Nucleotide sequence and polymorphism of MHC class II DQB exon 2 alleles in Chinese yakow (Bos grunniens × Bos taurus).

The objective of this study is to describe the gene characteristics of the bovine lymphocyte antigen (BoLA)-DQB exon 2 locus in Chinese yakow (Bos grunniens × Bos taurus) and to compare it with previously reported patterns in other bovidae species to investigate genetic factors for disease resistance. The exon 2 of the MHC class II DQB gene was cloned and sequenced. It was revealed by sequence analyses that there are 36 DQB exon 2 alleles among 44 Chinese yakow. These alleles exhibited a high degree of nucleotide and amino acid polymorphism with most amino acid variations occurring at positions forming the peptide-binding sites (PBS). The DQB loci were analysed for patterns of synonymous (dS ) and nonsynonymous (dN ) substitution. The Chinese yakow was observed to be under strong positive selection in the DQB exon 2 peptide-binding sites (dN = 0.147, P < 0.01). It appears that this variability among Chinese yakow confers the ability to mount immune responses to a wide variety of peptides or pathogens.