FCGR2B and systemic lupus erythematosus: Notably, slightly elevated proteinuria (Figure 1F) and prominent mesangial staining (Figure 1J, thick arrow) was demonstrated in PBS-control FcgRIIb-/- mice without renal injury by other parameters (Figure 1G–J), implying a pre-existing lupus-induced renal injury in 24-wk-old FcgRIIb-/- mice.