The function of ENSG00000188676 (IDO2, indoleamine 2,3-dioxygenase 2) is as follows. Catalyzes the first and rate limiting step of the catabolism of the essential amino acid tryptophan along the kynurenine pathway (PubMed:17671174). Involved in immune regulation. May not play a significant role in tryptophan-related tumoral resistance (PubMed:25691885). {ECO:0000269|PubMed:17671174, ECO:0000303|PubMed:25691885}.