IDO1 and inflammatory bowel disease: In IBD, the changes in the expression of IDO1 correlated positively with the changes in the expression of KYNU (slope = 0.79; R2 = 0.76), HCAR3 (slope = 0.84; R2 = 0.69), IL4I1 (slope = 0.32; R2 = 0.67), KMO (slope = 0.30; R2 = 0.63), and TDO2 (slope = 0.52; R2 = 0.62).