IDO2 and diabetes mellitus: 3-OH-KYN: 3-hydroxykynurenine; BBDP: BioBreeding diabetes-prone rats; DMT1: diabetes mellitus type 1; DMT2: diabetes mellitus type 2; GDM: gestational diabetes mellitus; HIV: human immunodeficiency virus; IDO: indoleamine 2,3-dioxygenase; IR: insulin resistance; KYN: kynurenine; KYNA: kynurenic acid; QUIN: quinolinic acid; Trp: tryptophan.