TRANSMEMBRANE SIGNALING PATHWAYS INVOLVED IN PHAGOCYTOSIS AND ASSOCIATED ACTIVATION OF NADPH OXIDASE MEDIATED BY FC-GAMMA-RS IN HUMAN NEUTROPHILS

We have previously shown that in neutrophils classical transmembrane s ignaling consisting of increased [Ca2+]i and hydrolysis of phospholipi ds was not essential for phagocytosis mediated by more than one recept or (yeast-IgG, yeast-C3b/bi, yeast-Con A). This work deals with the ro le of this transmembrane signaling in phagocytosis of erythrocyte (E) IgG, which is mediated only by receptors for IgG (FcgammaRs). The inge stion of E-IgG was associated with an increase in [Ca2+]i and producti on of inositol phosphates, phosphatidic acid, diacylglycerol, and arac hidonic acid, via activation of phospholipases C, D and A2. Related to the same number of particles ingested, the respiratory burst and the transmembrane signaling during phagocytosis of E-IgG were much smaller than during phagocytosis of yeast-IgG. In Ca2+-depleted neutrophils, where the increase in [Ca2+]i and hydrolysis of phospholipids were lac king, the phagocytosis of E-IgG was depressed by about 60%; the respir atory burst was also depressed due to the decrease of ingestion and of stimulation of NADPH oxidase by residual phagocytosis. Pertussis toxi n (PT) did not inhibit the phagocytosis of E-IgG but depressed by abou t 40% the stimulation of lipidic transmembrane signaling and the respi ratory burst in normal neutrophils. In Ca2+-depleted neutrophils the t oxin was without effect on ingestion and respiratory burst. Staurospor ine did not inhibit the ingestion of E-IgG in normal and Ca2+-depleted neutrophils but depressed by 30-40% the respiratory burst in normal a nd not in Ca2+-depleted neutrophils. Genistein, an inhibitor of tyrosi ne kinase, did not inhibit the ingestion of E-IgG but depressed by 30- 40% the respiratory burst both in normal and Ca2+-depleted neutrophils . These results demonstrate the following findings in human neutrophil s. (1) Contrary to the phagocytosis mediated by more than one receptor (yeast-IgG, yeast-Con A, yeast-C3b/bi), the transmembrane signaling i nvolving increase in [Ca2+]i and hydrolysis of phospholipids plays a r ole in the phagocytosis and respiratory burst mediated by FcgammaRs al one. Thus, different signal transduction pathways can be involved in p hagocytosis and associated respiratory burst depending on the receptor or combination of receptors activated. (2) FcgammaRs alone promote ph agocytosis with two signaling pathways independent of and dependent on [Ca2+]i changes and phospholipid hydrolysis and insensitive to PT, st aurosporine, and genistein. (3) The signaling pathways promoting phago cytosis triggered by FcgammaRs alone are in some way, or at some step, different from those that activate the respiratory burst.