Identification and phylogenetic analysis of 15 MHC class II DRB1 beta1 expressed alleles in a ewe-lamb flock.

Ovar-DRB1 is part of the major histocompatibility complex (MHC) class II of sheep and functions by presenting extracellular-derived peptides to the immune system. Although there are over 100 different Ovar-DRB1 DNA sequences reported in GenBank, only two Ovar-DRB1 mRNA sequences have been reported. As a first step in understanding MHC Class II function as it relates to disease progression in sheep, Ovar-DRB1 transcripts encoding the peptide-binding site or the first domain (beta1) of Ovar-DRB1 in a 32-ewe-lamb flock were identified and characterized by using reverse transcriptase-polymerase chain reaction, cloning, sequencing, and phylogenetic analysis. Fourteen new Ovar-DRB1 beta1 cDNA sequences out of a total of 15 Ovar-DRB1 beta1 cDNA sequences in a ewe-lamb flock of 32 sheep were identified. One Ovar-DRB1 beta1 cDNA sequence was 100% identical to M93432, one of the two Ovar-DRB1 mRNA sequences reported in GenBank. Twelve out of 15 Ovar-DRB1 beta1 cDNA sequences were 100% identical to the corresponding previously reported Ovar-DRB1 genomic DNA sequences, indicating that these Ovar-DRB1 genomic DNA sequences are also transcribed. One of three of the remaining Ovar-DRB1 beta1 cDNA sequences, DRB1*07012, had a synonymous substitution resulting in an identical deduced amino acid sequence to DRB1*0701. Two of the remaining three Ovar-DRB1 beta1 cDNA sequences had nucleotide differences and subsequent deduced amino acid sequence differences when compared to known Ovar-DRB1 beta1 genomic DNA sequences, and therefore, DRB1*0206 and DRB1*0353 represent new Ovar-DRB1 beta1 expressed alleles. Phylogenetic analysis of the 15 Ovar-DRB1 beta1 cDNA sequences revealed that DRB1*0206 had a strong phylogenetic relationship to DRB1*0203, and DRB1*0353 had a strong phylogenetic relationship to DRB1*0303.