Increased expression of CXCL10 and CCL3 salivary gland chemokines in primary Sjögren's syndrome detected and systematically quantified using novel RNAscope® in situ hybridisation.

Primary Sjogren's syndrome is a chronic inflammatory disease characterised by the destruction of exocrine glands. We have previously shown significantly upregulated levels of CXCL10 and CCL3 chemokines in saliva from Sjogren's syndrome patients. In this study, we examined the expression pattern and localisation of these chemokines at the site of inflammation in patients' minor salivary glands using novel RNAscope® in situ hybridisation. Minor salivary glands from 33 primary Sjogren's syndrome patients and 22 non-Sjogren's syndrome 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 RNAscope® in situ hybridisation. 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 to controls. CXCL10 was localised 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 Sjogren's syndrome due to its upregulated expression in both saliva and minor salivary glands of patients and the localisation in the tissue. This should be re-assessed in a larger primary Sjogren's syndrome patient cohort, followed by additional functional studies to further validate its potential as a disease biomarker.