DNA topoisomerase I binding to fibroblasts induces monocyte adhesion and activation in the presence of anti–topoisomerase I autoantibodies from systemic sclerosis patients

Abstract

Objective. Systemic sclerosis (SSc) is an autoimmune disease characterized by fibrosis due to excessive and dysregulated collagen production by fibroblasts. Previously, we reported that anti-DNA topoisomerase I (anti-topo I) antibodies bound specifically to fibroblast surfaces; however, we had not identified their antigenic target. We undertook this study to characterize the target of anti-topo I antibodies on fibroblasts and the effects of their binding.Methods. Purified topo I or topo I released from apoptotic cells was tested for surface binding to a number of human cell types by cell-based enzyme-linked immunosorbent assay, flow cytometry, and indirect immunofluorescence. Antibodies purified from SSc patient and normal control sera were used to detect topo I binding. The consequences of topo I and anti-topo I binding to fibroblasts were assessed by coculture with THP-1 monocytes.Results. The autoantigen topo I itself was found to bind specifically to fibroblasts in a dose-dependent and saturable manner, where it was recognized by anti-topo I from SSc patients. The binding of anti-topo I subsequently stimulated adhesion and activation of cocultured monocytes. Topo I released from apoptotic endothelial cells was also found to bind specifically to fibroblasts.Conclusion. The findings of this study thus confirm and extend the findings of our previous study by showing that topo I binding to fibroblast surfaces is both necessary and sufficient for anti-topo I binding. Second, topo I-anti-topo I complex binding can then trigger the adhesion and activation of monocytes, thus providing a plausible model for the amplification of the fibrogenic cascade in anti-topo I-positive SSc patients.

Systemic sclerosis: a prototypic multisystem fibrotic disorder

“…Recent studies highlight the biological activities and potential pathogenic roles of autoantibodies in patients with SSc, suggesting that antibodies specific for fibroblasts, endothelial cells, and PDGF receptors might directly cause fibroblast or endothelial cell activation and contribute to tissue damage. For example, endothelial cell-specific antibodies in SSc induce adhe- sion molecule expression on endothelial cells, and antibodies specific for the PDGF receptor seem to stimulate expression of the genes encoding collagen in fibroblasts (49)(50)(51).…”

Association of Fcγ receptor IIIA variant with a subset of anti-topoisomerase I-positive patients in systemic sclerosis: a descriptive pilot study

“…In eVect, anti-topo I IgG are predominantly of the IgG1 subclass, which displays a diVerential aYnity for Fc RIIIA-158V and Fc RIIIA-158F allotypes [10] and whose titer strongly correlates with the severity of the disease [11]. More importantly, some anti-endothelial cell antibodies (AECA) found in the sera of dSSc patients do recognize topoisomerase I [12], and puriWed anti-topo I antibodies can bind to the surface of Wbroblasts and recruit Fc R-positive cells [13]. Overall, these studies support the observation of a link between anti-topo I positivity and FCGR3A-158V/F functional variants.…”

Early systemic sclerosis—opportunities for treatment

“…Some autoAbs detected in patients with SSc promote fibrosis and/or autoimmunity. Topoisomerase and anti-topoisomerase I autoAbs bind to fibroblasts and promote inflammation and fibrosis [30,31], and anti-matrix metalloproteinase-3autoAbs promote fibrosis [32], and functional autoAbs against CD22, a major inhibitory B cell coreceptor promote autoimmunity [21,33]. Stimulatory autoAbs against platelet-derived growth factor receptor were found to promote fibrosis [34], although this was not confirmed by others [35,36].…”