Fc gamma receptors activate different protein kinase C isoforms in human neutrophils

Receptors for FcγR on human neutrophils constitute an important mechanism for the recognition of opsonized microorganisms and for cell activation. Human neutrophils express 2 FcγR: FcγRIIa and FcγRIIIb. Previously, it has been reported that activation of each FcγR induces different neutrophil responses by triggering distinct signal transduction pathways, although what particular signal transduction pathway is triggered by each FcγR has not been completely elucidated. It has also been reported that PKC is important for FcγR signaling and that each FcγR may activate different PKC isoforms. Therefore, we explored whether FcγRIIa or FcγRIIIb activates different PKC isoforms in human neutrophils and whether activation of these PKC isoforms results in different neutrophil responses. Hence, either FcγRIIa or FcγRIIIb was selectively cross-linked by monoclonal antibodies in the presence or absence of pharmacological inhibitors for various PKC isoforms. Inhibition of PKCα or PKCδ blocked FcγRIIa-induced reactive oxygen species productions. In contrast, inhibition of PKCα and/or PKCβ blocked FcγRIIIb-induced reactive oxygen species production. Also, inhibition of all PKC isoforms did not affect the FcγRIIa-induced increase in intracellular calcium concentration ([Ca2+]i), while inhibition of PKCα blocked FcγRIIIb-induced increase in [Ca2+]i. Additionally, inhibition of PKCδ blocked FcγRIIa-induced ERK phosphorylation, while inhibition of PKCα prevented FcγRIIIb-induced ERK phosphorylation. These results suggest that both FcγRIIa and FcγRIIIb activate unique PKC isoforms and that activation of these PKC isoforms can selectively regulate different neutrophil functions. These findings also reinforce the idea that each FcγR in human neutrophils triggers distinct signal transduction pathways.