AbstractObjective. To investigate the distribution of B cell autoepitopes of human DNA topoisomerase I (topo I), an autoantigen associated with scleroderma.Methods. A complementary DNA clone, T1B, was used to produce recombinant proteins of topo I as β‐galactosidase fusion proteins. Immunoreactivity to these fusion proteins was then tested in 35 anti–topo I–positive sera from patients with scleroderma, by immunoblotting, enzyme‐linked immunosorbent assay, and double immunodiffusion.Results. One epitope was found to be universally recognized by all sera tested. Thirty‐two of the samples recognized multiple antigenic regions, but sera from the remaining 3 patients recognized only this universal epitope, and in longitudinal studies of 1 of these 3 patients, the serum recognized only this epitope for more than 2 years, even though multiple, potent, antigenic regions were found on topo I.Conclusion. Recognition of multiple epitopes in most patients suggests that the topo I molecule itself would drive the autoimmunity on topo I. However, antigen‐driven autoimmunity could not explain the production of the monoreactive anti–topo I antibody seen in the 3 patients. We thus hypothesize that there is a process whereby recognition of the universal epitope by cross‐reaction develops into antigen‐driven autoimmunity.