Differential expression of Fc gamma RIIA, Fc gamma RIIB and Fc gamma RIIC in hematopoietic cells: analysis of transcripts.

Fc gamma receptors (Fc gamma R) are glycoproteins that function in the immune response through their ability to bind the Fc portion of immunoglobulin G. Of the three human Fc gamma R classes, Fc gamma RII is most widely distributed among hematopoietic cells and is the only Fc gamma R class present on platelets and megakaryocytes. There are three different genes coding for Fc gamma RII: Fc gamma RIIA, Fc gamma RIIB and Fc gamma RIIC. Alternative splicing of at least two of these genes results in the production of multiple transcripts. Combining Northern blot analysis with reverse transcription-PCR, we analyzed steady state levels of Fc gamma RII mRNA in the megakaryocytic, myeloid and lymphoid lineages. We determined that megakaryocytic cells predominantly contain Fc gamma RIIA mRNA; Fc gamma RIIA transcripts with and without the transmembrane exon (Fc gamma RIIa1 and Fc gamma RIIa2, respectively) are present in comparable amounts. In contrast, B lymphocytes do not express Fc gamma RIIA mRNAs, but do contain both Fc gamma RIIB transcripts, Fc gamma RIIb1 and Fc gamma RIIb2, as well as the Fc gamma RIIC transcript, Fc gamma RIIc. Myelomonocytic cells contain mRNAs from all three Fc gamma RII genes, predominantly the Fc gamma RIIa1 transcript, both Fc gamma RIIb1 and Fc gamma RIIb2 transcripts and Fc gamma RIIc. Lineage-specific expression of the Fc gamma RII genes implies both differential regulation of expression and differential function in diverse cells.