2000 Volume 13 Issue 2 Pages 95-102
The mechanism of IgA deposition on glomerular mesangial matrix in IgA nephropathy is unknown. We have demonstrated that IgA was incorporated into the extracellular matrix when mixture of IgA and cathepsin D-digested fibronectin fragments was reacted with confluent cell layers of cultured human fibroblasts for 3 hr and was cultured with medium for an additiona1 24 hr. Since we have also demonstrated that IgA 1-associated fibronectin fragments was present in patient's serum, we examined in this paper if patient's IgA obtained by affinity chromatography using jacalin-agarose is able to deposit in extracellular matrix in association with fibronectin, which might be co-purified along with IgA. Samples obtained from serum were applied to the culture system of above described. In all of 10 patients with IgA nephropathy, but not in 10 normal controls, IgA was deposited in extracellular matrix of cultured human fibroblast. The coarse and punctate clusters of IgA staining by immunofluorescence was obtained, and the pattern was similar to that seen in the experiment using mixture of IgA and fibronectin fragments. The staining was abolished by treatment of patients' samples with anti-human fibronectin monoclonal antibodies, suggesting that IgA deposition on extracellular matrix is associated with fibronectin. Furthermore, an addition of cathepsin D-digested fibronectin to the samples from patients augmented the size and the number of IgA deposition on extracellular matrix. When samples were sequentially reacted to the cell layers just after a series of sample application was finished, IgA staining was also augmented. These results suggest that the complex of IgA and fibronectin fragments may co-exist in serum from patients with IgA nephropathy and contribute to IgA deposition onto mesangial matrix through the mechanism of assembly of exogenous fibronectin into extracellular matrix.
