In the herds of Ayrshire and Black Pied cattle breeds of Russian selection, comparative analysis of allelic distribution of
BoLA-DRB3 was performed in animal groups with different status of persistent
lymphocytosis (PL) caused by the bovine leukemia virus (BLV). Alleles were typed by PCR-RFLP. Different spectra of
BoLA-DRB3 alleles mediating susceptibility and resistance to
leukemia were detected in the studied breeds. The role of
amino acid motives in beta 1 domain of
BoLA-DRB3 antigens was confirmed: ER (in positions 70-71), in resistance to
leukemia and VDTY and VDTV (75-78), in susceptibility to
leukemia. The nucleotide sequence of allele BoLA-DRB3.2*7 with deletion of
codon 65, which resulted in the changed conformation of the corresponding
antigen molecule, was associated with resistance to PL. Cows of Black Pied and Ayrshire breeds with genotypes coding VDTY/VDTV (RR = 11.67, P = 0.014) and VDTY/VDTY (RR = 4.71, P = 0.022), respectively, were shown to be susceptible to PL. The role of heterozygosity level was demonstrated (estimated by BoLA-DRB3 alleles and by
amino acid motives in positions 75-78 of the
antigen) as an unspecific factor of resistance to PL. The lowest heterozygosity level by
amino acid motives (75-78) was revealed in PL animals, for which sample inbreeding coefficients were detected: F = 0.324 and F = 0.084 in Ayrshire and Black Pied breeds, respectively.