The role of interleukin (IL)-17 in anxiety and depression of patients with rheumatoid arthritis

Background: Pro-inflammatory cytokines are found to be elevated in patients with anxiety and depression but whether their serum levels are related to anxiety and depression is unknown. We used rheumatoid arthritis (RA) as an inflammatory disease model to explore such relationships. Methods: Eighteen RA patients and 18 healthy controls matched for age and gender were assessed for the severity of anxiety and depression with the hospital anxiety and depression scale (HADS). Disease activity of RA and pain were assessed by the Disease Activity Scale (DAS-2) 8 and visual analogue scale of pain, respectively. Serum pro-inflammatory cytokine levels, including tumor necrosis factor (TNF)-alpha, interleukin (IL)-6 and IL-17 were determined by enzyme-linked immunosorbant assay. The differences in cytokine levels between RA patients and healthy controls, as well as within the RA group with and without anxiety and depression, were compared by using the Mann-Whitney U-test. The correlations between anxiety, depression and pro-inflammatory cytokines were explored by Spearman's rank correlation. Multiple linear regression was used to adjust for DAS-28 and pain. Results: Serum TNF-alpha, IL-6 and IL-17 levels were significantly higher in RA patients than those of healthy subjects (P < 0.001, P = 0.012 and P = 0.016, respectively). Within the RA group, serum IL-17 level was significantly higher in those with anxiety than those without (P = 0.044). Additionally, IL-17 level was positively correlated with the severity of anxiety, even after adjustment for DAS-28 and pain. Conclusion: Serum IL-17 was elevated in RA patients, especially in those with anxiety. In addition, IL-17 level was independently associated with higher anxiety score.