Differential expression of class I MHC (B-F) loci in broiler breeder haplotypes

The chicken MHC contains two B-F (class I MHC) loci. In experimental lines of Leghorn chickens, it has been reported that the B-F alpha I locus is the major sequence that is expressed, with the other locus being expressed less well (minor) or not at all (4). We have characterized the MHC in three commercial broiler breeder lines of chickens by RT-PCR amplification of B-F and B-LB mRNA from peripheral blood mononuclear cells.. Several of the broiler breeder haplotypes correspond to standard haplotypes of Leghorns, on the basis of sequence identity of major B-LB genes, and in some cases, identical B-G RFLP patterns. In some of these broiler haplotypes, however, the predominantly expressed B-F sequence matched the minor B-F sequence found in Leghorn haplotypes. Four broiler breeder haplotypes (BA5, BA12, BC5, and BD7) expressed predominantly a sequence that was identical in the alpha 1 and alpha 2 domains to the minor sequence expressed in standard B4 and B21 haplotypes, but differed among themselves by I to 5 nucleotides in the alpha 3 domain. Two other broiler haplotypes with B-LB sequences matching that of standard B6 haplotype, expressed predominantly a B-F sequence identical to the minor B-F sequence of standard B6.