REGULATION OF CD11B CD18 EXPRESSION IN HUMAN NEUTROPHILS BY PHOSPHOLIPASE-A(2)/

Recent evidence suggests that phospholipase A2 (PLA2)-derived lipid me diators may regulate a number of neutrophil responses including degran ulation and adhesion. In view of the potential role of PLA2 in stimulu s-secretion coupling, we examined the relationship between PLA2 activa tion and the surface expression of CD11b/CD18 (MAC-1) in human polymor phonuclear leukocytes (hPMNL), including the functional consequences o f PLA2 inactivation on MAC-1 -dependent adhesion. The selective inhibi tion of PLA2 by the marine natural products manoalide (MLD) and scalar adial (SLD) blocks [H-3]arachidonic acid (AA) release in calcium ionop hore A23187-stimulated neutrophils, and also inhibits secretion of spe cific and azurophilic granule constituents. Additional studies demonst rate that MLD, SLD, and other less potent PLA2 inhibitors such as 4-br omophenacylbromide and nordihydroguiaretic acid inhibit the surface ex pression of MAC-1 (IC50: MLD, 0.33 muM; SLD, 0.23 muM; 4-bromophenacyl bromide, 2.8 muM; NDGA, 3.5 muM) at concentrations similar to those at which they inhibit [H-3]AA release. Inhibitors of cyclooxygenase, 5-l ipoxygenase, protein kinase C, or calcium channel antagonists have no effect on MAC-1 expression. PLA2 inactivation also prevents MAC-1 up-r egulation in hPMNL stimulated with FMLP, IL-8, TNF-alpha, PMA, or plat elet activating factor. In FMLP-stimulated hPMNL, under conditions in which no secondary granule constituents are secreted, MAC-1 and alkali ne phosphatase up-regulation from intracellular granules is inhibited by MLD and SLD. Functional assays also demonstrate that MLD and SLD bl ock MAC-1-dependent adhesion of activated neutrophils to keyhole limpe t hemocyanin at concentrations that block the surface expression of MA C-1. [H-3]AA release and MAC-1 expression in MLD and SLD-treated hPMNL could be recovered in the presence of 1 mM hydroxylamine in a time-de pendent fashion, consistent with reported data that MLD and SLD inacti vate PLA2 through Schiff base formation. In summary, these data emphas ize the role of PLA2 as a key regulator of MAC-1 expression in models of neutrophil adhesion.