Anti-DNA topoisomerase I autoantibodies bind directly to the cell surface of fibroblasts in patients with systemic sclerosis

Objective

Fibroblasts play a crucial role in the development of systemic sclerosis (SSc), and antifibroblast antibodies (AFAs) capable of inducing a proinflammatory phenotype in fibroblasts have been detected in SSc sera. In the present study, we examined the prevalence of AFAs in SSc and other diseases, and the possible correlation between AFAs and known antinuclear antibody specificities in SSc patients.

Methods

Sera from 99 patients with SSc, from 123 patients with other autoimmune and nonautoimmune diseases, and from 30 age-matched and gender-matched healthy controls were examined. The AFA prevalence was assessed by flow cytometry and further characterized by indirect immunofluorescence, ELISA and immunoblotting. Anti-topoisomerase I (anti-topo I) from SSc sera was purified by affinity chromatography on topoisomerase I.

Results

AFAs were more common in SSc patients (26%) than in any other diseases studied. The presence of AFAs was significantly associated with pulmonary involvement and death. SSc AFA-positive sera bound to all human and rodent fibroblasts tested but not to human primary endothelial or smooth muscle cells. All SSc AFAs strongly reacted with topoisomerase I by ELISA and immunoblotting. The binding intensity of SSc AFAs correlated strongly with reactivity against topoisomerase I on immunoblots of fibroblast extracts, and with the immunofluorescent pattern typical of anti-topo I on permeabilized cells. Total IgGs and affinity-purified anti-topo I from AFA-positive SSc sera were found to react with the surface of unpermeabilized fibroblasts by flow cytometry and by immunofluorescence and confocal microscopy.

Conclusion

This is the first report establishing that AFAs in SSc are strongly correlated with anti-topo I and, furthermore, that anti-topo I itself displays AFA activity by reacting with determinants at the fibroblast surface.