This may indicate that the potent induction of IFN-γ could be controlling parasite load and simultaneously activating the tryptophan degradation pathway via IDO1 in malaria-naïve individuals, and that in non-naïve individuals in which adaptive immunity is active, the overall response shifts toward lower IFN-γ levels and anti-malaria antibodies, and is independent of parasite load. This evidence concerns the gene IDO1 and malaria.