Circulating immune complexes and the nephropathy of cystic fibrosis

To explore the putative nephropathic role of Pseudomonas-associated immune complexes, the authors measured the quantity of immune complexes in sera obtained, before death, from 20 patients with cystic fibrosis, and compared these findings with the histologic features of the lesions and with immunofluorescence patterns of kidney tissue obtained at autopsy. The immune complexes were measured by solid-phase C1q (C1q immune complex) and conglutinin to detect complexes containing IgM, IgA, and IgG. Elevated levels of C1q immune complex (13 patients) suggested the possibility of renal deposition of C3 (P less than 0.005) and IgM (P less than 0.05). The only three patients with IgA tissue deposits had elevated levels of C1q immune complex with normal IgA immune complexes. No other assay findings correlated with the immunofluorescence findings. Despite the prominent C3 in tissue deposits, the histologic features were not significantly associated with the results of the immune complex assays. This study indicates that complement-activating IgM-containing complexes can be deposited in renal tissues of patients with cystic fibrosis, but their nephropathogenicity is doubtful. These observations of kidney lesions, which diminish the injurious role of immune complexes in cystic fibrosis, may be relevant to an understanding of the pathogenesis of the lung lesions, which recent studies have linked to the presence of immune complexes.