Resolving Resident Colonic Muscularis Macrophage Diversity and Plasticity During Colitis

Background: Immune cell populations within the intestinal muscularis propria are poorly resolved during colitis. Maintaining homeostasis in this unique niche is of critical importance, highlighted by the poorer prognosis of inflammatory bowel disease associated with inflammation in the muscularis propria. Methods: This study utilizes single-cell RNA sequencing to survey the immune cell populations within the muscularis propria of normal colon and DSS-induced colitis. Results: In naïve conditions, transcriptional duality is observed in MMφ with two major supopulations: conventional resident Cx3cr1+ MMφs and Lyve1+ MMφs. During colitis, significant changes occur within the muscularis propria, with increases in B-cells, T-cells, monocytes, neutrophils, and dendritic cells. Unlike in the mucosa, single cell transcriptomics indicates that resident MMφs are retained during colitis and exhibit plasticity toward an inflammatory profile. Lyve1+ MMφs, which express anti-inflammatory marker CD163, are absent during colitis. In contrast, resident Cx3cr1+ MMφs remain during colitis. Conclusions: Our findings provide a resource for understanding the immune system in the muscularis propria niche during colitis and resolve the heterogeneity and origins of proinflammatory MMφs during colitis by demonstrating the plasticity of the persistent MMφ population.