Amongst several identified proteins in the in vitro model (including tryptophanyl-tRNA synthetase, indoleamine 2,3-dioxygenase, heterogeneous nuclear ribonucleoprotein JKTBP, interferon-induced 35 kDa protein, proteasome subunit LMP2, and argininosuccinate synthetase), overexpression of indoleamine-2,3-dioxygenase (IDO) was confirmed in the purified IEC from IBD patients in comparison to normal mucosa [131]. Here, IDO1 is linked to inflammatory bowel disease.