Release of FcγRIIa2 by activated platelets and inhibition of anti-CD9-mediated platelet aggregation by recombinant FcαRIIa2

Abstract

Thrombin-activated human platelets and megakaryocyte cell lines release soluble FcγRII (FcγRIIa2) containing the extracellular and intracellular regions of FcγRIIa1, but lacking the transmembrane domain. Use of polyclonal antibodies directed either against the entire intracytoplasmic tail, or against a peptide located near the C-terminal part of the intracellular region of FcγRIIa2, showed the presence of both a complete form of FcγRIIa2 and a C-terminal truncated form in supernatants of platelets after release of their α granule contents and in culture supernatants of megakaryocyte cell lines. Furthermore, recombinant FcγRIIa2 inhibited in a dose-dependent manner Fc-dependent anti-CD9 antibody-induced platelet aggregation. Thus, release of FcγRIIa2 by activated platelets could play an important role in the regulation of platelet activation by immune complexes. © 1995 by The American Society of Hematology.