Genetic mechanisms of resistance and susceptibility to leukemia in Ayrshire and black pied cattle breeds determined by allelic distribution of gene Bola-DRB3

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.