Several investigators reported that the complement split products like C3 fragment, C4d, C5a and C5b-9 could be detected in the urine of lupus nephritis (LN) patients, and found that the levels of C3d in urine was closely related to LN disease activity (Mejia-Vilet et al., 2021; Tamano et al., 2002). The gene discussed is C5; the disease is lupus nephritis.