Soluble Fcγ receptors II (FcγRII) are generated by cleavage of membrane FcγRII

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Abstract
This study describes the production of soluble FcγRII by a cell line, D1B1, obtained by transfection of mouse L cells with a murine β1 FcγRII cDNA. Upon incubation at 37 °C, radioiodinated D1B1 cells release a 39-kDa soluble FcγRII, reacting with the rat anti-mouse FcγRII monoclonal antibody 2.4G2, and binding to mouse IgG2a, IgG2b and IgG1 but not IgG3. In contrast to the transmembrane 50- to 70-kDa receptor, this soluble FcγRII does not react with antibodies directed against a peptide corresponding to the 15 carboxy-terminal intracytoplasmic amino acids of β FcγRII. N-Glycosidase F treatment generates a 18-kDa polypeptide. A 32- to 40-kDa soluble FcγRII, which resolves into 18.5- and 20-kDa polypeptides after deglycosylation, was also isolated from the culture medium of unlabeled D1B1 cells. Therefore, this study indicates that soluble FcγRII corresponding to the two extracellular domains of FcγRII are generated by cleavage of membrane FcγRII. Proteolysis occurs most probably at the vicinity of the transmembrane region of the receptor, around amino acids 165 to 180.