C3 and systemic lupus erythematosus: Our analysis of the subset of serum samples from patients with SLE for which corresponding disease-activity data were available (that is, SLEDAI scores, anti-dsDNA Abs, C3 and C4 levels, and ESR) indicates that elevated heterotrimer levels may be associated with increasing SLE disease activity (Supplemental Tables 1 and 2 in Additional file 2).