Patients with IgA nephropathy have circulating anti-basement membrane antibodies reacting with structures common to collagen I, II, and IV.

It has recently been shown that patients with IgA nephropathy have circulating IgA antibodies against extracts of human glomerular basement membrane. The present study extends those observations and demonstrates by using ELISA and immunoblotting techniques that patients with IgA nephropathy have circulating IgA antibodies against collagen IV alpha chains. The antigenicity of the alpha chains could be destroyed by digestion with collagenase, which indicates that the antigenic site(s) is located on the triple helical part of collagen IV. Furthermore, it was shown by inhibition tests that the IgA antibodies are directed against epitopes also present in collagen I and II isolated after pepsin digestion.