Association of the amino acid motifs of BoLA-DRB3 alleles with mastitis pathogens in Japanese Holstein cows

The association of the polymorphism of bovine leukocyte antigen ( BoLA-DRB3 ) genes, identified by the polymerase chain reaction sequence-based typing (PCR-SBT) method, with resistance and susceptibility to mastitis caused by Streptococci , coagulase-negative Staphylococci, Escherichia coli and Staphylococcus aureus was investigated. Blood samples for DNA extraction were collected from 170 Holstein cows (129 mastitis and 41 healthy cows) from 5 districts in Chiba prefecture, Japan. Susceptibility or resistance to the mastitis-causing pathogens was thought to vary by the presence of amino acid substitutions at the 9, 11, 13, and 30 positions. DRB3*0101 and DRB3*1501 had amino acid motifs of Glu⁹, Ser¹¹, Ser¹³, and Tyr³⁰, and they were considered to have susceptibility to all 4 mastitis pathogens. In contrast, DRB3*1101 and DRB3*1401 had amino acid motifs of Gln⁹, His¹¹, Gly¹³, and His³⁰ in these positions, and they also had Val⁸⁶, so these alleles were considered to have resistance to Streptococcal and coagulase-negative Staphylococcal mastitis. However, in the case of Escherichia coli mastitis, amino acid substitutions at the 9, 11, 13, and 30 positions had little effect, but rather substitutions at the 47, 67 positions of pocket 7, and at the 71, 74 positions of pocket 4, Tyr⁴⁷, Ile⁶⁷, Ala⁷¹, and Ala⁷⁴, were associated with resistance. This motif was present in DRB3*1201 .