👤 María Carolina Ceriani

Bovines infected by bovine leukemia virus (BLV) are characterized by presenting low proviral load (LPL) or high proviral load (HPL). It is reported that animals with HPL in peripheral blood mononuclear cells (PBMCs) present a decrease in apoptosis, an increase in viability and the proliferation rate, while animals that maintain an LPL have an intrinsic ability to control the infection, presenting an increased apoptosis rate of their PBMCs. However, there is little information on the effect of BLV on these mechanisms when the virus infects somatic milk cells (SC). This study investigates the mechanisms underlying apoptosis in milk and blood from BLV-infected animals with HPL and LPL. Relative levels of mRNA of tumor necrosis factor-α (TNF-α), TNF receptor 1 (TNF-RI), TNF receptor 2 (TNF-RII), anti-apoptotic B-cell lymphoma 2 protein (Bcl-2), and pro-apoptotic Bcl-2-like protein 4 (Bax) were measured in SC and PBMCs using quantitative reverse transcription-polymerase chain reaction (RT-qPCR) assay. A significant decrease in the expression of TNF-α in SC from HPL animals vs non-infected bovines was observed, but the infection in SC with BLV did not show a modulation on the expression of TNF receptors. A significant increase in TNF-RI expression in PBMCs from HPL bovines compared to LPL bovines was observed. No significant differences in PBMCs between HPL and LPL compared to non-infected animals concerning TNF-α, TNF-RI, and TNF-RII expression were found. There was a significant increase of both Bcl-2 and Bax in SC from LPL compared to non-infected bovines, but the Bcl-2/Bax ratio showed an anti-apoptotic profile in LPL and HPL bovines compared to non-infected ones. Reduced mRNA expression levels of Bax were determined in the PBMCs from HPL compared to LPL subjects. In contrast, BLV-infected bovines did not differ significantly in the mRNA expression of Bax compared to non-infected bovines. Our data suggest that the increased mRNA expression of Bax corresponds to the late lactation state of bovine evaluated and the exacerbated increase of mRNA expression of Bcl-2 may be one of the mechanisms for the negative apoptosis regulation in the mammary gland induced by BLV infection. These results provide new insights into the mechanism of mammary cell death in HPL and LPL BLV-infected bovine mammary gland cells during lactation. Show less

The retrovirus bovine leukemia virus (BLV) might produce abnormal immune function, associated with susceptibility to developing other infectious diseases, including mastitis. This study aimed to determine the proviral load and cytokines gene expression in peripheral blood mononuclear cells (PMBC) and milk somatic cells (SC) in BLV-infected and non-infected cattle. Of 27 BLV-infected cows in PBMC, 17 (62.96%) had a high proviral load (HPL), and 10 (37.04%) had a low proviral load (LPL). All SC samples had low proviral load (LPL-SC). Higher IFN-γ and IL-10 expression, and lower IL-12 and IL-6 expression, were found in PBMC from BLV-infected compared to BLV non-infected cattle. Moreover, higher IFN-γ, IL-12, and IL-6 expression, and lower IL-10 expression were observed in cattle with LPL-PBMC compared to HPL-PBMC. In milk samples, lower IFN-γ and higher IL-12 mRNA expression were observed in LPL-SC compared to BLV non-infected cattle in SC. IL-10 and IL-6 expression mRNA was significantly lower in LPL-SC than in SC from BLV non-infected cattle. This study shows that milk SC maintains lower proviral load levels than PBMC. This first report on Th1 and Th2 cytokines expression levels in SC may be relevant to future control strategies for BLV infection, mastitis, and udder health management. Show less