CR3, FcγRIIA and FcγRIIIB induce activation of the respiratory burst in human neutrophils: the role of intracellular Ca 2+, phospholipase D and tyrosine phosphorylation

Human neutrophils express two different types of phagocytic receptors, complement receptors (CR) and Fc receptors. In order to characterize the different signaling properties of each receptor we have used non-adherent human neutrophils and investigated CR3, FcγRIIA and FcγRIIIB 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-FcγRIIIB Pansorbins induced about half of the response induced by anti-CR3 Pansorbins, whereas anti-FcγRIIA Pansorbins induced an even weaker signal. However, FcγRIIA induced strong phosphorylation of p72 syk whereas FcγRIIIB 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 FcγRIIA and FcγRIIIB as well as CR3. This shows that tyrosine phosphorylation of p72 syk is an early signal in the cascade induced by FcγRIIA but not by CR3.