Although receiving RA administration, AGN‐treated mice developed more severe colitis with more Th17 cell infiltration and higher epithelial expression of Saa1, Saa2, and Cebpa (Figure 4J–L; Figure S6F,G, Supporting Information), suggesting that RA could regulate C/EBPA in colitis via RARs. This evidence concerns the gene RARS1 and colitis.