The lupus nephritis (n = 17) group had higher levels of serum anti-C3aR antibodies than all other groups, including the following: the membranous nephropathy group (n = 18) (p < 0.001), focal and segmental glomerulosclerosis group (n = 25) (p < 0.001), IgA nephropathy group (n = 14) (p = 0.01), mesangial proliferative (non-IgA) glomerulonephritis group (n = 6) (p = 0.002), control group (n = 22) (p < 0.001), c-ANCA vasculitis group (n = 40) (p < 0.001), and p-ANCA vasculitis group (n = 16) (p = 0.01). Here, C3AR1 is linked to membranous glomerulonephritis.