Increased Serum Levels of the IL-33 Neutralizing sST2 in Limited Cutaneous Systemic Sclerosis

The pathophysiology of both limited cutaneous systemic sclerosis (lcSSc) and diffuse cutaneous SSc (dcSSc), representing two subtypes of an autoimmune disease of the connective tissue, is still enigmatic. Life-limiting, progressive fibrotic changes as a consequence of vasculopathy and autoimmunity are characteristic in varying extent for lcSSc and dcSSc. Previously, an increased IL-33 serum concentration in early phase SSc patients and an elevated tissue expression of its receptor, ST2L, on endothelial cells (EC) were described. While suggested as a biomarker for fibrotic diseases, for example liver fibrosis, the role of soluble ST2 (sST2) in the pathological processes and its contribution to vascular fibrosis in SSc has not been investigated. Here, we showed that sST2 is elevated in late phase limited cutaneous SSc (lcSSc) as compared to patients with shorter disease duration or with the diffuse subtype of SSc. We demonstrated that sST2, not IL-33, is significantly increased in serum of lcSSc patients with disease duration over 9 years. Soluble ST2 was not elevated in healthy controls or in SSc patients with early skin involvement or disease duration shorter than 9 years. Furthermore, we observed that sST2 serum levels were lowered by iloprost (prostacyclin) treatment. After 5 days of iloprost infusion, sST2 serum levels fell in 6 of 7 patients. Therefore, we not only like to propose sST2 as a biomarker for progressive vascular fibrosis, but moreover, suggest that the involvement of sST2 in the pathogenesis of lcSSc may be exploited therapeutically.