MHC and AG Presentation1 MHC and Antigen Presentation Chapters 6 & 7 Self-Test Questions: Chap 6 A: 1 – 5, 8 Note: for A-5 know MHC I - III B – D: all Chap 7 A: all B1: 1, 4 – 8, 11, 12 B2-4: all C1: 1,3 C2-4: all D: all E: 1, 3

MHC and AG Presentation2 What is the structure of MHC-I proteins? MHC-I α chain Β-microglobulin Binding cleft Closed ends Anchor residues Peptide may bend Expressed in all nucleated cells

MHC and AG Presentation3 What is the structure of MHC-II proteins? MHC-II α and β chains Binding cleft open ends Anchor residues Peptide lies flat Expressed only in pAPC MHC 3D Models

MHC and AG Presentation4 MHC proteins bind to peptides based upon general properties each MHC protein can bind to many different peptides Shared properties of peptides binding to two different MHC-II Shared properties of peptides binding to a MHC-I From Grey et al., Sci Amer November, 1989

MHC and AG Presentation5 How are MHC genes arranged on Chromosome 6? MHC is polygenic Confusing terminology! HLA complex in humans H-2 complex in mice Class II loci DP, DQ and DR α and β peptide genes Class I loci A, B, C 1 gene each (β-microglobin gene is elsewhere) Class III loci misc other genes Also, non-classic MHC-I and -II genes e.g., DM, DO

MHC and AG Presentation6 (Single gene for DR α peptide) Further polygenicity of MHC genes There are multiple copies of some A and B genes! e.g., DRB1, DRB3, … DRB9 DPA1, DPA2 and DPB1, DPB2 DQA1, DQA2 and DQB1, DQB2, DQB3 -- many pseudogenes also (e.g DRB2) DR locus yields different MHC-II proteins (Multiple genes for DR β peptide ) γ gene DRβ1/DRαDRβ3/DRαDRβ4/DRα

MHC and AG Presentation7 MHC genes are also “Polymorphic” Different people may possess slightly different alleles for MHC peptides! *01 *02 *03 *04 *05 … *16 *01 *02 *03 *01 *02 *03 γ gene Broad allele classes DR53 = HLA “serotypes” -- MHC proteins with distinct antigenic properties DR3 DR4 DR5 … DR DR52 All yield

MHC and AG Presentation8 “DRβ” = name of MHC peptide subunit “DR3” = HLA serotype family -- occurs in many different polymorphic forms… At the DNA level “DRB1” = a locus of gene “DRB1*03” = broad allele type “DRB1*0301” = minor allele type *01 *02 *03 *04 *05 … *16 Minor alleles also exist within broad allele Alleles are further polymorphic *0101 *0102 *0103 … *0122 *0301 *0302 *0303 … *0341 MHC-II DRβ Loci Are all forms of HLA… DR3 DR1

MHC and AG Presentation9 How polymorphic is HLA? Polygenetism is good Polymorphism is good for the individual. Why?for the species. Why? Good explanation Class II alleles Class I allelesGood explanationClass II allelesClass I alleles

MHC and AG Presentation10 MHC genes/serotypes are inherited as a set (haplotype) 1 from mother, one from father Crossing-over can create new haplotypes

MHC and AG Presentation11 Different HLAs predispose individuals toward disorders Fraction of afflicted population with HLA Ag Fraction of normal population with HLA Ag RR=

MHC and AG Presentation12 How many forms of HLA exist on cells? Genes display ‘codominance’ -- up to 6 forms of MHC-I forms of MHC-II Peptides from different chromosomes can combine MHC proteins: ~ 10 5 copies / cell ~10 18 in species

MHC and AG Presentation13 How is HLA tissue typing performed ? -- Determine HLA antigens/genes of recipient and potential donors “HLA antigen typing” -- use lymphocytes -- serological (antibody) testing -- genetic testing (e.g., PCR) “Mixed Lymphocyte Culture” -- culture together donor and recipient lymphocytes -- look for immunological response from recipient cells HLA polymorphism (HLA serotype variation) is the primary cause of organ transplant rejection

MHC and AG Presentation14 How is the mouse H-2 complex organized? MHC-I at K, D and L -- K & D (& L sometimes) MHC-II at A and E loci -- IA & IE I II II I (I) I I I II II II Mice can be bred: -- Syngeneic e.g. H-2 k, H-2 d -- both chromosomes have same haplotype -- Congeneic C3H x BALB/C -  H-2 d/k Mouse Strain Haplotype H-2 alleles MHC-I _ MHC-II_ MHC-I K IA IE D C3H kkkkk BALB/c ddddd C57BL/6 bbb b b A akkkd B10.A (3R) i3bbdd

MHC and AG Presentation15 How does MHC haplotype in influence recognition of antigens by TCRs? From H-2 k mice the genes for a T H -cell TCR against a hen-egg lysozyme (HEL) peptide were transferred to H-2 d, H-2 k and H-2 d/k mice. The mice were also transfected with the HEL gene, which is expressed only in the periphery (not thymus). A. HEL peptides will presented on which cells and on which MHC type? B. In mice of which haplotype(s) would the HEL T-cells be released from the thymus? C. In mice of which haplotype(s) would the HEL T-cells bind to the HEL peptides? D. Why was HEL-expressing virus used, instead of injecting HEL directly?

MHC and AG Presentation16 Antigen Presentation -- chapter 7 How are peptides loaded into MHC-II? Exogenous antigens Prof APCs Endolysosome Invariant chain ( I i) & CLIP HLA-DM

MHC and AG Presentation17 How are peptides loaded into MHC-I? Endogenous antigens All nucleated cells Protein synthesis Ubiquitin & Proteasomes -- special immuno-proteosomes TAP transporters Chaperone proteins

MHC and AG Presentation18 Antigen “Cross presentation” Exogenous AG on MHC-I Possibly only certain DCs Why is this necessary? strongest evidence for 2.

MHC and AG Presentation19 Other mechanisms of antigen presentation CD1 family (a-d) -- non-peptide antigens -- e.g., lipopeptides, glycolipids & phospholipids Some T-cells are CD1-restricted