Activated IL-22 pathway occurs in the muscle tissues of patients with polymyositis or dermatomyositis and is correlated with disease activity.

OBJECTIVE: The aim of this study was to assess the expression of IL-22, IL-22 receptor 1 (IL-22R1), IL-22 binding protein (IL-22BP) and p-STAT3 in muscle tissue from patients with PM and DM. METHODS: Levels of IL-22, IL-22R1, IL-22BP and STAT3 mRNA were quantified by RT-PCR. The expression of IL-22, IL-22R1, IL-22BP and p-STAT3 was also analysed using immunohistochemistry. RESULTS: Significant modulation of the IL-22 pathway was observed in inflammatory myopathic tissues. In particular, a significant overexpression of IL-22 at the protein but not the mRNA level was observed in PM/DM tissues and was correlated with myositis activity. IL-22R1 aberrant expression was also observed among infiltrating mononuclear cells and necrotic muscle cells. IL-22BP, which inhibits IL-22 signalling, was expressed only in some muscle fibres in PM/DM patients. CONCLUSION: Our findings indicate that the IL-22 pathway is activated in inflammatory myopathic tissues and may be involved in the induction of muscle inflammatory processes and muscle necrosis.