Indeed, 40-wk-old FcγRIIb−/− mice showed lupus characteristics, including increasing levels of serum anti-dsDNA and proteinuria with proliferative glomerulonephritis in renal histology (Supplementary Fig. 1A-C), spontaneous elevation of serum cytokines, as evaluated by tumor necrosis factor alpha (TNFa) and interleukin-6 (IL-6), and an extracellular traps biomarker (serum citrullinated histone H3; CitH3) (Supplementary Fig. 1D-G). Here, FCGR2B is linked to proliferative glomerulonephritis.