Formula omitted]-Dependent stimulation of leukotriene B4 synthesis by human neutrophils (PMN) is synergistically enhanced by tumour necrosis factor α and low dose diacylglycerol

Abstract

Unopsonised zymosan particles bind to the CD11b CD18 integrin on human neutrophils (PMN) and are phagocytosed. Binding stimulates the release of leukotriene (LT) B4. The present study examined the effect on this interaction of two agents that ‘prime’ PMN for augmented responses to a variety of agonists. The cell permeable diacyl glycerol, 1,2-dioctanoyl-glycerol (DiC8) and TNFα each increased CD11b CD18 expression on PMN [maximal at 10 −9 M TNFα or 10 −8 M DiC8]. There was a decrease, however, in CD11b CD18 expression above 10 −8 M DiC8, which was not observed at high concentrations of TNFα. Pre-treatment with either DiC8 or TNFα dose-dependently augmented the zymosan-stimulated release of LTB4 from PMN. DiC8 and TNFα in combination, however, synergistically increased LTB4 release. In contrast, at concentrations above 10 −8 M DiC8, whether in the presence or absence of TNFα, LTB4 release was inhibited and this was ameliorated by protein kinase C inhibitors. The response to neither TNFα nor DiC8 (below 10 −8 M) was kinase inhibitor sensitive. Doses of DAG, which activate protein kinase C, inhibit CD11b CD18 -dependent responses by down-regulating receptor expression. In contrast, the mechanisms of TNFα and low dose DAG ‘priming’ are not clear but are independent of PKC activation. The synergy between these two priming agents, however, suggests independent, complementary signalling pathways that provide a novel, potentially important mechanism for the control of PMN CD11b CD18 integrin-dependent activation.