1. Major Histocompatibility Complex and Antigen Presentation 미생물학교실 권 형 주

2. Antigen Presentation, MHC-Peptide complex, TCR Medzhitov R, & Janeway C Jr., N. Engl. J. Med., 2000. 343, 338-344

3. MHC 의 발견 - Polymorphic: many alternative forms of the gene, or allele, exist at each locus among the population - Inbred mice: Homozygous at every genetic locus : Every mouse of an inbred strain is genetically completely identical (syngenic) - Congenic mouse strains: a single genetic region is responsible for most rejection phenomena

4. Simplified organization of the MHC in the mouse and human

7. Major Histocompatibility Complex (MHC) molecules - T 세포에 항원을 전달 Recognition by the  TCR requires antigen to be bound to an MHC molecule : Short peptide fragments (endogeneously synthesized)-MHC class I complex : short peptide fragments (extracellular origin)-MHC class II complex : Peptide-MHC complexes serve as ligands for TCRs

8. MHC molecule provide a sophisticated surveillance system for intracellular antigens : MHC class I molecules - intrinsic antigens 인식 - antigenic peptides from viruses or other pathogens that inhabit the cell - present antigen to cytotoxic T cells (CD8 + T cells) - controlling viral infections by lysing infected cells : MHC class II molecules – extrinsic antigens 인식 - present antigen to helper T cells (CD4 + T cells) - aid B cells in generating antibody responses to extracellular protein antigens : antigenic peptides are produced by proteolytic processing of proteins - Antigen processing and presentation

9. MHC class I and II molecules

10. MHC class I - Glycosylated heavy chain (  -chain, 45 kDa) associated with  2 -microglobulin (12 kDa) - Heavy chain : three extracellular domains (  1,  2,  3 ) : transmembrane domain : cytoplasmic tail : intracellular disulfide bond:  2,  3 :  3 domain-homologous Ig C domain interacts with CD8 Tc cells

11.  2 -microglobulin is essential for expression of MHC class I molecules - non-polymorphic in humans - Ig constant region domain - associate with class I-like molecules (CD1, Fc receptor) - The cell surface-mutant mice lacking  2 m do not express class I  : essential for the expression of all class I molecules  - Daudi cells (tumor) : absence of  2 m, MHC class I  chain –not in membrane  : transfection of  2 m –MHC class I appear on membrane

12. MHC class II - Heterodimers: heavy  chains: 30-34 kDa light  chains: 26-29 kDa - Extracellular domains :  1 and  2,  1 and  2 - Peptidie-binding cleft :  1 -  1 - Transmembrane region : ~30 residues - Cytoplasmic domain : 10-15 residues -  2 and  2 domains  class I  3 and  2 m -  1,  2,  1 domains: N-glycosylated -  2 domain : binding site for CD4 Blue : HLA-DR1 Red : HLA-A2

13. The exon/intron arrangement of class I and II genes reflects their domain structure

14. Class I and II molecules exhibit polymorphism in the region that binds to peptides

15. - The bound peptides isolated from cell surface MHC molecules  purify and sequence the peptides (HPLC) : foreign peptides – internalized antigens or viral particles : self molecules produced within the cell or endocytosed from extracellular fluids Class I MHC-peptide interaction Example of anchor residues (blue) in nonameric peptides eluted from two class I MHC molecules

17. Class II MHC-peptide interaction - Incorporates a number of binding pockets, though the locations are somewhat different from that on class I molecules - Class II Is not closed at the ends, so bound peptides extend out of the ends of the groove - 13-18 amino acids Peptides binding MHC class II are less uniform in size than those binding MHC class I molecules - MHC class II : extend beyond the ends of the cleft =  antigen processing pathway (chapter 7)

18. Class I and Class II molecules exhibit diversity within a species, and multiple forms occur in an individual - Ab, TCR diversity : somatic process : gene rearrangement, somatic mutation -MHC : polymorphism : multiple alleles at a given genetic locus within the species : polygenic (HLA-A, -B, and –C) : HLA-A, -B, and –C : 370X660X190, : 46 million different class I haplotypes possible in the population Linkage disequilibrium : the actual diversity is known to be less, because certain allelic combinations occur more frequently in HLA haplotype than predicted by random combination : Successful organ transplants ????

19. Functional relevance of MHC polymorphism

21. Detailed genomic Map of MHC genes

22. Cellular expression of MHC Molecules - Class I MHC molecules : Expressed on most nucleated cells : Lymphocytes – 5 x 10 5 molecules/cell : Cell 에 따라 발현정도 다름 - Class II MHC molecules : APC, macrophages, mature dendritic cells, thymic epithelial cells…… : Cytokine stimulation, differentiation stage 에 따라 다름 ……

23. Human class II genes are located in the HLA-D region - HLA-D region, Three loci : DR, DQ, DP - DR family: single a gene (DRA) up to nine b genes (DRB1-9)including pseudogenes - The class II region also contains genes that encode proteins involved in antigen presentation that are not expressed at the cell surface

24. - The organization and length of the DRB region varies in different haplotypes, with different numbers of  chain expressed MHC polymorphism is concentrated in and around the peptide-binding cleft - Extreme degree of polymorphism (structural variability) - Class I :  1 and  2 domains - Class II : DR , DQ , DQ  chains, DP   less polymorphic --  peptide binding site DR  chains are invariant - Individuals have two MHC haplotypes

25. Regulation of MHC Expression TRAF6 p65 c-Rel IBIB HLA-DRA XX2Y RFX CIITA BB MyD88 CpG-DNA LPS NF-  B IRAK TLRs NF-Y IRF-1 CIITA Stat1 JAK1, 2 IFN-  USF-1 P Stat1 p38 MEK-1 ? - Regulation MHC class II expression - CIITA : class II transcriptional activator

26. - Regulation MHC class I expression

27. MHC and Diseases Susceptibility An individual’s MHC haplotype affects their susceptibility to disease Different MHC molecules affect: - The ability to make immune responses, including the level of antibody production - Resistance or susceptibility to infectious disease - Resistance or susceptibility to autoimmune diseases and allergies Why the MHC is so polymorphic? - many different pathogens  selective advantage in having different MHC molecules - select for different MHC molecules in each area

28. Self-MHC Restriction of T cells CD4 + and CD8 + T cells can recognize antigen only when presented by a self-MHC molecule - CD4 + T H cell is class II MHC restricted - CD8 + Tc cells is class I MHC restricted

29. Role of Antigen-Presenting cells Processing of antigen is required for recognition by T cells

30. Most cells can present antigen with class I MHC; presentation with class II MHC is restricyed to PACs - Display peptides associated with class II MHC to CD4 + T H cell : Antigen-presenting cells - Display peptides associated with class I MHC to CD8 + Tc cells : Target cells - Professional antigen-presenting cells : constitutively ecpress class II MHC, costimulatory molecules - Nonprofessional antigen-presenting cells

31. Evidence for different antigen-processing and presentation pathways Overview of cytosolic and endocytic pathways for processing antigen

32. - Inhibitor of protein synthesis : emetine : Class I presentation inhibition - Endocytic processing blocker : chloroquine : Class II presentation inhibition

33. Endogenous antigens : The Cytosolic Pathway Cytosolic proteolytic system for degradation of intracellular proteins - Immunoproteasome : induced by IFN- , TNF- , virus-infected cells

34. TAP (transporter associated with antigen processing)

35. Assembly and stabilization of class I MHC molecules Molecular chaperones : calnexin, calreticulin, tapasin

36. Exogenous antigens : The Endocytic Pathway

37. - Ii (CD74) : invariant chain - CLIP : class II-associated invariant chain peptide -HLA-DM : catalyze the exchange of CLIP with antigenic peptide - HLA-DO : negative regulator of class II antigen processing by binding to HLA-DM and inhibiting its role in the dissociation of CLIP from class II MHC molecule (b) HLA class II-peptide or CLIP

39. Cross-Presentation of Exogenous Antigens

40. - CD1 molecules : structurally related to MHC class I non-polymorphic - Group I : CD1a, CD1b, and CD1c - Group II : CD1d - Identified on cortical thymocytes: T-cell differentiation marker - Found on B cells and dendritic cells Presentation of Nonpeptide Antigens

41. Antigen presentation by CD1 - CD1 molecules : structurally related to MHC class I non-polymorphic - Group I : CD1a, CD1b, and CD1c - Group II : CD1d - Identified on cortical thymocytes: T-cell differentiation marker - Found on B cells and dendritic cells

42. CD1 is an MHC class I-like molecule which presents lipid antigens - CD1d 의 구조분석 : X-ray crystallography : deep electrostatically neutral antigen-binding groove : hydrophobic acyl groups of the lipids into the large hydrophobic pockets : polar groups (phosphate, carbohydrate) interact with the TCR : lipid antigen-specific T cells : NK-T cells : acidic endosomal compartments  lipid antigens: partially unfolded at low pH -Group CD1 : present lipids from mycobacteria and Haemophilus influenzae  stimulate CD4+, CD8+ T cells  role in antimicrobial defense - CD1d : present lipids from parasites such as Plasmodium falciparum and Trypanosoma brucei