What chickens would tell you about the evolution of antigen processing and presentation

Outside of mammals, antigen processing and presentation have only been investigated in chickens. The chicken MHC is organized differently than mammals, allowing the co-evolution of polymorphic genes, with each MHC haplotype having a set of TAP1, TAP2 and tapasin alleles directed to high expression of a single classical class I molecule. However, the class I alleles vary in the size of peptide-binding repertoire, along with a suite of other properties. The salient features of the chicken MHC are found in many non-mammalian vertebrates, and are likely to have been set at the origin of the adaptive immune system of jawed vertebrates, with unrelated genes co-evolving to set up the original pathways. Half a billion years later, various features of presentation and resistance to disease still reflect this ancestral arrangement.