Polymorphism in BoLA-DRB3 exon 2 correlates with resistance to persistent lymphocytosis caused by bovine leukemia virus.

The relationship between polymorphism of the bovine lymphocyte Ag (BoLA)-DRB3 gene and resistance and susceptibility to persistent lymphocytosis (PL) caused by bovine leukemia virus (BLV) was investigated. Exon 2 of the BoLA-DRB3 gene was cloned from animals with BoLA haplotypes previously found to be associated with resistance and susceptibility to PL. Sequence analysis revealed the presence of the amino acids Glu-Arg (ER) at putative Ag binding residues 70 and 71 only in BoLA haplotypes associated with resistance to PL. This correlation was confirmed in a case control study (n = 26) using an allele-specific polymerase chain reaction for the detection of ER at residues 70-71. These results provide a molecular basis for Ir gene control of resistance and susceptibility to PL and suggest that the cellular immune response is important in preventing the in vivo spread of BLV infection.