Consistently, in the current study, the elevated expression of IDO1 induced by CRS facilitated the conversion of the Trp signaling to the toxic Kyn pathway, contributing to Kyn, 3-HK, and Quin accumulation in colon, which may aggravate gut integrity impairment, and increase periphery Kyn and other toxic metabolites, serving as an accomplice of depression. The gene discussed is IDO1; the disease is congenital rubella syndrome.