Salivary Galectin-9 Levels in Primary Sjögren's Disease: An Observational Cross-Sectional Case-Control Study

Background/Objectives: Primary Sjögren's disease is a systemic autoimmune disease characterized by chronic inflammation of exocrine glands and heterogeneous clinical manifestations. There remains a need for objective, non-invasive biomarkers that reflect local glandular involvement and disease-related immune activity. Methods: This observational cross-sectional case-control study included 34 patients fulfilling the 2016 ACR/EULAR classification criteria for primary Sjögren's disease and 34 healthy controls between December 2024 and February 2025. Unstimulated whole-saliva samples were collected in the morning using the passive drool method, and salivary galectin-9 concentrations were measured via the enzyme-linked immunosorbent assay. Disease activity and symptom burden were assessed using validated indices, and receiver operating characteristic analysis was performed to evaluate discriminatory performance. Results: Salivary galectin-9 levels were significantly higher in patients with primary Sjögren's disease compared with healthy controls. However, no significant associations were observed between salivary galectin-9 levels and disease activity scores after correction for multiple comparisons, nor with patient-reported symptoms, autoantibody profiles, Schirmer test results, or minor salivary gland biopsy findings. Salivary galectin-9 demonstrated limited discriminative ability between patients and controls. Conclusions: Salivary galectin-9 levels were elevated in primary Sjögren's disease and may be associated with local glandular immune processes. Further prospective studies are needed to determine their clinical relevance.