ENHANCED PRODUCTION OF BOVINE TUMOR-NECROSIS-FACTOR-ALPHA DURING THE PERIPARTURIENT PERIOD

This study examined the production of tumor necrosis factor (TNF-alpha ) by mononuclear cells isolated from peripheral blood and supramammary lymph nodes of periparturient and mid to late lactating dairy cows. M onocyte-enriched cell populations were stimulated with lipopolysacchar ide (LPS) and analyzed for TNF-alpha concentrations. Flow cytometric a nalysis was performed to determine the frequencies of relevant cell po pulations. Isolated mononuclear cells from periparturient dairy cows p roduced significantly higher levels of TNF-alpha than mid to late lact ating dairy cows regardless of tissue location. A corresponding increa se in the frequency of monocytes also was observed in tissue samples o btained from periparturient animals. The higher proportion of monocyte s capable of producing TNF-alpha in the periparturient dairy cow may a ccount for the increased levels of this potent mediator. Within the pe riparturient period, peripheral blood mononuclear cells were found to produce significantly less TNF-alpha than cells isolated from mammary lymph nodes. However, flow cytometric analysis revealed similar monocy te 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 loc ation. It is possible that greater potential to produce TNF-alpha duri ng the periparturient period may contribute to the severe acute phase response of the mammary gland to coliform infections during this time. Limiting TNF-alpha production by monocytes, particularly within the m ammary gland, may reduce the severity of clinical coliform mastitis in periparturient dairy cattle.