Serum level of soluble CX3CL1/fractalkine is elevated in patients with polymyositis and dermatomyositis, which is correlated with disease activity

Expressions of CX3CL1 and CX3CR1 in muscle and lung tissue were analyzed by immunohistochemistry. Serum CX3CL1 concentrations were measured by ELISA. For evaluation of patients' disease activity, serum creatinine kinase, manual muscle testing, and the alveolar-arterial oxygen pressure difference were used independently.CX3CL1 was expressed on infiltrated mononuclear cells and endothelial cells in muscle affected by PM and DM and in lung with ILD, whereas CX3CR1 was expressed on some CD4+ T cells, a majority of CD8+ T cells, and most macrophages in muscle, and on infiltrated mononuclear cells in the lung. Serum soluble CX3CL1 was significantly higher in PM patients and DM patients than in healthy controls. The CX3CL1 level was correlated with serum creatinine kinase and manual muscle testing score. In patients with PM and DM with ILD, serum CX3CL1 was also correlated with alveolar-arterial oxygen pressure difference. Furthermore, CX3CL1 was significantly decreased after conventional treatment.The interaction between CX3CL1 and CX3CR1 might contribute to the inflammatory cell infiltration into affected muscle and lung with ILD in PM patients and DM patients. Serum CX3CL1 level could be a surrogate marker of disease activity.Polymyositis (PM) and dermatomyositis (DM) are chronic inflammatory diseases affecting skeletal muscle with infiltration of mononuclear cells, such as CD4 and CD8 T cells and macrophages [1]. The infiltrating cells might contribute to the pathogenesis of PM and DM by releasing cytokines and cytotoxic molecules, such as TNF, perforin, and granzyme [2,3].Patients with PM and patients with DM commonly show proximal muscle weakness, and some patients exhibit complication of interstitial lung disease (ILD), which may be associated with rapidly progressive respiratory insufficiency leading to death [4,5]. Serum creatinine kinase (CK) is helpful in evaluating both myositis activity and its response to the treatment. In some patients, however, serum levels