Furthermore, administration of three Lactobacillus strains (L. murinus CNCM I-5020, L. reuteri CNCM I-5022, and L. taiwanensis CNCM I-5019) capable of degrading tryptophan to colitis-susceptible Card9 (caspase recruitment domain family member 9)-knockout mice attenuates colitis and rescues the mucosal expression of Il22, and of its target genes Reg3b and Reg3g, in an AhR-dependent manner. Here, AHR is linked to colitis.