Diagnostic value of aquaporin 1 and 5 antibodies in primary Sjögren's syndrome

Objective To explore the diagnostic value and clinical relevance of antibodies against aquaporin-1 (anti-AQP1) and aquaporin-5 (anti-AQP5) in primary Sjögren's syndrome (pSS), and investigate new potential biomarkers that can contribute to the diagnosis. Methods A prospective cohort trial was conducted on 70 patients with pSS (pSS group), 67 patients with other connective tissue diseases and 39 healthy individuals admitted to Department of Rheumatology and Immunology of our hospital from September 2021 to March 2022. The patients with other connective tissue diseases and healthy individuals were assigned into the control group. The contents of anti-AQP1 and anti-AQP5 were measured by enzyme linked immunosorbent assay (ELISA). Meanwhile, EULAR Sjögren's syndrome disease activity index (ESSDAI) score, and levels of anti-nuclear antibody, anti-SSA antibody, anti-SSB antibody, anti-Ro52 antibody, ds- DNA, rheumatoid factor and fodrin were collected and analyzed with Chi-square test for correlation. Results No statistical difference was observed in the level of anti-AQP1 between the pSS group and control group (P>0.05), but the level of anti-AQP5 was significantly higher in the pSS group than the control group [26.41 (24.05, 28.08) vs 7.63 (5.49, 10.29) ng/mL, P < 0.05]. ROC curve analysis showed that the area under the curve of anti-AQP1 was 0.523 (P>0.05), with a sensitivity of 0.371 and a specificity of 0.726. While, the area under the curve of anti-AQP5 was 0.915 (P < 0.05), with a sensitivity of 0.957 and a specificity of 0.821. The anti-AQP5 level was positively correlated with the levels of anti-SSA antibody, anti-SSB antibody, anti-Ro52 antibody, anti-nuclear antibody and rheumatoid factor (P < 0.05), but had no correlation with ESSDAI score in the pSS patients (P>0.05). Conclusion The serum level of anti-AQP5 is significantly increased in pSS patients, with a sensitivity of 95.7% and a specificity of 82.1%, and is associated with clinical practice and of high potential diagnostic value.