CLONING AND CHARACTERIZATION OF FC-ALPHA-RB, A NOVEL FC-ALPHA RECEPTOR (CD89) ISOFORM EXPRESSED IN EOSINOPHILS AND NEUTROPHILS

The Fc receptor for IgA (Fc alpha R, CD89) is a transmembrane glycopro tein found on monocytes, macrophages, neutrophils, and eosinophils. He re we describe the characterization of a novel isoform of the Fc alpha R cloned from a human eosinophil cDNA library. This clone, Fc alpha R b, lacks the exon encoding the transmembrane/intracellular region of w ild type Fc alpha R, which is replaced by 23 new amino acids. Expressi on of Fc alpha Rb mRNA could be detected in eosinophils and neutrophil s. IIA1.6 murine pro-B cells transfected with Fc alpha Rb cDNA secrete high levels of the protein, but also a substantial amount of Fc alpha Rb is expressed at the cell membrane. Membrane-bound Fc alpha Rb bind s IgA-coated beads equally well as wild type Fc alpha R. Surface expre ssion is not affected by phosphatidyl inositol phospholipase C, indica ting that glycosyl phosphatidyl inositol-linkage of Fc alpha Rb is not likely. In IIA1.6 cells expressing Fc alpha Rb and FcR gamma, which i s necessary for signal transduction by wild type Fc alpha R, no tyrosi ne phosphorylation or Ca2+-mobilization could be observed after recept or cross-linking. These results indicate that Fc alpha Rb is likely to have a different function than wild-type Fc alpha R receptor. (C) 199 6 by The American Society of Hematology.