FCGR2B and systemic lupus erythematosus: The effect of FcγRIIB on autoantibody production is B cell intrinsic, as overexpression of FcγRIIB on B cells from lupus-prone mice leads to improvement in the lupus phenotype (14, 15), and B cell–specific deletion of FcγRIIB leads to autoantibody production and a lupus phenotype (15, 16).