Relationships between increased circulating YKL-40, IL-6 and TNF-α levels and phenotypes and disease activity of primary Sjögren's syndrome

•Serum levels of YKL-40, IL-6 and TNF-α were increased in pSS patients.•YKL-40, IL-6 and TNF-α were mainly involved in systemic inflammation of pSS.•Each of YKL-40, IL-6 and TNF-α had separate association with distinct pSS phenotype. There is now no single score or marker useful for evaluating disease activity of primary Sjögren's syndrome (pSS). This study was designed to explore the associations of circulating YKL-40, interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) with systemic activity and phenotypes of pSS. This study included 58 pSS patients and 30 healthy controls (HC). The sera were measured by multiplex immunoassay for YKL-40, IL-6 and TNF-α concentrations. The disease activity of pSS patients was evaluated by European league against rheumatism (EULAR) SS disease activity index (ESSDAI). Local severity was assessed in accordance with the Tarpley score. Serum YKL-40, IL-6 and TNF-α levels significantly elevated in pSS patients compared with those in HC (all P