By stimulating the indoleamine 2,3-dioxygenase (IDO) pathway, the early production of IFN-γ would condition dendritic cells to the further activation of a population of tolerogenic T regulatory cells, which would produce IL-10 and transforming growth factor beta (TGF-β), inhibiting the Th2 pathway and preventing the development of sensitization and allergy to A. fumigatus. The gene discussed is IDO1; the disease is allergic disease.