The avian MHC

The major histocompatibility complex (MHC) is a genetic region encoding classical class I and class II molecules that are highly polymorphic, are widely and strongly expressed, present peptides to T cells (as well as being recognised by natural killer cells), and therefore play crucial roles in infectious disease resistance and vaccine response, as well as autoimmunity and reproduction. The BF-BL region of the B locus is the chicken MHC, and is much smaller and simpler than the MHC of typical mammals. The results of this simplicity have included new insights into the structure, function and evolution of the MHC and MHC molecules. Examination of MHC genes and functions suggests that most birds share many of the properties first discovered in the chicken MHC. Other properties have altered in a few lineages, particularly within passerines, which have been intensively studied for some aspects of immunity and reproduction in wild bird populations.