Characterization of Fc gamma receptors on human megakaryocytes.
Megakaryocyte and platelet Fc gamma receptors (FcR) are of importance in the pathophysiology of immune complex-mediated thrombocytopenias such as heparin-induced thrombocytopenia. In this study, Fc gamma R proteins and mRNAs in normal human megakaryocytes were examined. Fc gamma R proteins were studied with immunocytochemical staining, dual colour flow cytometry and immunoprecipitation using monoclonal antibodies against Fc gamma R I, Fc gamma R II and Fc gamma R III. Fc gamma R mRNAs were measured with biotinylated cDNA of oligonucleotide probes using a novel quantitative in situ hybridization technique. Using these techniques, Fc gamma R II protein and mRNA, but not Fc gamma R I and Fc gamma R III proteins and transcripts were detected in megakaryocytes. Further, transcript analysis showed that megakaryocytes contain only the transcript of Fc gamma R IIA gene but no transcripts of Fc gamma R IIB nor Fc gamma R IIC genes; Fc gamma R IIA transcripts with and without the transmembrane (TM) exon are present in approximately equal proportions. In contrast, neutrophils and macrophages also contain Fc gamma R IIA transcript but Fc gamma R IIA transcript with the TM exon predominates suggesting cell lineage-specific Fc gamma R IIA expression. Fc gamma R IIA transcript lacking the TM exon predicts the presence of a potential soluble form of Fc gamma R in platelets and megakaryocytes which may have a physiological role as it can compete with the membrane-bound Fc gamma R IIA for binding of IgG-containing immune complexes and thus protect these cells from excessive binding and injurious effects of immune complexes.
Wu
Z
Z
Centre for Thrombosis and Vascular Research, University of New South Wales, Randwick, Australia.
Markovic
B
B
Chesterman
C N
CN
Chong
B H
BH
D001483:Base Sequence; D019070:Cell Lineage; D005091:Exons; D005434:Flow Cytometry; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008264:Macrophages / Q000737:chemistry; D008280:Magnetics; D008533:Megakaryocytes / Q000737:chemistry*; D008863:Microspheres; D008969:Molecular Sequence Data; D009504:Neutrophils / Q000737:chemistry; D011233:Precipitin Tests; D012333:RNA, Messenger / Q000032:analysis*; D011961:Receptors, Fc / Q000032:analysis* / Q000235:genetics
D012333:RNA, Messenger; D011961:Receptors, Fc