OCCURRENCE OF ANTI-C1Q ANTIBODIES IN IGA NEPHROPATHY

Background. The pathogenic mechanisms and the antigens involved in the establishment and progress of IgA nephropathy are unknown. As antibod ies against C1q have been reported to correlate with SLE nephritis, we analysed the occurrence of these antibodies in IgA nephropathy in ord er to investigate the possibility of pathogenetic similarities in thes e renal disorders. Methods. The occurrence of IgA- and IgG anti-C1q an tibodies (anti-C1q) were determined by ELISA in patients with IgA neph ropathy (n = 36) and SLE nephritis (n = 37), diseases both known to be associated with circulating immune complexes. Levels of these antibod ies were also determined in two other glomerular diseases, i.e. idiopa thic membranous glomerulonephritis (n = 7) and minimal change disease (n = 2), in which circulating immune complexes are usually not present , and in 40 healthy controls. Results. IgA anti-C1q was observed in in creased titres in 11/36 of the patients with IgA nephropathy, in 2/37 of the patients with SLE nephritis (both with proliferative disease) a nd in 1/9 of the patients with membranous and minimal change disease ( P<0.001). Increased titres of IgG anti-C1q were observed in 1/36 of th e patients with IgA nephropathy, in 17/37 of the patients with SLE nep hritis and in 0/9 of the patients with membranous and minimal change d isease (P<0.001). There were no correlations between the levels of ant i-C1q antibodies and clinical parameters such as degree of proteinuria , haematuria, or renal function. Nor was there any correlation to the concentration of C3a and the terminal complement complex (TCC) in pati ents with IgA nephropathy. Conclusions. The occurrence of anti-C1q ant ibodies in both IgA nephropathy and SLE nephritis, albeit of different predominating isotypes, indicates the possibility of a similar pathog enic mechanism involved in these renal disorders. The occurrence of Ig A anti-C1q antibodies in patients with IgA nephropathy has to our know ledge not previously been reported.