Sequences and diversity of 17 new Ovar-DRB1 alleles from three breeds of sheep

To investigate the genetic diversity of the sheep MHC (Ovar) class II DRB1 locus, we amplified exon 2 of Ovar-DRB1 alleles by polymerase chain reaction (PCR) and determined the nucleotide sequences of both resultant strands after cloning. In our study of a total of 97 sheep of three breeds, namely, Suffolk, Cheviot and Corriedale, we identified 18 previously published alleles and 17 new alleles. These alleles were 83.4 to 94.1% identical at the nucleotide level and 71.4 to 90.9% identical at the amino acid level to Ovar-DRB1*0101. We identified six new alleles in Cheviot sheep and 11 new alleles in Suffolk sheep. Furthermore, we identified 15, 6 and 1 allele in Suffolk, Cheviot and Corriedale sheep, respectively, that have only been found in these breeds to date. Analysis of the frequencies of the various Ovar-DRB1 alleles in each breed indicated that Ovar-DRB1*0702 was the most frequent allele in Suffolk sheep (23.9%), Ovar-DRB1*0203 was the most frequent allele in Cheviot sheep (27.5%) and Ovar-DRB1*0201 was the most frequent allele in Corriedale sheep (25.0%). A comparative analysis of the positions of polymorphic residues in the first extracellular domain of the DRB genes of sheep, humans and mice revealed an extraordinary similarity amongst the positions of polymorphic residues that are associated with the antigen recognition site (ARS). Moreover, the extent of polymorphism seems to be similar in sheep, humans and mice.