IFNG and hemophagocytic syndrome: IFN-γ predominantly produced by NK and T cells is a pleiotropic cytokine with multiple effects on the inflammatory response and on innate and adaptive immunity. Aberrant production of IFN-γ underlies a number of hyperinflammatory or immune-mediated diseases, such as primary hemophagocytic lymphohistiocytosis (HLH), various forms of secondary HLH, including MAS, and cytokine release syndrome [16, 17].  The statistical differences especially in serum IFN-γ level were lost in MAS-KFD versus SJIA-MAS.