MOLECULAR CHARACTERIZATION OF MAJOR HISTOCOMPATIBILITY COMPLEX-(B) HAPLOTYPES IN BROILER-CHICKENS

In Leghorn (laying) chickens, susceptibility to a number of infectious diseases is strongly associated with the major histocompatibility (B) complex. Nucleotide sequence data have been published for six class I (B-F) alleles and for class II (B-L beta) alleles or isotypes hem 17 Leghorn haplotypes. It is not known if classical B-L or B-F alleles in broilers are identical, at the sequence level, to any Leghorn alleles . This report describes molecular and immunogenetic characterization o f two haplotypes from commercial broiler breeder chickens that were or iginally identified by serology as a single haplotype, but were differ entiated serologically in the present work. The two haplotypes, design ated B-A4 and B-A4variant, shared identical B-G restriction fragment l ength polymorphism patterns, but differed in one B-L beta fragment tha t cosegregated with the serological B haplotype. Furthermore, the nucl eotide sequences of the highly variable exons of an expressed B-L beta II family gene and BF gene from the two haplotypes were markedly diff erent from each other. Both the B-L beta II family and B-F gene sequen ces from the B-A4 haplotype were identical to the sequences obtained h em the reference B-21 haplotype in Leghorns; however, in the B-A4 hapl otype the B-L beta(21) and B-F-21 alleles were in linkage with B-G all eles that were not G(21). The nucleotide sequences from B-A4variant we re unique among the reported chicken B-L beta II family and B-F allele s.