教程医学免疫学apc and ag presentation

1、Wei ChenInstitute of Immunology, ZJU IMMUNOLOGYAntigen-Presenting Cells and Antigen Presentationchapter Introduction Antigen-presenting cellsAntigen processing and presentationContents Introduction Antigen-presenting cellsAntigen processing and presentationContentsA variety of cell types which can t

2、ake up, process antigen and carry antigen in a form (antigenic peptide-MHC molecule complex) that can stimulate lymphocytes. It is also known as accessory cell (A cell).I. Antigen-presenting cell, APCProfessional APCs Dendritic cells, macrophages and B cells, which can express MHC class II molecules

3、.Non-professional APC Endothelial cell (EC) Fibroblastic cell Activated T cellUnder some circumstances, they can express MHC II and present AntigenTarget cells (such as tumor cell, virus infected cells) express MHC I and present endogenous Ag to CD8+ T cells.APC染色彩图Antigen-presenting cellsDendritic

4、cellsMacrophagesB cells几类主要APC的分布及其主要特性 Introduction Antigen-presenting cellsAntigen processing and presentationContentsAntigen 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

5、.Dendritic cells (DC)Antigen-presenting cells1. Surface markersMHC class I/II moleculesCD1a, CD11c, CD83 (human)33D1, NLDC145 (mouse)Co-stimulatory molecules: B7.1(CD80)/B7.2(CD86), CD40, CD44, CD54 LGM-CSFTNF-aIL-42. Sources of DCHSCMyeloid progenitorLymphoid progenitorMyeloid DC MomacrophageMyeloi

6、d DC PMNLymphoid DC3. Classification of DCConventional dendritic cell (cDC) or Myeloid DCs (mDC): secrete IL-12 and be a major stimulator of T cells.Plasmacytoid dendritic cell (pDC) or Lymphoid DCs (LDC): can produce high amounts of IFN-, exert anti-virus effect.Conventional DCsLymphoid tissue DC f

7、ollicular DC (FDC), interdigitating DC (IDC), thymic DCNon-lymphoid tissue DC Langerhans cell, interstitial DCCirculating DC peripheral blood DC, veiled cell1) Interdigitating DC (IDC)Derived from Langerhans cells;FcR- and C3bR-, MHC I and IIhigh;Distribute mainly in the T cell area of secondary lym

8、phoid tissue.Present Ags to T cells Main APC to induce primary immune response.Derived from interstitial DC;MHC -, highly express FcR, C3bR;Locate in lymph follicles which are rich in B cells;Main APC to induce secondary immune response;involved in the generation and maintenance of memory B cells.2)

9、 Follicular DC (FDC)3) Langerhans cells (LC)Immature DCFound in the epidermis (skin) and mucous membranes;MHC I and IIhigh, highly express FcR and C3bR, Birbeck particle (due to langerin expression);Powerful ability to capture and process Ags and migration to lymph node after activation.4. Developme

10、nt of myeloid DC(1) DC precursors Monocytes are the common precursor of macrophage and DC Phenotype: high expression of PRRs (Toll-like recptors, mannose receptor), FcR and CR; low expression of MHC II and co-stimulatory molecule Cellular organlle: MHC calsscompartment, lysosome, Endosome Cytokine:

11、Chemokine and proinflammatory CK such as IL-1, IL-6, IL-15, TNF- secreted by LC Function: Powerful ability to capture and process Ags, but weak ability to stimulate T cells (or weak ability to present Ags); induction of immune tolerance . (2) Immature DC(3) Mature DCPhenotype: low expression of PRRs

12、 (Toll-like recptors, mannose receptor), FcR and CR; high expression of MHC I/II and co-stimulatory molecule (CD54, CD40, CD80, CD86 ); CD1a and CD83+.Function: weak ability to capture and process Ags, powerful ability to present Ags. Dendritic Cell Maturation 5. The function of DC1) Capture and pro

13、cess antigen, participate innate immunityThe expression of receptors related to phagocytosis (FcR, CR, Toll-like receptor, mannose receptor);pDC produce high amounts of IFN-, exert anti-virus effect.5. The function of DC2) DC in immune activation Present antigen and activate T cells The first signal

14、 MHC II-Ag: CD4+ T cells MHC I-Ag: CD8+ T cells The second signal co-stimulating molecules cytokines IL-12 3) Immune regulation secrete CKs and chemokines.4) Induce immune tolerance Central tolerance: induced by negative selection of T cells in the thymus. Peripheral tolerance: immature DC capture a

15、utoantigen when they migrate from non-lymphoid tissue to T cell area of secondary lymphoid tissue, and induce peripheral tolerance. Bone marrow Blood TissueHSCMyeloid progenitorPre-monocyteMonocyteMonocyte Macrophage II. Monocytes and macrophages 1. Differentiation and distributionMHC-I and II molec

16、ules;CAM: LFA-1, ICAM-1, B7, CD40;CKR: M-CSFR;FcR;CR: CR1, CR3, CR4;Pattern-recognition receptor (PRR): mannose receptor, scavenger receptor, Toll-like receptor 2. Surface markers3. Biological functions of M(1) Phagocytosis and cytotoxic activity : chemotaxis : blood-tissue opsonization: Ig, C3b, C4

17、b a number of antimicrobial and cytotoxic substances produced by activated M can destroy phagocytosed microorganisms. Reactive oxygen intermediates, NO, proteinases.(2) Antigen processing and presentation: phagocytosis pinocytosis receptor-mediated endocytosis(3) Secretion of soluble factors to regu

18、late immune response enzymes: lysozyme, myeloperoxidase, etc. cytokines: IL-1, IL-6, TNF, IL-12, IL-18, etc. complement: C1C9, Bf coagulation factor, PG, LTs, ACTH, etc.phagocytosisOpsonizationAg presentationIII. B cellsBCR-mediated phagocytosis enrich antigen when antigen concentration is low.Downl

19、oaded from: StudentConsult (on 1 June 2006 03:50 PM) 2005 Elsevier Mechanisms of Th cell-mediated activation of B cellsB cell-mediated immune responseThe edge of lymphoid follicle Introduction Antigen-presenting cellsAntigen processing and presentationContentsI. Uptake of antigensExogenous antigen E

20、ndogenous antigen 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 extracellular fluidExogenous processing(Streptococcal, Myco

21、bacterial 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 DCphagocytosisMacropinocytosisReceptor-mediated endocytosis2. Uptake of

22、 Ag by macrophagesPhagocytosisPinocytosisReceptor-mediated endocytosis 3. Uptake of Ag by B cellsPinocytosisBCR-mediated endocytosisII. Ag processing and presentation1. The pathway of MHC I-associated endogenous Ag presentation endogenous antigen (such as virus Ag, tumor Ag) antigen peptide（8-13 aa）

23、 Peptide/MHC-I molecule complex to surface of APC submit to CD8+Ttransported to endoplasmic reticulum by TAPdegraded by proteasome (PSMB) in cytoplasmDegradation in the proteasomeThe components of the proteasome include MECL-1, PSMB8, PSMB9.These components are induced by IFN- and replace constituti

24、ve components to confer proteolytic properties.PSMB8 & 9 encoded in the MHCProteasome cleaves proteins after hydrophobic and basic amino acids and releases peptides into the cytoplasmCytoplasmic cellular proteins, including non-self proteinsare degraded continuously by a multicatalytic protease of 2

25、8 subunitsCrystal Structure Of The 20s ProteasomeFrom YeastViewEnd onProteasome, the Cytosolic Meat Grinder That Chops Up ProteinsENDOPLASMIC RETICULUMCYTOSOLPeptide antigens produced in the cytoplasm are physically separated from newly formed MHC class INewly synthesisedMHC class I moleculesPeptide

26、s 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-2PeptideTAP-1TAP-2PeptideTAP-1

27、TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideTAP-1TAP-2PeptideER membraneLumen of ERCytosolTAP-1TAP-2PeptideATP-binding cassette(ABC) domainHydrophobictransmembranedomainPeptide antigensfrom proteasomeEndoplasmic reticulumCalnexin bindsto nascentcl

28、ass I chainuntil 2-M bindsTAP-1TAP-2PeptideTAP-1TAP-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

29、 the floppy MHCCytoplasmic peptides are loaded onto the MHC molecule and the structure es compactMaturation and loading of MHC class IThe formation of peptide-MHC I complexERAP (ER resident aminopeptidase) cleaves antigen peptide into 8-12 amino acid peptides.Erp57 (Hydroxyoxidoreductase) induce the

30、 cleavage and reconstruction ofdisulfide bond in MHC I 2 region, so MHC I molecular be more suitable for antigen peptide binding. Fate of MHC class ISent to lysosomes for degradation Exported to the cell surface2. The pathway of MHC II-associated exogenous Ag presentationExogenous antigen newly synt

31、hesised 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) protease HLA-DMDegrade into 1318aa peptide + releasing the CLIP and allowing other peptide to bind Ag peptide/MHC class II molecule c

32、omplextransport to the surface of APC, recognized by CD4+TPhagocytosis, pinocytosis, FcR-phagocytosisYYPinocytosisPhagocytosisMembrane Igreceptor mediateduptakeYUptake of exogenous antigensComplement receptormediated phagocytosisYFc receptor mediated phagocytosisopsonizationProteases produce 24 amin

33、o acid long peptides from antigensEndosomesExogenous pathwayIncreasein acidityCell surfaceTo lysosomesUptakeProtein antigensIn endosomeCathepsin B, D and L proteases are activated by the decrease in pHPathway for Peptide+MHC-II Formation, from Endocytosis Proteins into Vesicles to Formation of Pepti

34、des on MHC-IINeed 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 maturation and invariant

35、 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 invariant chain peptide

36、(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 with a peptide antigen usi

37、ng 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 peptide-MHC complexes for s

38、urface 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 OccursLoading of MHC-II With Peptides From the Exteri

39、or3. Cross-presentationClass I MHC molecules present exogenous Ags to CD8+ T cellsCross-presentation of Ags by DC plays an important role in anti-viral infection and anti-tumor immunity.Cross-presentation:Do classical MHC class I and class II Presentation explain antigen presentation fully?Problem 1

40、: 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 cells can use intracellular peptides produced in other cel

41、ls 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 transfer antigens into the cytosol.Problem 3: Vaccine antigens are extracellular and yet r