Background/Purpose: Salivary gland biopsy is essential in primary Sjögren’s syndrome (pSS) diagnostics. However, tissue analysis using the traditional method has several limitations including inaccuracy of quantification of lymphocytic infiltration and poor correlation with dryness. To perform biomarker identification in the target organ, tissue would have to be sacrificed. By performing saliva proteomics the biopsy tissue can be saved, but this technique has not yielded consistent biomarkers and is limited by the absence of saliva production in many sicca patients. We explored whether Luminex analysis of a multitude of cytokines in salivary gland secretomes could provide biomarkers to stratify sicca patients and insights in pathogenesis.

Methods: Labial salivary gland (LSG) tissues were rinsed after biopsy and incubated in 200µL of saline for 1h at room temperature. Tissue supernatants were rendered cell-free, frozen in liquid nitrogen and stored at -80°C. Hundred and four soluble mediators were measured in supernatants from pSS and non-Sjögren’s sicca (nSS) patients by Luminex. Tissue supernatants from 8 pSS and 8 nSS patients were selected for analysis based on matched biopsy weights. Findings from this discovery cohort were validated in an additional cohort (n=34 nSS, 26 pSS) and correlations with clinical parameters were assessed. 

Results: Levels of 20 cytokines were significantly different between the nSS and pSS patients in the discovery cohort (all at least p<0.05). These 20 and 13 additional cytokines based on a trend towards statistical significance (p<0.10) were measured in an additional cohort. Weights of the biopsies did not significantly differ between the groups (65.9±8.0mg versus 66.5±5.5mg). Fifteen out of the 20 significantly different cytokines were validated and an additional 7 cytokines were significantly elevated in pSS as compared to nSS patients without autoimmune features (including IL-21, IFN-γ, CXCL10, CXCL13 and sIL-7R, all p<0.05). Interestingly, CXCL10 and MIP-3β were also significantly elevated in nSS patients with signs of autoimmunity (eg. CXCL10 nSS: 0.9±0.5pg/mL, nSS with LFS>0 and/or anti-SSA: 7.8±4.4pg/mL, pSS 41.0±21.0pg/mL). In pSS patients numerous cytokines strongly correlated with each other and significantly correlated with lymphocytic focus scores, serum IgG levels and interestingly Schirmer’s tests (n=11, 23 and 3, respectively). Additionally, various cytokines were associated with autoimmunity including elevation in anti-SSA+ versus anti-SSA- patients (n=11, all at least p<0.05). 

Conclusion: Reproducible detection of aberrant cytokine expression in LSG secretomes seems a valuable novel tool to unravel cytokine networks correlating with clinical parameters in sicca patients. This new method represents a helpful aid to provide insights in pSS immunopathology and to identify therapeutic targets and biomarkers for diagnosis, prognosis and treatment response.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/salivary-gland-secretome-a-novel-tool-to-identify-biomarkers-of-dryness-and-immunopathology-in-primary-sjogrens-syndrome-and-non-autoimmune-sicca-patients/