IFNγ, type II IFN, would be the prototypic “macrophage-activating factor” which could increase cytokine and chemokine production, phagocytosis, and the intracellular killing of microbial pathogens by macrophages, thus playing important pathogenic roles in the development of AOSD and MAS (28, 54). This evidence concerns the gene IFNG and adult-onset Still disease.