This is demonstrated by the increased binding of all four tested proteins (IgM, IgG, C4, C3) to these antigens from SLE sera (Fig 1), the differential effects of IgG binding on C4 deposition (Fig 2) and the inverse correlations with serum complement and dsDNA antibodies (Fig 3a and 3b). The gene discussed is C4A; the disease is systemic lupus erythematosus.