TPH1 and infection: Accordingly, the level of Trp decreased (Fig. 7c) while those of the indole pathway (including the Indole-3-propionic acid, Indole-3-lactic acid, Indole-3-carboxaldehyde, Indole-3-carboxylic acid, and Indoxyl sulfate) (Fig. 7d) increased in infection in Tph1−/− mice, whereas the levels of metabolites along the kynurenine pathway (Kynurenic acid and Xanthurenic acid), although increased in infection, were not significantly different from those detected in Tph1+/+ littermates, except for kynurenines (Fig. 7e).