BoLA-DRB3 Polymorphism Associated with Bovine Leukemia Virus Infection and Proviral Load in Holstein Cattle in Egypt

Abstract

Bovine leukemia virus (BLV) is the etiological agent of enzootic bovine leukosis, the most prevalent neoplastic disease of cattle worldwide. The immune response to BLV and disease susceptibility and resistance in cattle are strongly correlated with the bovine leukocyte antigen (BoLA)-DRB3 allelic polymorphism. BLV infection continues to spread in Egypt, in part because the relationships between BLV infection, proviral load in Egypt, and BoLA-DRB3 polymorphism are unknown. Here, we identified 18 previously reported alleles in 121 Holstein cows using a polymerase chain reaction sequence-based typing method. Furthermore, BoLA-DRB3 gene polymorphisms in these animals were investigated for their influence on viral infection. BoLA-DRB3*015:01 and BoLA-DRB3*010:01 were identified as susceptible and resistant alleles, respectively, for BLV infection in the tested Holsteins. In addition, BoLA-DRB3*012:01 was associated with low PVL in previous reports but high PVL in Holstein cattle in Egypt. This study is the first to demonstrate that the BoLA-DRB3 polymorphism confers resistance and susceptibility to PVL and infections of BLV in Holstein cattle in Egypt. Our results can be useful for the disease control and eradication of BLV through genetic selection.

Keywords: BLV; BLV infection; BoLA-DRB3; Holstein cattle; association study; polymorphism; proviral load.

Figure 1

Comparison of proviral load (PVL) in blood from BLV-positive cows. BLV PVLs calculated using CoCoMo-qPCR-2. LPVL: cows with low PVL (34 ≤ PVL ≤ 85 copies per 10⁵ cells), n = 14 cows; MPVL: cows with moderate PVL (89 ≤ PVL ≤ 25,858 copies per 10⁵ cells), n = 17 cows; HPVL: cows with high PVL (35,138 ≤ PVL ≤ 98,725 copies per 10⁵ cells), n = 14 cows. Black bars show the main BLV PVL values.