Main content area

TNFα-mediated plasminogen activation on neutrophils is involved in the high plasmin activity in mammary secretion of drying-off cows

Chou, Wen K., Yu, Ting C., Chen, Shuen E., Peh, Ho C., Liu, Wen B., Chen, Ming T., Nagahata, Hajime, Chang, Chai J.
Journal of dairy research 2009 v.76 no.4 pp. 459-468
dairy cows, immunity, secretion, mammary glands, cell physiology, biochemical pathways, tumor necrosis factor-alpha, neutrophils, plasminogen activator, resistance mechanisms, plasmin, plasminogen, mammary involution, in vitro studies
Interactions between inflammatory cytokines and plasminogen (Pg) activation system on immune cells are yet to be established. In previous studies we reported a somatic cell-associated elevation of proteolytic activity in mammary secretion of drying-off goats and cows. The purposes of the present study were to examine the role of TNF-α in polymorphonuclear neutrophil (PMN)-associated Pg activation, and the significance of this activation pathway for overall plasmin (Pm) activity in mammary secretion of drying-off cows. Results of experiments in vitro showed that the spontaneous Pg activation observed on fresh preparations of bovine blood PMN was completely blocked by anti bovine TNF-α antibody, and was further up-regulated by exogenous bovine TNF-α. Monitoring the parameters of mammary secretion of drying-off cows revealed that both somatic cell counts and differential PMN ratio was significantly elevated at weeks 1, 2 and 3 of milk stasis. Nevertheless, specific activity of soluble Pm in mammary secretion increased and the level of 17-kDa TNF-α decreased immediately following milk stasis. Iimmunoblotting revealed that although both 26-kDa pro-TNF-α and 17-kDa TNF-α were consistently present in somatic cells of mammary secretion collected at weeks 0, 1, 2 and 3 of milk stasis, only 26-kDa pro-TNF-α was present in somatic cells of milk during lactation. In-vitro assay indicated that cell-free mammary secretion of drying-off cows exerted no Pg activation bioactivity towards bovine blood PMN. Altogether, the current study suggests the existence of an active TNF-α-Pg-Pm autocrine/paracrine loop on the massively infiltrated PMN inside udders of drying-off cows, which involves extensive binding and internalization of 17-kDa TNF-α on PMN and consequently activation of Pg, resulting in high Pm activity and low 17-kDa TNF-α level in mammary secretion. These coordinated mechanisms may play a role in the defence of drying-off mammary gland.