The major histocompatibility complex in the chicken.

The chicken B complex is the first non-mammalian MHC characterized at the molecular level. It differs from the human HLA and murine H-2 complexes in the small size of the class I (B-F) and class II (B-L) genes and their close proximity. This proximity accounts for the absence of recombination between B-F and B-L genes and leaves no space for class III genes. Moreover the B-F and B-L genes are tightly linked to unrelated genes absent from mammalian MHCs, such as the polymorphic B-G genes and a member of the G protein beta subunit family. This linkage could form the basis for resistance to viral-induced tumors associated with some B complex haplotypes.