CARD9 and colitis: This negative correlation could also be observed in dextran sulfate sodium-induced colitis in mice.102 Furthermore, the microbiota from mice deficient in caspase recruitment domain 9 (CARD9), a susceptibility gene for colitis,103 failed to produce AHR ligands metabolized from tryptophan.104 Lamas et al. found that the subsequent reduction in AHR activity was associated with reduced IL22 expression and enhanced susceptibility to colitis.