Antibodies against C1q in anti-glomerular basement membrane nephritis

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Abstract
SUMMARY: The prevalence of antibodies against the collagen-like region of the subcomponent of the first component of complement, Clq, was investigated in 11 patients with anti-glomerular basement membrane (GBM) nephritis. Anti-C1q antibodies (anti-ClqAb) were detected in seven patients. IgG anti-ClqAb were found in four and IgA anti-ClqAb in five patients. During follow up of the patients a relationship was observed between the levels of IgG anti-ClqAb and the levels of anti-GBM antibodies (anti-GBMAb). Gelfiltration experiments indicated that both IgG anti-ClqAb as well as IgG anti-GBMAb were monomeric and that binding also occurred with the F(ab′)2 fragments of the antibodies. Although anti-ClqAb and anti-GBMAb are both directed against a collagen-like structure, it was demonstrated by means of inhibition experiments that anti-ClqAb and anti-GBMAb are directed against different antigenic sites. Comparison of patients with anti-GBM nephritis with and without anti-ClqAb revealed that there were no differences in disease activity or disease severity. Therefore, the results of this study suggest that anti-ClqAb do not play a direct pathogenetic role in anti-GBM nephritis.