Increased expression of CXCL10 and CCL3 salivary gland chemokines in primary Sjögren’s syndrome detected and systematically quantified using RNAscope®<i>in situ</i> hybridization

Primary Sjögren's syndrome is a chronic inflammatory disease characterized by the destruction of exocrine glands. We have previously shown significantly upregulated levels of CXCL10 and CCL3 chemokines in saliva from Sjögren's syndrome patients. In this study, we examined the expression pattern and localization of these chemokines at the site of inflammation in patients' minor salivary glands using novel RNAscope® in situ hybridization. Minor salivary glands from 33 primary Sjögren's syndrome patients and 22 non-Sjögren's syndrome (non-SS) sicca controls were included. The biopsies were formalin-fixed, paraffin-embedded, and histopathologically evaluated. The CXCL10 and CCL3 mRNA expression in the glandular tissue was investigated using reverse transcription quantitative real-time polymerase chain reaction followed by an RNAscope® in situ hybridization. The mRNA expression of CXCL10 was higher than CCL3 in all patients. Significantly elevated expression of CXCL10 and CCL3 was detected in patients that also expressed autoantibody positivity and a positive biopsy for mononuclear cell infiltrates when compared with non-SS sicca controls. CXCL10 was localized as clusters within focal infiltrates as well as adjacent to acinar and ductal epithelium, while CCL3 was expressed as scattered single mRNA molecules in focal infiltrates and in acinar cells. Our findings suggest CXCL10 as a possible disease biomarker in primary Sjögren's syndrome due to its upregulated expression in both saliva and minor salivary glands of patients and the localization in the tissue. This should be re-assessed in a larger primary Sjögren's syndrome patient cohort, followed by additional functional studies to further validate its potential as a disease biomarker.