CR3, FcγRIIA and FcγRIIIB induce activation of the respiratory burst in human neutrophils:: the role of intracellular Ca2+, phospholipase D and tyrosine phosphorylation

Human neutrophils express two different types of phagocytic receptors, complement receptors (CR) and Fc receptors. Tn order to characterize the different signaling properties of each receptor we have used non-adherent human neutrophils and investigated CR3, Fc gamma RIIA and Fc gamma RIIIB for their signaling capacity. Selective activation of each receptor was achieved by coupling specific antibodies to heat-killed Staphylococcus aureus particles, Pansorbins, through their Fc moiety. Despite the fact that these particles are not phagocytosed, we show that addition of Pansorbins with anti-CD18 antibodies recognizing CR3 induced prominent signals leading to a respiratory burst. Stimulation with anti-Fc gamma RIIIB Pansorbins induced about half of the response induced by anti-CR3 Pansorbins, whereas anti-Fc gamma RIIA Pansorbins induced an even weaker signal. However, Fc gamma RIIA induced strong phosphorylation of p72(syk) whereas Fc gamma RIIIB induced only a very weak p72(syk) phosphorylation. During CR3 stimulation no tyrosine phosphorylation of p72(syk) was seen. Both phospholipase D and NADPH oxidase activities were dependent on intracellular calcium. This is in contrast to tyrosine phosphorylation of p72(syk) that occurred even in calcium-depleted cells, indicating that oxygen metabolism does not affect p72(syk) phosphorylation. Inhibitors of tyrosine phosphorylation blocked the respiratory burst induced by both Fc gamma RIIA and Fc gamma RIIIB as well as CR3. This shows that tyrosine phosphorylation of p72(syk) is an early signal in the cascade induced by Fc gamma RIIA but not by CR3. (C) 1999 Elsevier Science B.V. All rights reserved.