IDO1 and infection: We found that IDO1 was promptly induced in infection at the protein (Figure 4A) and gene (Figure 4B) expression levels, maintained elevated thereafter and was associated with increased levels of kynurenines, downstream products of IDO1 with immunoregulatory functions [44], [45] (Figure 4C) and increased kynurenine to tryptophan ratio [43] (Figure 4D).