Bovine leukemia virus (BLV) is caused by a deltaretrovirus and has been associated with immunosuppression as well as comorbidities such as bovine mastitis, the costliest disease in the dairy sector. However, no previous study has explored at the synergistic immunosuppressive effect of the peripartum period with an immunosuppressive viral disease such as BLV. Thus, our study explored the effect of BLV infection in the periparturient period on the expression of PD-1 and CTLA-4 in blood T lymphocytes, and the impact of BLV infection on the rate of new intramammary infections during the early lactation. Here, we found that BLV-infected dairy cows always had a statistically significant higher expression of CTLA-4 and PD-1 in blood T cells. Furthermore, our findings indicated that BLV infection prolongs immunosuppression in dairy cows during the periparturient period by sustaining higher expression of immunological checkpoints in T cells. In addition, BLV-infected dairy cows have a higher rate of new intramammary infections during early lactation. Thus, our study provides new insights of the immunosuppressive effect of BLV on the most critical period of the cows’ life with marked detrimental effect on protective T-cell immunity and comorbidities, such as bovine mastitis.

牛白血病病毒（BLV）是由δ逆转录病毒引起的，与免疫抑制以及牛乳腺炎等合并症有关，牛乳腺炎是乳制品行业中最昂贵的疾病。然而，之前没有研究探讨围产期与 BLV 等免疫抑制病毒性疾病的协同免疫抑制作用。因此，我们的研究探讨了围产期BLV感染对血T淋巴细胞中PD-1和CTLA-4表达的影响，以及BLV感染对哺乳早期新发乳房内感染率的影响。在这里，我们发现感染 BLV 的奶牛血液 T 细胞中 CTLA-4 和 PD-1 的表达始终具有统计学上显着的较高水平。此外，我们的研究结果表明，BLV 感染通过维持 T 细胞中免疫检查点的较高表达来延长围产期奶牛的免疫抑制。此外，感染BLV的奶牛在泌乳早期新发乳房内感染的比例较高。因此，我们的研究提供了关于 BLV 对奶牛生命最关键时期的免疫抑制作用的新见解，对保护性 T 细胞免疫和合并症（如牛乳腺炎）具有显着的有害影响。