Enhanced production of bovine tumor necrosis factor-α during the periparturient period

This study examined the production of tumor necrosis factor (TNF-α) by mononuclear cells isolated from peripheral blood and supramammary lymph nodes of periparturient and mid to late lactating dairy cows. Monocyte-enriched cell populations were stimulated with lipopolysaccharide (LPS) and analyzed for TNF-α concentrations. Flow cytometric analysis was performed to determine the frequencies of relevant cell populations. Isolated mononuclear cells from periparturient dairy cows produced significantly higher levels of TNF-α than mid to late lactating dairy cows regardless of tissue location. A corresponding increase in the frequency of monocytes also was observed in tissue samples obtained from periparturient animals. The higher proportion of monocytes capable of producing TNF-α in the periparturient dairy cow may account for the increased levels of this potent mediator. Within the periparturient period, peripheral blood mononuclear cells were found to produce significantly less TNF-α than cells isolated from mammary lymph nodes. However, flow cytometric analysis revealed similar monocyte concentrations in both the peripheral blood and mammary lymph node. This indicates that the differences in cytokine production may be due to variations in monocyte activation state with respect to tissue location. It is possible that greater potential to produce TNF-α during the periparturient period may contribute to the severe acute phase response of the mammary gland to coliform infections during this time. Limiting TNF-α production by monocytes, particularly within the mammary gland, may reduce the severity of clinical coliform mastitis in periparturient dairy cattle.