Characterization of an acidic nuclear protein recognized by autoantibodies in sera from patients with IgA nephropathy

A nuclear antigen is recognized by autoantibodies in the sera of some patients with IgA nephropathy. Using these autoantibodies as a reagent, this antigen was purified 77.2-fold by ammonium sulfate fractionation, DEAE chromatography and Sepharose 6BCL gel filtration. The antigenicity of this antigen was sensitive to trypsin but resistant to RNase and DNase, suggesting that the antigenic determinant resided in protein and not nucleic acids. This antigen was inactivated at 56 degrees C for 3 h. Isoelectrophoretic focussing showed that the pI was below 4. The immunoblotting (Western transfer) assay showed a single polypeptide (69,000 Daltons) which proved to be a reactive antigen.