Some thoughts about what non-mammalian jawed vertebrates are telling us about antigen processing and peptide loading of MHC molecules.

The major histocompatibility complex (MHC) of mammals encodes highly polymorphic classical class I and class II molecules with crucial roles in immune responses, as well as various nonclassical molecules encoded by the MHC and elsewhere in the genome that have a variety of functions. These MHC molecules are supported by antigen processing and peptide loading pathways which are well-understood in mammals. This review considers what has been learned about the MHC, MHC molecules and the supporting pathways in non-mammalian jawed vertebrates. From the initial understanding from work with the chicken MHC, a great deal of diversity in the structure and function has been found. Are there underlying principles?