OBJECTIVES: Serum soluble CD25 (sCD25) is associated with T cell activation and regarded as a marker of disease activity in autoimmune disorders. The purpose of our study was to investigate the clinical relevance of sCD25 in patients with primary Sjögren's syndrome (pSS). METHODS: Sixty-five pSS patients and 60 healthy controls (HCs) with comparable age and gender were recruited. Serum samples were collected and sCD25 concentrations were measured using enzyme-linked immunosorbent assay (ELISA). Clinical and laboratory changes were examined after 12 weeks of treatment, and data were recorded in detail. The European League Against Rheumatism Sjögren's syndrome disease activity index (ESSDAI) was used to evaluate disease activity. RESULTS: Serum sCD25 levels were significantly increased in pSS patients, compared to HCs (p<0.001). The increased sCD25 were positively associated with ESSDAI scores (p=0.006), especially the haematological domain (p=0.002), and erythrocyte sedimentation rate, and levels of C-reactive protein, immunoglobulin G and γ-globulin (p<0.001, <0.001, 0.045 and 0.011, respectively). High sCD25 was strongly associated with anaemia (p=0.014) and was inversely correlated with haemoglobin levels (p=0.002). In further analysis, we found that patients with autoimmune haemolytic anaemia (AIHA) had the highest levels of sCD25, followed by patients with chronic disease of anaemia (ACD) and iron-deficiency anaemia (IDA). With the improvement after treatment, serum sCD25 levels were significantly decreased, accompanied by resolved anaemia compared to baseline (p=0.001). CONCLUSIONS: sCD25 was associated with disease severity, especially anaemia in patients with pSS and may serve as an indicator of disease activity.
