Induction of interferon-α by scleroderma sera containing autoantibodies to topoisomerase I

Objective. Peripheral blood cells (PBMCs) from some patients with systemic sclerosis (SSc) express an interferon-alpha (IFN alpha) signature. The aim of this study was to determine whether SSc patient sera could induce IFNa and whether IFN alpha induction was associated with specific autoantibodies and/or clinical features of the disease. Methods. SSc sera containing autoantibodies against either topoisomerase I (anti-topo I; n = 12), nucleolar protein (ANoA; n = 12), or centromeric protein (ACA; n = 13) were cultured with a HeLa nuclear extract and normal PBMCs. In some experiments, different cell extracts or inhibitors of plasmacytoid dendritic cell (DC) activation, Fc gamma receptor II (Fc gamma RII), endocytosis, or nucleases were used. IFN alpha was measured by enzyme-linked immunosorbent assay. Results. Topo I-containing sera induced significantly higher levels of IFN alpha as compared with all other groups. IFN alpha induction was inhibited by anti-blood dendritic cell antigen 2 (90%), anti-CD32 (76%), bafilomycin (99%), and RNase (82%). In contrast, ACAs induced low levels of IFN alpha even when necrotic, apoptotic, or demethylated extracts were used, despite the fact that CENP-B-binding oligonucleotide containing 2 CpG motifs effectively stimulated IFN alpha. IFN alpha production was significantly higher in patients with diffuse SSc (mean +/- SEM 641 +/- 174 pg/ml) than in those with limited SSc (215 +/- 66 pg/ml) as well as in patients with lung fibrosis than in those without. Conclusion. Autoantibody subsets in SSc sera differentially induce IFN alpha and may explain the IFN alpha signature observed in SSc. IFN alpha is induced by plasmacytoid DCs and required uptake of immune complexes through Fc gamma RII, endosomal transport, and the presence of RNA, presumably for interaction with Toll-like receptor 7. The higher IFN alpha induction in sera from patients with diffuse SSc than in those with limited SSc as well as in sera from patients with lung fibrosis suggests that IFNa may contribute to tissue injury.