Topoisomerase 1-DNA complexes are preferentially recognised by a subset of anti-topoisomerase 1 autoantibodies and their corresponding B cell receptors in systemic sclerosis.

Systemic sclerosis (SSc) is a deleterious disease. Its clinical management is complicated by strong interpatient heterogeneity. Progressive organ fibrosis is linked to autoantibodies against topoisomerase 1 (TOP1). Here, we hypothesised that the interaction between anti-TOP1 autoantibodies (ATAs) and TOP1 could influence SSc pathogenesis. TOP1 is a DNA-binding enzyme. Therefore, we studied the effects and functional consequences of TOP1-DNA binding on ATA recognition. ATA monoclonal antibodies (ATA mAbs) and ATA-expressing B cell lines were generated from patient-derived TOP1-reactive B cells. Reactivity of monoclonal and polyclonal ATAs towards TOP1 and TOP1-DNA cleavage complexes (TOP1cc) was determined by enzyme-linked immunosorbent assay and mass photometry. Immunostimulatory properties of ATA mAbs in complex with TOP1/TOP1cc were assessed on monocytic THP-1 cells and primary monocytes. The stimulatory effects of TOP1-DNA complexes were tested on ATA-expressing B cells. TOP1-DNA binding differentially affected TOP1 recognition by ATA mAbs. A subset of ATA mAbs showed enhanced binding to TOP1cc, whereas others recognised TOP1 and TOP1cc to a similar extent. ATAs with enhanced TOP1cc recognition were observed in ATA+ patients and correlated with ATA levels and interstitial lung disease. These 'TOP1cc-enhanced ATAs' affected the enzymatic function of TOP1 and, in complex with TOP1cc, increased proinflammatory cytokine production by THP-1 cells and primary monocytes. B cells expressing 'TOP1cc-enhanced ATAs' responded strongly to stimulation with TOP1-DNA complexes, whereas additive effects were not observed for B cells expressing 'regular' ATAs. The differential recognition of TOP1 upon DNA binding by ATAs demonstrates heterogeneity in the ATA B cell response, possibly impacting disease-relevant processes in severe SSc.