Background/Purpose: Primary Sjögren’s Syndrome (pSS) shares with SLE and RA features including their predominance in women, immunological characteristics and genetic risk background. Hence, to dissect the heterogeneity across these IMIDs is key to design precision medicine strategies. Single cell transcriptomics allows to interrogate patients’ samples at great resolution to inform on common and specific pathogenic molecular mechanisms that drive disease. This is relevant not only for the discovery of potentially actionable targets, but also to identify patients likely to benefit from such novel therapeutic interventions. Despite pathogenic mechanisms can be organ-specific, immune cells are mobilized via peripheral blood initiating inflammatory responses. In that respect, the profiling of peripheral blood mononuclear cells (PBMCs) is important since PBMCs may show cell-type signatures that can define disease specific pathogenesis, with the advantage of being an easily accessible tissue.

Methods: PBMCs from 8 pSS and 5 healthy donors (H)  were isolated in Ficoll gradient, and processed with Chromium Single Cell 3’ kit v3 (10X Genomics). A median of 8,008 cells per sample were profiled. Raw sequences were demultiplexed and mapped against the genome using Cell Ranger. Downstream analyses, including QC filtering, normalization, and integration were done with Seurat. Immune cell were automatically annotated using Azimuth. Single cell data from 6 RA patients (71,224 cells) and 8 SLE patients (71,224 cells), was obtained from the DoCTIS Consortium project.

Results: Differential cell abundance analysis of PBMCs among the 4 groups (H, pSS, SLE and RA) showed a significant increment in the CD8 lymphocyte population with CD8TEM features, that is specific to pSS. In turn, lower numbers of CD8 naïve T cells were observed in pSS compared to healthy individuals, a change also found in RA but not in SLE. Gene expression analysis revealed that CD14+ monocytes show the highest number of differentially expressed genes (DEGs) in pSS compared to controls. Analysis of these DEGs in CD14+ monocytes from SLE and RA patients showed a significant antagonism, with many genes showing a differential expression in the opposite direction. Second to monocytes, CD4TCM lymphocytes showed also a large number of significant DEGs between pSS patients and controls, but no significant antagonism was found in CD4TCM from RA or SLE. Pathway analysis of the genes exclusive to pSS (i.e. differentially expressed in pSS but not in SLE or RA), identified an association with the regulation of type I interferon and tumor necrosis factor production. Among the former, the family of genes encoding 2′–5′ oligoadenylate synthetases (OAS1 to OAS3) were found to be significantly overexpressed in CD14+ monocytes. OAS1 is a well-known risk gene for pSS associated at a genome-wide level.

Conclusion: We have mapped PBMCs from pSS and compared it with HC as well as SLE and RA, covering a total of 241,841 cells, providing a valuable resource for further in depth analysis. Our study reveals relevant disorder and cell-specific transcriptomic changes such as the upregulation of OAS family of IFNI response genes in CD14+ monocytes providing further clues into the mechanisms driving the disease.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/single-cell-rna-seq-characterization-of-circulating-immune-cells-in-sjogrens-syndrome-comparison-to-sle-and-rheumatoid-arhtritis/