Measurement of soluble Fcγ receptor type IIIa derived from macrophages in plasma: increase in patients with rheumatoid arthritis

摘要

FcγRIII (CD16) is found in two alternative forms, a transmembrane FcγRIIIa expressed on NK cells and macrophages, and a glycosylphosphatidylinositol-linked FcγRIIIb present on neutrophils. Previously, we measured soluble FcγRIIIa (sFcγRIIIa) in plasma of NA(1 +, 2-) phenotyped donors with the anti-FcγRIII monoclonal antibody (MoAb) GRM1, which recognizes NA2-FcγRIIIb and FcγRIIIa. The level of sFcγRIIIa, as well as the total sFcγRIII (sFcγRIIIa plus sFcγRIIIb) in patients with rheumatoid arthritis (RA) was significantly higher than that in healthy controls. In this study, we measured sFcγRIIIa^Mφ in plasma with a newly developed anti-FcγRIII MoAb, MKGR14 (mIgM), which recognizes FcγRIIIa^Mφ specifically. From the recovery of purified sFcγRIIIa^Mφ, the amount of sFcγRIIIa^Mφ present was about half that of sFcγRIIIa^NK, and that of sFcγRIIIa was about 50 times lower than that of sFcγRIIIb in pooled plasma from healthy NA(1 +, 2-) phenotyped donors. The level of sFcγRIIIa^Mφ in RA patients was about four times higher than that in healthy controls. In RA patients, both the sFcγRIIIa^Mφ and sFcγRIIIa levels were increased as proportionally as the Lansbury Index. The sFcγRIIIa, but not sFcγRIIIa^Mφ levels, were increased directly proportional to C-reactive protein. sFcγRIIIa^Mφ may be a novel marker of disease activity in RA.