These studies also show that the indoleamine 2,3-dioxygenase (IDO), a key enzyme of tryptophan metabolism, is involved in CGD-associated inflammation and tryptophan catabolites (kynurenines) could be therapeutically useful to regulate and dampen hyperinflammation [135,136] although the regulation of this pathway in human CGD is different [137-140]. Here, IDO2 is linked to chronic granulomatous disease.