Earlier studies have shown that 56R+/− mice on the C57BL/6 wt background produce autoreactive IgM and some IgG Abs (47), and that the introduction of the 56R allele into lupus-prone Fcgr2b−/− mice lead to increased IgG class switched autoAbs, particular of the 56R allele (45, 46). This evidence concerns the gene FCGR2B and systemic lupus erythematosus.