Background: Paraneoplastic pemphigus (PNP) serum preferentially reacts with periplakin and envoplakin, which are plakin family proteins localized to desmosomes and intermediate filaments. Recently, anti-periplakin antibodies were also detected in patients with idiopathic pulmonary fibrosis (IPF). Although previous epitope-mapping studies showed multiple epitopes in each protein, enzyme-linked immunosorbent assays have used several truncated, but not full-length, recombinant proteins. Methods: This study aimed to produce full-length biotinylated recombinant proteins of periplakin and envoplakin for detection of autoantibodies by immunoprecipitation and ELISA. Serum from a PNP patient who had been confirmed as carrying anti-periplakin and anti-envoplakin antibodies in our previous study was used as a positive control. Sera from 15 patients with IPF were analyzed for both antibodies by immunoprecipitation and by ELISA. Results: The PNP serum reacted strongly with the full-length recombinant proteins in immunoprecipitation and ELISA. Longitudinal serum samples from the PNP patient showed a clear decline of autoantibodies to both periplakin and envoplakin. None of the IPF sera showed both autoantibodies. Conclusions: We found that the detection of anti-periplakin and anti-envoplakin antibodies using full-length recombinant proteins is useful immunoprecipitation and ELISA.
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