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Bovine leukemia virus (BLV) is the causative agent of enzootic bovine leukosis. Polymorphism in bovine leukocyte antigen (BoLA)‐DRB3 allele can influence the host immune response to pathogens, including BLV. However, association between specific BoLA‐DRB3 alleles and BLV proviral load (PVL), which is a useful index for estimating disease progression and transmission risk, in Vietnamese cattle are unknown. Here, association study of BoLA‐DRB3 allele frequency between cattle with high or low PVL demonstrated BoLA‐DRB3*12:01 associates with high PVL in Vietnamese Holstein Friesian (HF) crossbred cattle. This is the first study to demonstrate that BoLA‐DRB3 polymorphism confers susceptibility to BLV high PVL in HF crossbred kept in Vietnam. Our results may be useful in disease control and eradiation for BLV through genetic selection. [ABSTRACT FROM AUTHOR]

Bovine leukemia virus (BLV) causes enzootic bovine leucosis. Host genetic heterozygosity at the major histocompatibility complex can enhance the ability to combat infectious diseases. However, heterozygote advantage is loci specific and depends on disease type. Bovine leukocyte antigen (BoLA)‐DRB3 polymorphisms are related with BLV‐infection outcome; however, whether BoLA‐DRB3 heterozygotes have an advantage against BLV‐induced lymphoma and proviral load (PVL) remains unclear. By analyzing 1567 BLV‐infected individuals, we found that BoLA‐DRB3 heterozygous status was significantly associated with lymphoma resistance irrespective of cattle breeds (p < 0.0001). Similarly, decreased PVL was observed in BoLA‐DRB3 heterozygotes (p = 0.0407 for Holstein cows; p = 0.0889 for Japanese Black cattle). Our report provides first evidence of BoLA‐DRB3 heterozygote advantage against BLV infection outcome. [ABSTRACT FROM AUTHOR]

The genetic diversity of the BoLA‐DRB3 gene has been reported in different cattle breeds owing to its central role in the immune response. However, it is still unknown in hundreds of cattle breeds, especially native populations. Here, we studied BoLA‐DRB3 genetic diversity in Highland Creole cattle (CrAl) from Western Bolivia, raised at altitudes between 3800 and 4200 m. DNAs from 48 CrAl cattle were genotyped for BoLA‐DRB3 exon 2 alleles using polymerase chain reaction‐sequence‐based typing (PCR‐SBT). The results were compared with 1341 previously reported data from Tropical Creole cattle and other breeds raised in the region. Twenty‐three BoLA‐DRB3 alleles were identified in CrAl, including the BoLA‐DRB3*029:02 variant previously detected in other Creole cattle. Observed and expected heterozygosity were 0.87 and 0.93, respectively. Nucleotide diversity and the number of pairwise difference values were 0.078 and 19.46, respectively. The average number of nonsynonymous and synonymous substitutions were 0.037 and 0.097 for the entire BoLA‐DRB3 exon 2, and 0.129 and 0.388 for the antigen‐binding site, respectively. Venn analysis and the review of the IPD‐MHC database and the literature showed that 2 of 64 alleles were only detected in CrAl, including BoLA‐DRB3*029:01 previously reported in African cattle and *048:01 detected in Philippine cattle. Two additional alleles, BoLA‐DRB3*007:02 and *029:02, were only present in CrAl and Lowland Creole cattle. Principal Component Analysis (PCA) showed that Bolivian Creole cattle breeds were closely located but they were distant from the Colombian Hartón del Valle Creole. FST analysis showed a low degree of genetic differentiation between Highland and Lowland Bolivian Creole cattle (FST = 0.015). The present results contribute to increasing our knowledge of BoLA‐DRB3 genetic diversity in cattle breeds. [ABSTRACT FROM AUTHOR]