Identification of commonly recognized epitopes on a rare autoantigen: poly(ADP-ribose) polymerase.

To analyze mechanisms of autoantibody production, epitope mapping of a rare autoantigen, poly(ADP-ribose) polymerase, was performed. A cDNA fragment (1873 bp long), which was already confirmed to encode the autoepitopes of this protein, was subcloned into a protein expression plasmid pEX. Several deletion mutants were produced by enzymatic treatments of this construct. PCR-amplified cDNA fragments were also individually subcloned into this vector. The recombinant proteins produced in Escherichia coli by these vectors were tested for their respective antigenicities by immunoblotting. It was found that all positive sera tested (seven cases) strongly recognized common epitopes in a restricted region of the molecule. Furthermore, three out of the seven positive sera were found to recognize other parts of the molecule. The data suggest possible mechanisms for the formation of anti-poly(ADP-ribose) polymerase autoantibodies.