In human neutrophils the binding to immunocomplexes induces the tyrosine phosphorylation of Fc gamma RII but this phosphorylation is not an essential signal for Fc-mediated phagocytosis

It has been recently suggested that protein tyrosine phosphorylation is involved in Fc gamma Rs-mediated signalling. In this paper we have investigated if in human neutrophils a tyrosine phosphorylation of Fc gamma RII takes places after the binding with immunocomplexes and if this phosphorylation plays a role in phagocytic signal. The immunoprecipitation with mAb anti-Fc gamma RII of lysates of neutrophils challenged in suspension with insoluble immunocomplexes (IIC) or sheep erythrocytes opsonized with IgG (E-IgG), followed by immunoblotting with anti-phosphotyrosine antibody, demonstrated that Fc gamma RII was tyrosine phosphorylated. When neutrophils were pretreated with different doses of tyrosine kinase inhibitors, genistein or erbstatin, the phosphorylation of Fc gamma RII induced by IIC or E-IgG was dose dependently inhibited. In these conditions both genistein and erbstatin failed to inhibit the phagocytosis of E-IgG. These results demonstrated that in human neutrophils in suspension the binding to Fc of IgG induces a tyrosine phosphorylation of Fc gamma RII but this phosphorylation is not an essential signal for phagocytosis of IgG-opsonized particles.