In line with this, we observed significantly increased concentrations of the anti-inflammatory cytokine IL-10 in the bronchoalveolar space of ICOS agonist treated mice on day 8 post infection (Figure 5B) as well as slightly elevated BALF and serum kyn/trp which indicates accelerated tryptophan breakdown that is most probably due to activity of the immune regulatory enzyme indoleamine 2,3-dioxygenase (IDO) (Figure 5C). Here, IDO1 is linked to infection.