Protein tyrosine phosphorylation in leukocyte activation through receptors for IgG.

Membrane receptors for the Fc portion of immunoglobulin G (IgG) antibodies (Fc(gamma)Rs) are expressed on almost every type of hematopoietic cells, where they mediate a wide variety of effector functions. A high degree of structural heterogeneity exists among Fc(gamma)Rs. The biological significance of such heterogeneity is unknown, since the structural diversity does not appear to be reflected in the binding specificity nor in the effector functions that each distinct receptor is able to mediate. Recent work has emphasized the essential role of protein tyrosine phosphorylation in the initiation of transmembrane signaling by these receptors. In this article we review the role of protein tyrosine phosphorylation in signal transduction by the different types of Fc(gamma)Rs in order to assess to what extent the structural heterogeneity of this receptor family is related to different activation pathways utilized by each of its members.