Possible interplay between interleukin-15 and interleukin-17 into the pathogenesis of idiopathic inflammatory myopathies.

The aim of this study was to assess the serum levels of interleukin (IL)-15 and IL-17 in patients with idiopathic inflammatory myopathies (IIM) and correlate them with IL-6, IL-10, monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory protein-1α (MIP-1α), MIP-1β levels. Possible correlations with disease activity parameters were also evaluated. Sera from 14 polymyositis (PM), 10 dermatomyositis (DM), 7 anti-synthetase syndrome new onset patients and 19 healthy controls (HCs) were analyzed by multiplex immunoassay. Sera from 19 patients were analyzed after 5 months median follow-up. All patients underwent physical examination, the 5-points manual muscle test (MMT), the health assessment questionnaire and serum creatine kinase measurement. All patients received glucocorticoids, and 13 were taking also immunosuppressive therapy. At baseline, serum levels of IL-15, IL-17, MCP-1 and MIP-1β were significantly higher in IIM patients than in HCs. IL-17 serum levels were directly correlated with disease duration (r=0.39, P=0.02), while a significant inverse correlation was detected between IL-17 levels and MMT scores (r=-0.4, P=0.02). The highest IL-15 levels were present in DM patients (P=0.02 vs PM). The most striking finding was the strong correlation between IL-15 and IL-17 levels (r=0.60, P=0.0001), and this correlation was even stronger in DM patients (r=0.82, P=0.006). The strong correlation between IL-15 and IL-17 in IIM patients, and especially in DM, suggests that there may be a interplay between the two cytokines in the pathogenesis of myositis. Further studies of larger patient cohorts and muscle biopsies are needed to confirm these preliminary data.