The chicken MHC (denoted the BF-BL region) has two classical MHC class I genes, BF1 and BF2 (formerly BF minor and major); only BF2 is expressed at a high level . Several MHC-I haplotypes have been recognized in the chicken and genetically defined . Unlike humans, however, chickens use a single dominantly expressed MHC-I from the B locus on each of their copies of