While the majority (>75%) of patients deficient in C4 develop lupus-like autoimmune diseases, some of which are associated with autoimmune uveitis (29, 30), suggesting that C4 is protective, it has also been reported that C4 levels are significantly elevated in patients with active Behçet’s disease (BD) (31), another autoimmune disease that frequently involves uveitis, compared to BD patients in remission or non-BD controls, suggesting that C4 is pathogenic. Here, C4A is linked to systemic lupus erythematosus.