IFNG and systemic-onset juvenile idiopathic arthritis: Furthermore, de Jager and colleagues reported a defective IFN-γ production by NK cells of sJIA patients upon stimulation with IL-18 [91] and microarray analysis demonstrated an absence of IFN-γ -induced gene expression in peripheral blood mononuclear cells (PBMCs) from active sJIA patients [84,92,93].