Lupus-like disease in FcγRIIB-deficient C57BL/6 mice (Bolland and Ravetch, 2000) as well as the increased risk of SLE in homozygous carriers of the dysfunctional FcγRIIB I232T variant (Floto et al., 2005) clearly indicate a crucial role for this inhibitory receptor in the maintenance of humoral tolerance. Here, FCGR2B is linked to systemic lupus erythematosus.