The enzyme NADPH oxidase is regulated by phospholipase D in intact neutrophils and is activated by phosphatidic acid (PA) plus diacylglycerol (DG) in cell-free systems. We showed previously that cell-free NADPH oxidase activation by these lipids involves both protein kinase-dependent and -independent pathways. Here we demonstrate that only the protein kinase-independent pathway is operative in a cell-free system of purified and recombinant NADPH oxidase components. Activation by PA ؉ DG was ATP-independent and unaffected by the protein kinase inhibitor staurosporine, indicating the lack of protein kinase involvement. Both PA and DG were required for optimal activation to occur. The drug R59949 reduced activation of NADPH oxidase by either arachidonic acid or PA ؉ DG, with IC 50 values of 46 and 25 M, respectively. The optimal concentration of arachidonic acid or PA ؉ DG for oxidase activation was shifted to the right with R59949, indicating interference of the drug with the interaction of lipid activators and enzyme components. R59949 inhibited the lipid-induced aggregation/sedimentation of oxidase components p47 phox and p67 phox , suggesting a disruption of the lipidmediated assembly process. The direct effects of R59949 on NADPH oxidase activation complicate its use as a "specific" inhibitor of DG kinase. We conclude that the protein kinase-independent pathway of NADPH oxidase activation by PA and DG involves direct interaction with NADPH oxidase components. Thus, NADPH oxidase proteins are functional targets for these lipid messengers in the neutrophil.The NADPH oxidase (the respiratory burst enzyme) in phagocytic cells produces superoxide (O 2 . ) 1 by catalyzing electron transfer from NADPH to molecular oxygen upon cell stimulation (1-3). This enzyme plays important roles in host defense against infection and in tissue damage due to inflammation (1-5). In addition, NADPH oxidase-like enzymes are present in a variety of other cell types, where the oxygen radicals formed may have signaling roles (5, 6). The enzyme in phagocytes consists of the membrane-bound heterodimeric flavocytochrome b 558 (gp91 phox and p22 phox ) and four cytosolic proteins (p47 phox , p67 phox , p40 phox , Rac1/2) (2-4, 7). Components must assemble in the membrane for the enzyme to become active (2-4, 7). The activation of NADPH oxidase is initiated by receptor-ligand interaction and involves complex intracellular signaling events. These include the activation of protein kinases to phosphorylate cellular proteins and NADPH oxidase components (2, 8) and the generation of various lipid second messengers (AA by phospholipase A 2 (9); DG by phospholipase C or PA phosphohydrolase; PA by phospholipase D or DG kinase (10, 11)). In cell-free systems, these lipids can induce activation of the enzyme (12-17). AA exerts its effect by directly acting on enzyme components (18 -22). PA has been shown to partially activate purified flavocytochrome b 558 (23), suggesting it interacts with this protein. It is not known whether DG has any direct effe...

SUMMARYWe reported earlier that neonatal monocyte-derived macrophages (MDM) could not be fully activated with IFN-g, a finding that could not be attributed to lower expression of IFN-g receptors on the neonatal cells. In this study we explored elements of IFN-gR-mediated signalling in cord monocytes and MDM. Intracellular expression of STAT-1 was analysed by flow cytometry. We have assessed phosphorylation of STAT-1 by using MoAbs that distinguish native and phosphorylated forms of STAT-1 on a discrete cell basis. Using MoAbs against the native form of STAT-1 revealed comparable expression of this protein in cord and adult cells (both monocytes and MDM). However, STAT-1 phosphorylation in response to IFN-g was significantly decreased in neonatal monocytes (P , 0´05) and MDM (P , 0´01) compared to adult cells (n . 5 for each). These data suggest deficient cytokine-receptor signalling in neonatal mononuclear phagocytes exposed to IFN-g. We propose that decreased STAT-1 phosphorylation and activation may represent developmental immaturity and may contribute to the unique susceptibility of neonates to infections by intracellular pathogens.

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We reported earlier that monocytes and macrophages from patients with type I Gaucher disease have a decreased capacity to generate superoxide anion (O(2)(-)) on stimulation with opsonized S. aureus or formyl-methionyl-leucyl-phenylalanine. In this study, various forms of the cell-free assay system were used to probe the hypothesis that glucocerebroside (GC) accumulating in Gaucher patients' phagocytes may interfere with the activation of NADPH oxidase. Xanthine/xanthine oxidase assay was applied to explore the possibility that GC may scavenge O(2)(-). We found that addition of GC to the crude, semirecombinant or fully purified cell-free systems inhibited activation of NADPH oxidase in a concentration-dependent manner. The inhibitory effect of GC could be overcome by increased concentrations of p47(phox) and p67(phox). In contrast, O(2)(-) generation was not decreased by GC added to the assembled, catalytically active enzyme complex. In the xanthine/xanthine oxidase system, GC had no effect on the generation of O(2)(-). These data indicate that assembly of the respiratory burst oxidase of phagocytic cells may be a possible target of the pathologic actions of GC.