Abstract
Fc γRIIA (CD32), a conventional type I transmembrane protein, and Fc γRIIIB (CD16B), which has a glycan phosphatidylinositol (GPI) membrane anchor, are both expressed on human neutrophils. Although some details remain to be elucidated, signaling following crosslinking of Fc γRIIA requires the activation of tyrosine kinases of both Src-family kinases and Syk, resulting in tyrosine phosphorylation of Shc, phospholipase C γ isozymes, and a [Ca 2+] i transient. Ligation of neutrophil Fc γRIIIB triggers a [Ca 2+] i transient, and degranulation, although probably not ADCC or an oxidative burst. However, the mechanism for signal transduction by Fc γRIIIB, which lacks a transmembrane domain, is not known. Fc γRIIA and Fc γRIIIB appear to synergize with each other, leading to suggestions that the GPI-anchored Fc γRIIIB utilizes the Fc γRIIA signaling apparatus. The relevance of proposed specialized membrane domains enriched in GPI-anchored proteins, sphingomyelin and glycolipids to the signaling properties of Fc γRIIIB likewise remains to be explored.
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