For this reason, we investigate whether or not Kyn and IDO activity is potentially useful biomarkers in pediatric AIH.Between January 2016 and January 2017, children of AIH type-1 (AIH-1, n = 37), AIH type-2 with liver kidney microsome-1 autoantibodies (AIH-2-LKM-1, n = 8), and autoantibody-negative Wilsons Disease (WD, n = 8) and alpha-1 anti-trypsin deficiency (AATD, n = 10), were enrolled in a cross-sectional survey of Kyn and Trp levels and Kyn/Trp ratios (IDO activity) by HPLC, and neopterin levels by ELISA.The mean Kyn and mean Kyn/Trp ratios of AIH-1 with smooth muscle antigen (SMA) 1.85 μM and 27 μmole/mmole, and AIH-2-LKM-1; 1.7 μM and 28.6 μmole/mmole were lower than that of the WD; 2.2 μM p = 0.03 and 33 μmole/mmole p = 0.02 and of AATD; 2.3 μM, p = 0.02 and 55 μM, p = 0.001.