As shown in Supplementary Fig. 4, I3C supplementation induced the expression of Cyp1a1 in the intestinal epithelium (Supplementary Fig. 4a) and reduced NEC severity (Supplementary Fig. 4b–d) in Il22-/- mice, illustrating that IL-22 was not required for the protective effects of AHR activation on NEC. This evidence concerns the gene CYP1A1 and necrotizing enterocolitis.