Systemic sclerosis (SSc) is a chronic multisystem disorder characterized by fibrosis and autoimmunity. Interleukin (IL)-31 has been implicated in fibrosis and T helper (Th) 2 immune responses, both of which are characteristics of SSc. The exact role of IL-31 in SSc pathogenesis is unclear. Here we show the overexpression of IL-31 and IL-31 receptor A (IL-31RA) in dermal fibroblasts (DFs) from SSc patients. We elucidate the dual role of IL-31 in SSc, where IL-31 directly promotes collagen production in DFs and indirectly enhances Th2 immune responses by increasing pro-Th2 cytokine expression in DFs. Furthermore, blockade of IL-31 with anti-IL-31RA antibody significantly ameliorates fibrosis and Th2 polarization in a mouse model of SSc. Therefore, in addition to defining IL-31 as a mediator of fibrosis and Th2 immune responses in SSc, our study provides a rationale for targeting the IL-31/IL-31RA axis in the treatment of SSc.

Objective: To determine the function and serum levels of soluble forms of programmed death 1 (sPD‐1) and one of its ligands, soluble PD ligand 2 (sPD‐L2), in patients with systemic sclerosis (SSc) and in a mouse model of topoisomerase I (topo I)–induced SSc.Methods: Serum levels of sPD‐1 and sPD‐L2 in 91 patients with SSc were examined by enzyme‐linked immunosorbent assay (ELISA). Expression of PD‐1 and PD‐L2 on T cells, B cells, and macrophages was quantified by flow cytometry. The effects of blockade of PD‐1 and PD‐L2 were analyzed by microfluidic ELISA (micro‐ELISA), a technique that can measure very low amounts of cytokines. In addition, the effects of sPD‐1 and sPD‐L2 on disease progression were assessed in mice with topo I–induced SSc.Results: Serum levels of sPD‐1 and sPD‐L2 were elevated in patients with SSc and correlated with the extent of fibrosis and immunologic abnormalities. Expression levels of PD‐1 and PD‐L2 were significantly elevated on SSc T cells, B cells, and macrophages. Micro‐ELISA analysis of serum samples from patients with SSc showed that PD‐L2^high B cells had higher levels of interleukin‐10 (IL‐10) production compared with PD‐L2^low B cells, indicating that PD‐L2 acts as a regulator of T cell cytokine production via cognate interactions with T cells and B cells. In mice with topo I–induced SSc, production of IL‐10 by topo I–specific B cells in cultures with T cells and topo I protein was significantly higher than that by conventional B cells, and intraperitoneal injection of recombinant chimeric PD‐1‐Fc and PD‐L2‐Fc canceled these enhanced effects.Conclusion: These results suggest that sPD‐1 and sPD‐L2 contribute to disease development in SSc via the regulation of cognate interactions with T cells and B cells.