Correlation between salivary cystatin D level and salivary gland injury in patients with primary Sjögren syndrome

Objective To investigate the correlation between salivary cystatin D level and salivary gland injury in patients with primary Sjögren syndrome (pSS). Methods A total of 51 pSS patients admitted in the Department of Rheumatology and Immunology of the First Affiliated Hospital of Xi'an Jiaotong University from September 1, 2022 to June 30, 2023, and 51 age- and gender-matched healthy individuals who took physical examination in the hospital during same period were enrolled in the study. The level of salivary cystatin D was detected, and the difference in the level between the 2 groups was compared using an independent-samples t test. Pearson correlation analysis was applied to analyze the correlation between salivary cystatin D and clinical parameters in the patients. Results The pSS patients had significantly lower cystatin D level than the healthy controls (206.55±108.11 vs 374.32±172.24 pg/mL, P < 0.01). The cystatin D level in the pSS patients was positively correlated with both static (r=0.433, P=0.002) and dynamic salivary flow rates (r=0.363, P=0.009). The patients with higher score of salivary gland ultrasonography (SGUS) had obviously lower cystatin D than those with lower SGUS score (parotid gland: 160.75±85.56 vs 290.53±95.17 pg/mL, P < 0.01; submandibular gland: 157.76±87.59 vs 276.25±97.06 pg/mL, P < 0.01). The cystatin D level was also negatively correlated with peripheral blood IL-6 level (r=-0.453, P=0.001) and CD4+ T cell count (r=-0.396, P=0.005) in the pSS patients. Conclusion Salivary cystatin D level can be used as an indicator of salivary gland damage for pSS patients.