Reactivity against the epitope region 4 (ER 4) on the DNA topoisomerase I molecule as a new predictor for progressive restrictive pulmonary function abnormality in patients with systemic sclerosis

Our previous studies showed that serum anti-DNA topoisomerase I (topo I) antibody is associated with pulmonary interstitial fibrosis and restrictive pulmonary function abnormality in patients with systemic sclerosis (SSc). We also demonstrated that at least four epitopes exist on the topo I molecule, and a region from amino acid residues 658-700 of the topo I molecule is referred to as epitope region 4 (ER 4). In this study, we examined the reactivity against ER 4 in sera from 28 anti-topo I antibody positive patients with SSc by immunoblotting. We then clarified the clinical significance of this reactivity against ER 4 in terms of the progressive restrictive pulmonary function abnormality. The reactivity against ER 4 was found to be positive in 15 patients (ER 4 +) and negative in 13 patients (ER 4 —). Differences in gender, mean age at onset, and mean observation period were not significant among these groups. Restrictive pulmonary function abnormality defined as results of percent vital capacity (%VC) less than 80% was found in 12 ER 4+patients and 8 ER 4-patients, although this difference was not significant. However, when progressive restrictive pulmonary function abnormality is defined as both %VC less than 80% and 10% reduction during their observation period, this abnormality was found exclusively in 9 ER 4 + patients. This difference was significant (p < 0.01). Moreover, this progressive abnormality was found in spite of therapy such as prednisolone and D-penicillamine. These results indicated that the reactivity against ER 4 is a useful predictor for the progressive restrictive pulmonary function abnormality in patients with SSc.