C3 and rheumatoid arthritis: We found an increase in C3(H2O) levels in patients with active SLE (3,098 ± 382 ng/ml) and RA (4,234 ± 955 ng/ml) compared to healthy controls (HC; 1,999 ± 111 ng/ml) (Figure 5A), suggesting modestly higher baseline levels in patients' serum in these two disease states.