It was demonstrated that Asc-/-, Caspase-1-/-, Nlrp6-/- and Il18-/- mice, but not Il1b-/- or Il1R-/- mice, developed severe colitis after dextran sodium sulphate (DSS) treatment and that co-housed wild type mice were also more susceptible to DSS treatment, indicating that the microbiota is responsible for the exacerbation of DSS-induced colitis (51, 52). This evidence concerns the gene IL18 and colitis.