Pos1276 a single cell transcriptomic analysis reveals a pro-inflammatory profile in peripheral blood cd14+ monocytes of systemic sclerosis patients

Background Systemic sclerosis (SSc) is an immune-mediated disease, which affects mostly women over 50 years old. Recently, single cell mRNA sequencing techniques (scRNA-seq) have contributed to establish the relevance of different immune cell types in SSc. However, little is known about the diversity of the peripheral blood monocytes, which play a central role in the early inflammatory response and in the maintenance of inflammation in SSc. Objectives Our aim is to analyze the composition of the peripheral blood monocyte compartment of SSc patients and to establish disease and subtype specific transcriptomic profiles at the single cell level. Methods CD14+ monocytes were isolated from peripheral blood mononuclear cells (PBMC) of 8 SSc diagnosed women and 8 age matched unaffected females. All the patients were between 50 and 70 years old and classified as either limited cutaneous SSc (lcSSc) or diffuse cutaneous SSc (dcSSc). ScRNA-seq libraries were generated using the 10x Genomics Chromium platform and the Chromium Next GEM Single Cell 5’ Reagent Kits. After QC a total of 98,543 cells remained, with an average of ~7,000 cells per sample and 36,601 detected genes. Dimensionality reduction and cell clustering were performed using Scanpy, establishing 5,000 high variable genes and 20 principal components to implement the Leiden clustering algorithm. Results We identified 11 different clusters in the SSc combined analysis of the single cell transcriptomes from both the SSc patients and the controls. Using known genes and cell markers, we identified classical monocytes, non-classical monocytes and intermediate monocytes, and a dendritic cell population (Figure 1.). Non-classical monocyte populations were under-represented in SSc patients. Overall, we observed a proinflammatory profile in SSc CD14+ monocytes, which overexpressed genes related to the interferon signaling pathways, such as IFITM2, IFITM3 or IRF1, but also S100 family genes. This proinflammatory profile is especially enriched in the activated monocyte clusters, i.e. those with high expression of S100A8/S100A9 genes. Additionally, we identified the overexpression of TMEM176A and TMEM176B in lcSSc patients compared to dcSSc patients and controls. Conclusion Our analysis of peripheral blood CD14+ monocytes in SSc patients showed an overrepresentation of non-classical monocytes and an increased interferon response compared to healthy controls. Moreover, we found subtype specific transcriptomic profiles, which suggested the possible use of monocyte subtypes as SSc biomarkers. References [1]Denton, C. P. & Khanna, D. Systemic sclerosis. Lancet 390, 1685–1699 (2017). [2]Lescoat, A., Lecureur, V. & Varga, J. Contribution of monocytes and macrophages to the pathogenesis of systemic sclerosis: recent insights and therapeutic implications. Curr. Opin. Rheumatol. 33, 463–470 (2021). [3]Matei, A.-E. et al. Biophysical phenotyping of circulating immune cells identifies a distinct monocyte-driven signature in systemic sclerosis. Arthritis Rheumatol (2022) doi:10.1002/art.42394. Acknowledgements: NIL. Disclosure of Interests None Declared.