Isolation of cDNAs for two distinct human Fc receptors by ligand affinity cloning.

Two cDNA clones encoding different but related receptors for immunoglobulin G constant domains were isolated from cDNA expression libraries by a ligand-mediated selection procedure ('affinity cloning'). Because both of the receptors encoded by the cDNAs react with CDw32 monoclonal antibodies, and both show the appropriate IgG binding affinity, both appear to be forms of the receptor formerly thought to be a single species called FcRII. The extracellular domains encoded by the isolated clones are closely related to the murine IgG2b/1 beta receptor extracellular domains, but the intracellular domains are unrelated. The receptors expressed in COS cells show a preference for IgG1 among IgG subtypes and no affinity for IgM, IgA or IgE. Abundant expression of the RNAs was detected in myeloid cell lines and placenta.