Both DQB genes are expressed in BoLA haplotypes carrying a duplicated DQ region

The objective of this study was to determine whether more than one DQB gene is expressed in three BoLA haplotypes that have a duplicated DQ region. Leukocyte mRNA from three animals genotyped at the BoLA-A, DQB, and DRB3 loci was used as template for reverse transcription-polymerase chain reaction (RT-PCR), cloning, and DNA sequencing. Five DQB alleles were identified. All cDNA clones were 564 base pairs (bp) in length, including 507 bp of nonprimer-derived sequence that contained the coding sequence for the full length of exon 2 and 74 amino acids of exon 3. Three alleles were assigned to the DQB1 locus and two were assigned to DQB2 on the basis of sequence comparisons with previously reported alleles. The expression of DQB1 and DQB2 in individual animals was examined by RT-PCR followed by double digestion of the 564 bp PCR products with Eco O109 I and Dra III in order to discriminate the DQB alleles. Evidence that DQB1 and DQB2 are both transcribed was obtained for three different BoLA haplotypes with DQB duplications, DQB10, DQB11C, and DQB12. These results suggest that the duplication or deletion event that gave rise to the DQB1 and DQB2 genes is a relatively recent event in the evolution of the cattle MHC.