IDO1 and hereditary elliptocytosis: Furthermore, we observed that there were significant differences in TRP, kynurenine, and 2,3-pyridinedicarboxylic acid (quinolinic acid, QA) between the two groups (Table 3; Figures 3A,C); these findings suggested that the occurrence of HE after TIPS may be related to the kynurenine/IDO pathway.