Expression of interleukin-17 in primary Sjögren's syndrome and the correlation with disease severity: A systematic review and meta-analysis.

The aberrant expression of interleukin-17 (IL-17) has been reported in primary Sjögren's syndrome (pSS). Abnormalities in IL-17 can promote the production of pro-inflammatory cytokines and aggravate autoimmune disorders. The aim of this study was to investigate alterations of IL-17 in patients with pSS and explore the correlation between IL-17 and disease severity. Eight databases were searched for original studies reporting the expression of IL-17 in patients with pSS and controls. Eligible reports were included in the pooled analysis, and subgroup evaluations were performed according to different types of controls and IL-17 measurement methods. Newcastle-Ottawa Scale criteria were used to assess the risk of bias of the included studies. In total, 45 articles are included in the meta-analysis. The expression of IL-17 is significantly increased in patients with pSS compared to controls. Furthermore, patients with pSS without immunosuppressive treatment show markedly higher IL-17 levels. In addition, patients with pSS with positive rheumatoid factors tend to express a higher level of IL-17 than patients with negative rheumatoid factors. Negative correlations between IL-17 levels and ocular parameters are also found in patients with pSS. The results are similar after adjustment by "trim and fill" methods. In conclusion, the expression of IL-17 is obviously increased in patients with pSS, especially among those without immunosuppressive treatment. In addition, IL-17 level correlates with the disease severity of pSS. These findings demonstrate the significance of IL-17 overexpression in patients with pSS and may provide insights for the development of therapeutic interventions targeting IL-17 for pSS.