Il18 deficiency mimics MyD88 deficiency susceptibility to polyp formation. Cohorts of 6–20 mice/group were subjected to AOM/DSS treatment as depicted by the scheme. At the end of the first DSS cycle, mice were analyzed for bleeding (A). 100 d after AOM administration, the Il1r1^−/−, Il18^−/−, and their corresponding controls were euthanized and colonic polyps were counted (B). For comparison, Myd88^−/− mice were tested simultaneously. Because of their susceptibility to the treatment, the number of polyps was scored at the completion of the second DSS cycle (C). The data shown in A–C correspond to a representative experiment out of three performed. Il18^−/− and Il1r^−/− mice and their corresponding heterozygote and WT littermates were subjected to AOM/DSS treatment as indicated by the scheme. At the completion of the experiment, the number of colonic polyps was counted (D and E). The data shown in D and E correspond to a representative experiment out of two performed using littermate controls. Data represent means ± SE. **, P < 0.01; ***, P < 0.001.