The role of individual Fc gamma receptors in aggregated IgG-stimulated protein tyrosine phosphorylation in the human neutrophil.

Having previously shown that heat-aggregated IgG stimulates a significant increase in tyrosine phosphorylation in the human neutrophil, we next sought to determine the role of individual Fc gamma receptors in this response. Specific cross-linking of Fc gamma RII reproduced the phosphorylation observed with heat-aggregated IgG treatment and monoclonal antibodies recognizing the ligand binding domain of Fc gamma RII efficiently blocked the heat-aggregated IgG induced response. Thus engagement of Fc gamma RII alone appears sufficient to mimic the heat-aggregated IgG stimulation. Similar experiments carried out with antibodies specific for Fc gamma RIII suggested that Fc gamma RII and Fc gamma RIII may cooperate in the phosphorylation response. The activation of a tyrosine kinase by Fc gamma R engagement was demonstrated by the specific immunoprecipitation of several tyrosine phosphorylated proteins from lysates of neutrophils following treatment with aggregated IgG.