Chapter 8 The Major Histocomptibility Complex (MHC) and Ag Presentation Chapter 9

1. Chapter 8 The Major Histocomptibility Complex (MHC) and Ag Presentation Chapter 9 T-cell Receptor Chapter 10 T-cell Maturation, Activation, and Differentiation

2. Chapter 8 The Major Histocomptibility Complex (MHC) and Ag Presentation Nov 21, 2006

3. 你需要瞭解的課題： • MHC 是如何發現的？ • MHC 的生理功能是什麼？ • MHC 包含哪些基因及分子？ • MHC polymorphism 有什麼生物意義？ • Self-MHC restriction of T cells 是什麼意思？ • 抗原是如何被呈現 (presented) 到 MHC 分子上的？ • 與 MHC 結合的胜肽有什麼性質？

4. TCR and MHC-peptide • TCR (on a T cell) •  peptide (embedded in an • MHC molecule) • MHC (on an Ag-presenting cell or on a virus- infected cell)

5. Gorer (1930s): 1. Rejection of foreign tissue is the result of an immune response to cell-surface molecules. 2. Identification of I, II, III and IV blood-cell Ags and genes in mice. Gorer and Snell (1940s & 1950s): 1. Antigens encoded by the genes in the group II took part in the rejection of transplanted tumors and other tissues. 2. Snell called these genes“histocompatibility (組織相容) genes” (orH-2 genes) 3. Snell was awarded the Nobel Prize in 1980.

6. Human MHC:humanleukocyteantigen(HLA) - the major reason for transplantation rejection Mouse MHC: H-2

7. The MHC Encodes 3 Major Classes of Molecules • Class I MHC: • Expressed on the surface ofnearly all nucleated cells; the major • function of the class I gene products is presentation of peptide Ags • toCD8+T cells. • Class II MHC: • Expressed primarily onAg-presenting cells(macrophages, dendritic • cells, and B cells), where they present processed antigenic peptides • toCD4+T cells • Class III MHC: - no function in Ag presentation • - Generally encode varioussecreted proteinsthat have immune • functions, including components of thecomplementsystem and • molecules involved ininflammation, e.g., C2, C4, factor B, • 21-hydroxylase enzymes, TNFα, TNFβ, heat shock proteins (HSP)

8. D as class I D as class II

9. The MHC loci are highly polymorphic - many alternative • forms of the gene, oralleles, exist at each locus among • the population. • The MHC genes lie close together - the recombination • frequency within the H-2 complex is only 0.5%. • Thus, most individuals inherit the closely linked MHC • genes as two sets, one from each parent. Each set of genes • is referred to as ahaplotype. • The MHC genes arecodominantly expressed; that is, • both maternal and paternal gene products are expressed • in the same cells.

10. (H-2k)

11. Inheritance of MHC Haplotypes inbred homozygous

12. Acceptance or Rejection of Skin Grafts is Controlled by the MHC Type of the Inbred Mice

13. Inheritance of HLA Haplotype in a Hypothetical Human Family outbred heterzygous

14. Congenic MHC Mouse Strain - Inbred mouse strains aresyngeneic or identical at all genetic loci. - Two strains arecongenicif they are genetically identical except at a single locus or region. - Congenic strains can be produced by a series of crosses, backcrosses, and selections.

15. Production of Congenic Mouse Strain Strain A.B Genetically identical to strain A except for the MHC locus or loci contributed by strain B. if a/a = C57BL/10 (B10) b/b = A A.B = B10.A

16. Examples of Recombinant Congenic Mouse Strains

17. MHC Molecules and Genes

18. Class I and Class II Molecules 45kDa 28 kDa 33 kDa 12 kDa Both class I and II molecules are glycoproteins.

19. Organization of Class I MHC Genes b2M gene

20. Organization of Class II MHC Genes = IAb IAb IAa = IAa

21. 3-D Structure of the External Domains of a Human Class I HLA Molecule

22. peptide-binding cleft of MHC class I molecule: - 25Å x 10Å x 11Å - can bind a peptide of 8-10 a.a.

23. Superimposition of the peptide-binding cleft of class I and class II MHC molecules red: HLA-A2 (Class I)blue: HLA-DR1 (Class II)

24. Peptide Binding by MHC Molecules • Several hundred different allelic variants of class • I and II MHC molecules have been identified in • humans. • Peptide binding by class I and class II molecules • does notexhibit thefine specificitycharacteristic • of Ag binding by Ab and TCR. • A given MHC molecule can bindnumerous • different peptides, and some peptides can bind to • several different MHC molecules.

25. Binding Affinity of MHC to Peptides • The association of peptide-MHC molecule is • verystableunder physiological conditions. • - The Kd values range from ~10-6 to 10-10. • - Most of the MHC molecules expressed on the • membrane of a cell are associated with a peptide • of self or nonself origin.

26. Peptide-binding Cleft IsBlocked at Both Ends in Class I Molecules β2M HLA-A2 with HIV RT 309-317 a.a. MHC class I molecules bind to 8 ~ 10 a.a., most commonly9.

27. Anchor Residuesin Nonameric (9) Peptides Eluted from Two Class I MHC Molecules carboxyl-terminal anchor amino-terminal anchor: 2nd or 2nd & 3rd positions Anchor residues tend to be hydro-phobic a.a. In general, any peptide of correct length that contains the same or similar anchor residues can bind to the same class I MHC molecules.

28. Conformational Difference in Bound Peptides of Different Lengths class I

29. An Influenza Virus Peptide and an Endogenous Peptide Bound to a Class I MHC Molecule influenza virus endogenous

30. 13 – 18 amino acid residues Peptide-binding Cleft isOpen at Both Ends in Class II Molecules HLA-DR1 DRα Influenza virus hemagglutinin 306-318 a.a. DRβ MHC class II molecules can bind to 13 ~ 18 a. a. A central core of 13 a.a. determines the ability of a peptide to bind class II.

31. Interacting T cells presented to CD8+ T cells presented to CD4+ T cells Source of peptides endogenous exogenous Ag processing pathway cytosolic pathway endocytic pathway

32. Polymorphism of class I and class II molecules - The diversity of the MHC within a speciesstems from polymorphism, the presence of multiple allelesat a given genetic locuswithin the species. - The MHC possesses anextraordinarily largenumber of different alleles at each locus and is one of themost polymorphicgenetic complexes known in higher vertebrates. HLA-A : 370 alleles, HLA-B : 660 alleles, HLA-C : 190 alleles - The theoretical diversity possible for humans : class I : 370 (A) x 660 (B) x 190 (C) = 4.6 x 107 class II : ~ 8 x 1011 Total : 4.6 x 107 x 8 x 1011 ~ 4 x 1019

33. 實際上你認為人類的 MHC polymorphism 比 4 x 1019多？還是比 4 x 1019少？

34. Antibody diversity MHC polymorphism

35. Variability in the amino acid sequence of allelic class I MHC molecules

36. Location of Polymorphic Amino Acid Residues Most of the residues with significantpolymorphism are located in the peptide-binding cleft

37. Genomic Map of MHC Genes

38. Mouse H-2 is on the chromosome 17 Class I Nonclassical Class IIClass IIIClass I Nonclassical

39. Human HLA is on the chromosome 6 class IInonclassicalclass IIclass IIIclass I nonclassical

40. Cellular Expression of MHC Molecules

41. Cellular Distribution of MHC Class I Molecules - In general, the classical MHC class I molecules are expressed on most nucleated cells. - The highest level of class I molecules are expressed on lymphocytes: 1 % of the total plasma membrane proteins or 5 x 105 molecules / cell. - Fibroblasts, muscle cells, hepatocytes and neural cells express very low levels of class I molecules. - A few cell types (e.g., neurons and sperm cells at certain stages of differentiation) appear to lack class I MHC molecules altogether.

42. Cellular distribution of MHC class II molecules - Class II molecules are expressed constitutively only by Ag-presenting cells (APC), e.g., macrophages, mature dendritic cells, and B cells. - Thymic epithelial cells and some other cell types can be induced to express class II molecules and to function as APC under certain conditions and under cytokine stimilation. - In some cases, class II expression depends on the cell’s differentiation stage.

43. Various MHC Molecules Expressed on APC of a Heterozygous H-2k/d Mouse

44. Nonclassical MHC Class I and Class II Molecules - Structurally similar to class I or class II molecules - Less polymorphic - Expressed at lower level - Tissue distribution is more limited - Functions are being studied

45. Function of HLA-G (nonclassical class I) The expression of HLA-G molecules on cytotrophoblasts(滋養層細胞) at the fetal- maternal interface has been implicated in protection of the fetus from being recognized as foreign and from being rejected by maternal TC cells. Hunt, J.S., M.G. Petroff, R.H. McIntire & C. Ober. HLA-G and immune tolerance in pregnancy. FASEB J 19: 681-693, 2005

46. CTB: cytotrophoblast cell

47. Regulation of MHC Expression • - Defect in class II MHC transcriptional activator CIITA or • RFX cause one form of bare lymphoyte syndrome (BLS). • The expression of MHC molecules is regulated by various • cytokines, e.g., interferons (α, β,γ) and tumor necrosis • factors (TNF), etc. • MHC expression on cell surfaces is decreased by infection • with certain viruses, including human cytomegalovirus • (CMV), hepatitis B virus (HBV), adenovirus 12 (Ad12), etc. • Decreased expression of class I MHC molecules is likely to • help viruses evade the immune response by reducing the • presentation of viral peptide on virus-infected cells.

48. MHC and Immune Responsiveness

49. Important Roles of MHC in the Immune Response 1. MHC molecules act asantigen-presenting structure. 2. MHC molecules expressed by an individual influence the repertoire of antigensto which that individual’s TH cells and TC cells can respond. 3. MHC partly determines theresponseof an individual to antigens of infectious organisms. 4. MHC has been implicated in the susceptibility todisease and in the development ofautoimmunity.

50. Self-MHC Restriction of CD4+ T Cells APC T cells measure the 2nd response against immunized Ag Class II MHC Restriction