T helper cytokines in systemic sclerosis

Abstract

Background and Objectives: Systemic sclerosis (SSc) is a chronic autoimmune disease characterized by inflammation, vasculopathy, and progressive fibrosis affecting the skin and internal organs. Immune dysregulation and endothelial dysfunction are essential players in the development of SSc. A bias toward T helper 2 (Th2) cytokines has been demonstrated to be associated with SSc, implicating SSc as a Th2-associated disease. This study aimed to investigate the role of T helper cytokines in patients with SSc and in an experimental model of SSc-associated pulmonary arterial hypertension (PAH). Methods: A total of 128 patients with SSc were recruited from the Department of Rheumatology and Clinical Immunology, University of Lübeck. 69 healthy individuals served as controls and were enrolled at the Research Center Borstel. The experimental model of SSc-PAH was induced in IL-13 transgenic (IL-13tg) mice via immunization with membrane extracts of CHO cells overexpressing human angiotensin II type 1 receptor (AT1R). To assess therapeutic potential of targeting IL-6 signaling, IL-13tg mice, either naïve or AT1R-immunized, were treated with neutralizing monoclonal antibodies (mAbs) against murine IL-6 or IL-6 receptor (IL-6R), or with corresponding isotype control antibodies. Lung pathology was evaluated by histological analysis using hematoxylin and eosin (H&E) staining. The levels of human and murine T helper cytokines were measured in serum and/or bronchoalveolar lavage (BAL) fluid using LEGENDplex™ Multi-Analyte Flow Assay Kit. Lung transcriptomes were analyzed using Agilent Mouse GE 4x44K v2 microarrays. Results: Patients with SSc exhibited significantly elevated serum levels of multiple T helper cytokines compared to healthy controls, including IL-2, IL-4, IL-6, IL-10, IFN-γ, and TNF-α. Among these cytokines, serum IL-6 levels were positively correlated with as the presence of both interstitial lung disease (ILD) and PAH. In the experimental model, treatment with anti-IL6 or anti-IL-6R did not prevent the development of experimental occlusive vasculopathy in AT1R-immunized IL-13tg mice. By contrast, a trend toward a more severe vascular pathology was observed in AT1R-immunized IL-13tg mice treated with IL-6 or IL-6R-neutralizing mAbs compared to isotype-treated controls, although the differences were not statistically significant. Furthermore, treatment with anti-IL-6 mAb alone was sufficient to induce pulmonary occlusive vasculopathy in non-immunized IL-13tg mice. Transcriptomic analysis revealed that anti-IL-6 mAb treatment dysregulated the expression of immune-related genes in the lungs of unimmunized IL-13tg mice. Conclusion: Although IL-6 has been shown to exert a proinflammatory role in many diseases, this function could not be confirmed in the present study. Moreover, my findings suggest that, in an experimental model of pulmonary vasculopathy in the context of systemic sclerosis, IL-6 may act as a protective regulator. These results provide new insights into both the pro- and anti-inflammatory roles of IL-6 in the pathogenesis of systemic sclerosis and highlight the importance of carefully reconsidering this cytokine as a potential therapeutic target for SSc-associated PAH.