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Abstract
Bovine leukemia virus (BLV) is estimated to infect over 83% of dairy herds and over 40% of all dairy cows in the United States. While, BLV only causes leukemia in a small proportion of animals, research indicates that BLV+ cattle exhibit reduced milk production and longevity that is distinct from lymphoma development. It is hypothesized that BLV negatively affects production by interfering with cattle immunity and increasing the risk of secondary infections. In particular, BLV+ cows demonstrate reduced circulating levels of both antigen-specific and total IgM. This study investigated possible mechanisms by which BLV could interfere with the production of IgM in naturally infected cattle. Specifically, total plasma IgM and the expression of genes IGJ, BLIMP1, BCL6, and PAX5 in circulating IgM+ B cells were measured in 15 naturally infected BLV+ and 15 BLV− cows. In addition, BLV proviral load (PVL) (a relative measurement of BLV provirus integrated into host DNA) and the relative expression of BLV TAX and 5 BLV microRNAs (miRNAs) were characterized and correlated to the expression of selected endogenous genes. BLV+ cows exhibited lower total plasma IgM and lower expression of IGJ, BLIMP1, and BCL6. While, BLV TAX and BLV miRNAs failed to correlate with IGJ expression, both BLV TAX and BLV miRNAs exhibited negative associations with BLIMP1 and BCL6 gene expression. The results suggest a possible transcriptional pathway by which BLV interferes with IgM production in naturally infected cattle.
Highlights
Bovine leukemia virus (BLV) is a δ-retrovirus that is the causative agent of enzootic bovine leukosis (EBL) [1]
We investigated whether BLV+ cows exhibited lower total IgM, as well as lower expression of genes associated with B-cell function and differentiation, IGJ, PAX5, BLIMP1, and BCL6
If lower observed IgM levels were the result of reduced IGJ expression in BLV+ cows, the total plasma IgM concentration should be reduced in those BLV+ cattle
Summary
Bovine leukemia virus (BLV) is a δ-retrovirus that is the causative agent of enzootic bovine leukosis (EBL) [1]. While the clinical stage of EBL is typically characterized by lymphosarcoma development, only a small percentage of infected cattle will progress to clinical disease [2]. Dairy producers rarely test for BLV infection on commercial dairy operations. It is estimated that at least 83% of US dairy herds are BLV-infected. The within-herd infection rate is often between 25 and nearly 50%, and approximately 40% of all dairy cows in the US are infected [3].
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