources of antigen for MHC I presentationSources of antigen f
52、or MHC II presentation:TrombettaandMellman,AnnualReviewsofImmunology,23:975,2005CD1 ProteinsClassILikeMHCMoleculesCD1a-earenonpolymorphicClassIlikemoleculesthatassociatewithb2m.CD1a-cpresentalimitednumberofbacterialglycolipidantigenstoTcells,whereasCD1dpresentlipidantigentoNKcells.Bacterialcellwalll
53、ipidsmakeexcellentinnateimmunetargetsbecausetheyarenoteasilymutated.CD1AntigenPresentationCD1proteinshavehydrophobicbindinggrooveforhydrocarbonchainsoflipidtails.HydrophilicsugarendorlipidheadofantigenavailableforTcellbinding.CD1AntigenProcessingJayawardena-WolfandBendelac2001CurrOpinImmunol13:109CD1proteinssamplelipidantigensindifferentcompartments.Lipidandglycolipidantigensstillrequireprocessing.ProcessingofClassIandClassIIvsCD1Antigens
