MHC and Antigen Presentation Chapters 6 & 7

1. 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 Presentation

2. 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 Presentation

3. 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 Presentation

4. 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 Presentation

5. 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 Presentation

6. 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) (Single gene for DRα peptide) (Multiple genes for DRβ peptide) γ gene DR locus yields different MHC-II proteins DRβ1/DRα DRβ3/DRα DRβ4/DRα MHC and AG Presentation

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

8. Alleles are further polymorphic MHC-II DRβ Loci *01 *02 *03 *04 *05 … *16 Minor alleles also exist within broad allele *0301 *0302 *0303 … *0341 *0101 *0102 *0103 … *0122 Are all forms of HLA… DR3 DR1 “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 MHC and AG Presentation

9. How polymorphic is HLA? Polygenetism is good Polymorphism is good for the individual. Why? for the species. Why? Good explanationClass II allelesClass I alleles MHC and AG Presentation

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

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

12. How many forms of HLA exist on cells? Genes display ‘codominance’ -- up to 6 forms of MHC-I -- 12+ forms of MHC-II Peptides from different chromosomes can combine MHC proteins: ~ 105 copies / cell ~1018 in species MHC and AG Presentation

13. HLA polymorphism (HLA serotype variation) is the primary cause of organ transplant rejection 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 MHC and AG Presentation

14. I I I II II II I II II I (I) 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 Mice can be bred: -- Syngeneic e.g. H-2k, H-2d -- both chromosomes have same haplotype -- Congeneic C3H x BALB/C - H-2d/k MHC and AG Presentation

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

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

17. 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 Presentation

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

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