Development of an ELISA for detection of autoantibodies to nuclear matrix protein 2

Objectives. Autoantibodies characterizing certain forms of inflammatory myopathy, which are myositis-specific autoantibodies, are useful in the diagnosis and prediction of prognosis in DM/PM. This study aimed to identify a subset of DM patients who have anti-nuclear matrix protein 2 (anti-NXP-2) antibodies by using biotinylated recombinant proteins, and to clarify the clinical features of DM patients with these antibodies. Methods. Sera from 170 Japanese patients with CTDs including 106 with DM, 8 with PM, 21 with SLE, 20 with SSc, 15 with myositis overlap syndrome and 20 healthy controls were screened for anti-NXP-2 antibodies by our novel ELISAs. Positive sera were further examined by immunoprecipitation. Results. Sera from 6 of the 170 patients with CTDs were confirmed to be positive for anti-NXP-2 antibodies. These six positives were from female patients, with five of the six sera being from adult DM patients and only one of the six being from 1 of the 12 JDM patients. All these patients had myositis. None of the anti-NXP-2-positive patients had interstitial lung disease, but one patient was complicated with ovarian cancer. Conclusion. Our newly developed ELISA is applicable for the measurement of anti-NXP-2 antibodies. The results show that anti-NXP-2 antibodies, which have been characterized in JDM, exist in adult DM patients. Further studies using large populations are necessary to elucidate the characteristic clinical features and the prognosis of patients with anti-NXP-2 antibodies, especially for adult patients.