DOP04 Single cell RNA sequencing reveals a potential role for IFNγ in priming circulating monocytes for intestinal inflammatory function in Crohn’s Disease.
Hornsby, E.(1)*;Gadhok, R.(1);Yadon, A.N.(2);Lindsay, J.O.(1);Stagg, A.J.(1);
(1)Queen Mary University of London, Blizard Institute, London, United Kingdom;(2)Gilead Sciences- Inc, 199 East Blaine Street, Seattle, United States;
Background
Hyper-inflammatory monocyte-derived cells accumulate in the intestine and contribute to pathology in inflammatory bowel disease (IBD). Our previous work has shown that intestinal monocyte-derived cells from Crohn's Disease patients have a reduced response to the immunoregulatory cytokine IL-10 and that this property is already established in circulating monocytes prior to their arrival in the intestine. Here, we have used scRNAseq and functional experiments to define the scope of IBD-associated changes in blood monocytes and explore the role of inflammatory cytokines in shaping these.
Methods
Total monocytes were isolated from the peripheral blood of 12 newly diagnosed, treatment naive IBD patients with active endoscopic disease (6 Crohn’s Disease [CD] and 6 Ulcerative Colitis [UC]) and 10 healthy controls (HC) by negative magnetic selection. scRNAseq was performed using the 10x Genomics Chromium 3’ assay at a target capture rate of 1000 cells/sample and sequencing at ~50,000 reads/cell. Data were analysed using Cell Ranger, Seurat, Metascape and Gene Set Enrichment Analysis. Blood CD14+ monocytes from healthy donors were pre-incubated in medium alone or with IFNγ (100U/ml) for 24 hours. Inhibition of LPS-induced TNFα production by IL-10 was measured by intracellular cytokine staining and flow cytometry.
Results
UMAP clustering identified six transcriptionally distinct monocyte clusters: clusters 0, 1 and 2 mapped to classical monocytes; cluster 3 to non-classical monocytes; cluster 4 to intermediate monocytes; and cluster 5 contained platelet signals. The proportion of cluster 4 was increased in CD patients compared to HC. Differential gene expression analysis of CD and UC monocyte clusters compared to healthy controls identified a total of 246 differentially expressed genes (DEGs) in CD and 149 in UC. Only 39 of these DEGs were significantly affected in both diseases. Both CD and UC DEGs were significantly enriched for pathways related to cytokine signalling and inflammation (Figure 1).
IFNγ and TNFα -response gene sets were positively enriched in CD, but negatively enriched in UC (Figure 2). 
Pre-treatment of healthy monocytes with IFNγ in vitro reduced their response to IL-10 as measured by inhibition of LPS-induced TNFα (Figure 3).
Conclusion
Expression of genes associated with inflammation and cytokine signaling are altered in blood monocytes from IBD patients implying their modification by systemic signals prior to arrival in the intestinal mucosa. Cytokine- (IFNγ and TNFα) stimulated genes are differentially affected in CD and UC monocytes. In CD, systemic IFNγ may reduce the responsiveness of monocytes to IL-10 to prime them for inflammatory function.