The "minimal essential MHC" revisited: both peptide-binding and cell surface expression level of MHC molecules are polymorphisms selected by pathogens in chickens.
Birds, like mammals, have a highly polymorphic MHC that determines strong allograft rejection. However, in contrast to mammals, there are a number of viral diseases for which resistance and susceptibility are determined by particular chicken MHC haplotypes. We have found that certain common chicken MHC haplotypes express only one class I molecule at high levels. The selection on a single MHC gene should be strong, in contrast to the situation in mammals. We have determined the peptide motifs for the dominant class I molecules from a number of chicken MHC haplotypes and found that they can explain the outcome of infections with a small virus. However, the strongest MHC association is the resistance of the chicken B21 haplotype to classical Marek's disease virus, a relatively large pathogen for which any MHC molecule should find peptides. In 40 chicken lines, the level of class I expression correlates with the level of MHC-determined susceptibility to Marek's disease, the most susceptible B19 with the highest expression and the most resistant B21 with the lowest expression. Thus, cell surface expression level of class I molecules appears to be a polymorphism under selection by infectious pathogens, just like peptide-binding specificity. We speculate that these expression level differences are another manifestation of the simple MHC of chickens, which in human and mouse haplotypes are averaged out.
Kaufman
J
J
Institute for Animal Health, Compton, Berkshire, U.K.
Salomonsen
J
J
D000818:Animals; D017951:Antigen Presentation / Q000235:genetics; D000956:Antigens, Viral / Q000276:immunology; D001665:Binding Sites; D002645:Chickens / Q000235:genetics* / Q000276:immunology; D019143:Evolution, Molecular; D005805:Genes, MHC Class I; D005802:Genes, MHC Class II; D006239:Haplotypes / Q000235:genetics; D015395:Histocompatibility Antigens Class I / Q000235:genetics / Q000276:immunology; D007113:Immunity, Innate / Q000235:genetics; D008285:Major Histocompatibility Complex / Q000235:genetics*; D008380:Marek Disease / Q000235:genetics / Q000276:immunology; D008957:Models, Genetic; D018448:Models, Immunological; D011110:Polymorphism, Genetic; D011201:Poultry Diseases / Q000235:genetics / Q000276:immunology*; D012641:Selection, Genetic; D013045:Species Specificity; D014714:Vertebrates / Q000235:genetics / Q000276:immunology; D014777:Virus Diseases / Q000235:genetics / Q000276:immunology*
D000956:Antigens, Viral; D015395:Histocompatibility Antigens Class I