Relevance of mouse and human IBD patients-derived colon organoids to investigate intestinal macrophage differentiation

The gastrointestinal tract is a remarkable example of complex biology, with a constant dia-logue between the intestinal epithelium, in close contact with the microbiota, and the im-mune cells that protect the gut from infection. Organoids have revolutionized our approach to modelling the intestinal cellular compartment and have opened new avenues for unravel-ling the mechanisms involved in intestinal homeostasis and chronic pathogenesis such as inflammatory bowel disease. To date, few models have been established to explore the role of the colon, which is however the main site of inflammation in ulcerative colitis (UC). Here, we used conditioned media produced by colon organoids (OCM) from mice or human (con-trol and UC patients) to investigate the relationship between macrophages and the colon epi-thelium. We addressed transcriptomic profiles of OCM-stimulated bone marrow-derived macrophages and found that these cells exhibited a unique anti-inflammatory signature dis-tinct from that of conventional in vitro IL-4/IL-13 M2 differentiated macrophages. In addi-tion, OCM induced a clear CD5 antigen-like-mediated immunoregulatory effect character-ized by a significant reduction in LPS-induced iNOS expression. In line, OCM from human colons inhibited LPS-dependent inflammatory cytokine expression in human monocytes-derived macrophages. Interestingly, the inflammatory marker CD68 was reduced by OCM from control patients but not from UC patients, suggesting epithelial dysfunction in UC pa-tients. Our results report new regulatory mechanisms in the colon and highlight the im-portance of developing new in vitro models to better characterize the relationship between the intestinal epithelium and immune mucosal cells.