Identification of a Universal B Cell Epitope on Dna Topoisomerase I, an Autoantigen Associated With Scleroderma

Abstract

Objective. 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.

A cross-reactive idiotype in scleroderma

“…In addition, these autoantibodies exhibit specific selection of autoantigens, either centromere proteins (CENPs) or topoisomerase-I, which are not major cell components, suggesting that these specific autoantigens are significantly involved in establishing the humoral response in scleroderma [30,31]. Many major proteins or epitopes for antitopoisomerase-I and anticentromere antibodies have been identified since our first descriptions [30][31][32][33][34][35][36][37][38][39][40].…”

“…The shared autoepitope could be the primary target [32,33] that begins a restricted B cell response [41][42][43]. Consequently, one may hypothesize that a process of 'epitope spreading' is responsible for recognition of epitopes (within the CENP-B or topoisomerase-I) [32,[35][36][37][38][39][40], or other autoantigen proteins (CENP-A and or C) [33,43]. Centromere proteins and topoisomerase-I are antigenic in rabbits and mice [32,44].…”

Detection of anti-topoisomerase I antibodies using a full length human topoisomerase I recombinant protein purified from a baculovirus expression system

“…The availability of cloned material for human topo I has provided a rich source of recombinant fusion proteins for use in diagnostic assays [8][9][10][11][12][13][14][15], Most such studies have used partial length topo I fusion proteins expressed in prokaryotic systems, which have the potential disadvantage of excluding important antigenic epitopes, or may give rise to false positive results by including non-relevant bacterial antigens. In the current study we have used a full length human topo I protein purified from a eukaryotic baculovirus system as the source of antigen in a Correspondence: Dr Neil John McHugh, Royal National Hospital for Rheumatic Diseases, Upper Borough Walls, Bath BAl IRL, UK.…”

Autoepitopes of the 52‐kd ss‐a/ro molecule

“…It is interesting to note that a similar universal epitope has been found on topoisomerase I, an autoantigen associated with scleroderma (36). Why this Al-unique epitope is universally recognized is still to be resolved, but one possible reason might be that this epitope appears to have a highly antigenic structure.…”