First Identification of BoLA-DRB3 Alleles Associated with Differential Susceptibility to Bovine Leukemia Virus Infection and Proviral Load in Chinese Holstein Cattle

Bovine leukemia virus (BLV), the most prevalent neoplastic disease of cattle worldwide, is the causative agent of enzootic bovine leukosis. Polymorphisms in the bovine leukocyte antigen (<i>BoLA</i>)<i>-DRB3</i> gene can influence host immune responses to pathogens, including BLV. However, the associations between specific <i>BoLA-DRB3</i> alleles, BLV proviral load (PVL), a useful index for estimating disease progression and transmission risk, and BLV infection in Chinese cattle remain unknown. In this study, we identified 28 previously reported alleles in 289 Holstein cattle from Shandong Province, China, using polymerase chain reaction sequence-based typing. We further investigated whether <i>BoLA-DRB3</i> polymorphisms influenced infection status and identified <i>BoLA-DRB3*011:01</i> as an allele associated with susceptibility to BLV infection. An association analysis of allele frequencies between cattle with high and low PVL demonstrated that <i>BoLA-DRB3*014:01:01</i> was significantly associated with low PVL. Farms with a higher frequency of cattle carrying <i>BoLA-DRB3*014:01:01</i> had lower mean PVL values than farms with a lower frequency, indicating that resistant alleles are linked to low PVL levels. To our knowledge, this is the first study to demonstrate that <i>BoLA-DRB3</i> polymorphisms associate with differential susceptibility to BLV infection and PVL in Holstein cattle in China. These findings may contribute to BLV control and eradication efforts through genetic selection.