FCGR2B and rheumatoid arthritis: We previously found that an inhibitory IgG Fc receptor IIB (FcγRIIB)-deficient mouse strain, originally established on 129 × C57BL/6 (B6) genetic background and backcrossed to B6 mice, designated KO1, spontaneously develops human RA-like disease features with marked synovitis and severe cartilage/bone destruction in multiple joints [10].