Drug analog inhibition of indoleamine 2,3-dioxygenase (IDO) activity modifies pattern recognition receptor expression and proinflammatory cytokine responses early during influenza virus infection

Influenza virus is recognized by PRRs, which are critical in the early response to virus infection and induction of proinflammatory cytokines. IDO is increased in the lung of mice immediately following influenza infection, and the presence of IDO has been shown to mediate immune suppression through depletion of trp and reduction in IL-6 production. To determine the role of IDO activity in the early immune response to influenza infection, IDO activity was inhibited using the synthetic analog, 1MT. The results show that IDO inhibition enhanced proinflammatory cytokine gene and protein expression at 24 and 48 h postinfection, respectively, compared with control-treated mice and affected PRR expression. The enhanced proinflammatory response in the presence of 1MT was attributed to macrophages in the airways, as Raw264.7 and primary AMs showed enhanced production of IFN-beta, IL-1 beta, IL-6, and TNF-alpha in the presence of 1MT. These findings provide important knowledge for the role of IDO during initial host response to influenza infection.