Tyrosine phosphorylation and Fc gamma receptor-mediated phagocytosis

Phagocytosis of IgG-opsonized particulate material in hematopoietic cells is mediated by Fc gamma receptors (Fc gamma Rs). Interaction of the receptors with Fc domains of IgG triggers transduction of phagocytic signal in which a key role is played by phosphorylation of tyrosine residues of the receptors. These residues are arranged into a specific motif (immunoreceptor tyrosine-based activation motif; ITAM) which is located either in the cytoplasmic part of Fc gamma RIIA or in gamma chains associated with Fc gamma RI and Fc gamma IIIA. The conserved tyrosine residues are phosphorylated by, and associate with, tyrosine kinases of Src and Syk families. Coordinated action of these components initiates numerous intracellular events leading finally to local rearrangement of the actin-based cytoskeleton and internalization of the particles.