ARTHRITIS & RHEUMATISM Vol. 58, No. 7, July 2008, pp 2163–2173 DOI 10.1002/art.23486 © 2008, American College of Rheumatology Induction of Interferon- by Scleroderma Sera Containing Autoantibodies to Topoisomerase I Association of Higher Interferon- Activity With Lung Fibrosis Daniel Kim, 1 Anders Peck, 1 Deanna Santer, 1 Prashant Patole, 1 Stephen M. Schwartz, 1 Jerry A. Molitor, 2 Frank C. Arnett, 3 and Keith B. Elkon 1 Objective. Peripheral blood cells (PBMCs) from some patients with systemic sclerosis (SSc) express an interferon- (IFN) signature. The aim of this study was to determine whether SSc patient sera could induce IFN and whether IFN 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 experi- ments, different cell extracts or inhibitors of plasmacy- toid dendritic cell (DC) activation, Fc receptor II (FcRII), endocytosis, or nucleases were used. IFN was measured by enzyme-linked immunosorbent assay. Results. Topo I–containing sera induced signifi- cantly higher levels of IFN as compared with all other groups. IFN induction was inhibited by anti–blood dendritic cell antigen 2 (90%), anti-CD32 (76%), bafilo- mycin (99%), and RNase (82%). In contrast, ACAs induced low levels of IFN even when necrotic, apopto- tic, or demethylated extracts were used, despite the fact that CENP-B–binding oligonucleotide containing 2 CpG motifs effectively stimulated IFN. IFN 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 and may explain the IFN signature observed in SSc. IFN is induced by plasma- cytoid DCs and required uptake of immune complexes through FcRII, endosomal transport, and the presence of RNA, presumably for interaction with Toll-like recep- tor 7. The higher IFN 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 IFN may contribute to tissue injury. Systemic sclerosis (SSc) is a complex auto- immune disease characterized by inflammation, immune activation, excessive extracellular matrix deposition, fi- brosis, and vascular obliteration in the skin and internal organs. SSc can be divided into 2 major subsets, limited cutaneous SSc (lcSSc) and diffuse cutaneous SSc (dc- SSc), according to the extent to which the skin is affected. The lcSSc form is defined by the presence of skin thickening in areas solely distal to the elbows and knees, with or without involvement of the face. Patients with lcSSc present with various clinical features of CREST syndrome (calcinosis, Raynaud’s phenomenon, Mr. Peck’s work was supported by a University of Washington Medical Student grant. Drs. Schwartz, Molitor, and Elkon’s work was supported by the Scleroderma Research Foundation; Dr. Elkon’s work was also supported by the Dana Foundation. Dr. Arnett’s work was supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases, Center of Research Translation in Scleroderma (grant 5-P50-AR-054144) and the National Center for Research Resources, Clinical and Translational Science Award (grant 1-U54- RR-23417), NIH. The Scleroderma Family Registry and DNA Repos- itory were supported in part by the Joanna F. von Behringer Founda- tion and the Hayward Family Foundation. 1 Daniel Kim, BS, Anders Peck, BS, Deanna Santer, BS, Prashant Patole, PhD, Stephen M. Schwartz, MD, PhD, Keith B. Elkon, MD: University of Washington, Seattle; 2 Jerry Molitor, MD, PhD: Virginia Mason Hospital, Seattle, Washington; 3 Frank C. Arnett, MD: University of Texas Health Science Center at Houston. Address correspondence and reprint requests to Keith B. Elkon, MD, University of Washington, Division of Rheumatology, 1959 NE Pacific Avenue, Box 356428, Seattle, WA 98195. E-mail: elkon@u.washington.edu. Submitted for publication October 17, 2007; accepted in revised form March 5, 2008. 2163