Dynamics of peripheral B and γδ T cells during postpartum and pregnancy in dairy cows

During postpartum, dairy cows experience immune modulation not only locally in the uterus, but also in the peripheral immune response in order to achieve implantation and pregnancy. This immune response is directly influenced by the hormonal milieu. The aim of this study was to analyze the number of circulating mononuclear immune cells, such as total T cells, CD4 T cells, CD8 T cells, γδ T cells, B cells, and monocytes, during mid- and late postpartum of dairy cows, taking into account the hormonal milieu. Dairy cows were grouped according to their parturition-conception interval (PCI), as follows: PCI shorter than 100 days (SPCI) and PCI longer than 170 days (LPCI). Percentages of peripheral mononuclear immune cells were evaluated by flow cytometry. Results showed that changes in the counts of total T cells, CD4 T cells and monocytes were not associated with the PCI or hormone concentrations. Differently, CD8 T cells at 45 days in milk were significantly higher in cows from the SPCI group than in those from the LPCI group. In addition, the main findings showed significant associations between the percentages of circulating B cells and γδ T cells and estradiol and progesterone concentrations during lactation. These associations between B cells, γδ T cells and the hormonal milieu may contribute to shorter PCIs through appropriate immunoregulation around conception and during pregnancy. This study provides, for the first time, a comprehensive characterization of mononuclear cell populations beyond 50 days postpartum, revealing their peripheral dynamics during the establishment of receptive reproductive conditions.