Bovine CD8+ suppressor lymphocytes alter immune responsiveness during the postpartum period

This study examined the immunoregulatory role of CD8+ lymphocytes during the postpartum period. Peripheral blood cells were isolated from postpartum and mid to late lactating animals. Flow cytometric analysis was performed to determine the frequencies of relevant cell populations. Depletion of CD8+ lymphocytes from whole cultures significantly decreased proliferation and cytotoxic ability of cells isolated from mid to late lactating animals. Enrichment of whole cultures with CD8+ lymphocytes further decreased their proliferative ability but pure CD8+ lymphocyte had increased cytotoxic activity. In contrast, neither depletion nor enrichment of whole cultures with CD8+ lymphocytes altered the already diminished proliferative responses of cells isolated from postpartum cows. No cytotoxic activity was observed by cells isolated from postpartum animals. Cultures from mid to late lactating cows mainly expressed IFN-γ mRNA where as IL-4 mRNA was mainly expressed by cultures isolated from postpartum animals. Flow cytometric analysis revealed that CD8+ lymphocytes have a high level of activation and expression of the β-chain during the postpartum compared with the mid to late lactating period. These data indicate that CD8+ lymphocytes are of the suppressor compared to the cytotoxic nature immediately following parturition.