Background/Purpose: Salivary gland (SG) dysfunction is commonly associated with the autoimmune disease primary Sjögren’s syndrome (pSS). Whilst the more advanced stages of the disease are well studied, the earliest events triggering SG dysfunction remain enigmatic. We sought to elucidate the earliest events suggestive of SG dysfunction, using a non-biased single cell sequencing cell-interaction approach, and biopsies of the parotid SG.

Methods: Parotid gland biopsies were harvested from 12 SSA⁺ pSS patients grouped into those with with no infiltration (focus score (FS) =0, n=4), intermediate infiltration (FS 0-1, n=4) and a positive focus score (FS >1, n=4). Healthy parotid glands were also harvested (n=4). After digestion, single cell RNA sequencing was performed on all cells present in all biopsies. A total of 24,817 cells were sequenced. Every droplet with ≥500 UMIs was considered a cell. Cells with < 200 expressed genes were discarded, as were cells showing mitochondrial gene expression as >25% of total genes. Data was normalized and scaled in SCTransform, and Seurat and CellChat platforms used for further analysis.

Results: 24 broad cell types were identified in the total sequenced cells, broadly grouped into acinar cells, ductal cells, tissue macrophages and monocytes, B cells, T cells, plasma cells and fibroblasts. CellChat analysis suggested in FS=0 pSS group that there may be communication between fibroblasts and subsets of the T, B and monocytes. This hypothesized communication was absent or minimal in healthy control, pSS FS0-1 and pSS FS >1 groups. Further pathway analysis pinpointed CXCL12 ligand expression by fibroblasts and CXCR4 receptor by T and B cells and monocytes, in additional to the MIF pathway, as potentially active signaling pathways between the cell types.

In order to validate the immunogenic role of fibroblasts early in SG damage in pSS, we are in the process of establishing fibroblast cultures from FS=0 biopsies of pSS patients and comparing their transcriptomes, immunomodulatory capabilities and effect when co-cultured with T cells, B cells and saliva producing acinar cells.

Conclusion: Theoretical analysis based on single cell sequencing data would imply that fibroblast may occupy a central role in the initiation of SG dysfunction or damage in pSS patients. Further validation of this may help us understand how to target this early disease stage, and minimize gland dysfunction.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/single-cell-rna-sequencing-points-to-a-role-for-fibroblasts-early-in-salivary-gland-dysfunction-in-primary-sjogrens-syndrome/