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.