IFNA1 and infection: In that study, IFNα expression also peaked at day 4 p.i. but was less robustly induced, while IFNγ and other known inducers of IDO such as IL6 and TNFα displayed a delayed induction as late as days 7 or 14 p.i. (43), suggesting that the complex milieu of factors that can stimulate IDO1 expression are not synchronized during infection.