IFNG and macrophage activation syndrome: When untreated sHLH/MAS patients were analyzed, we found an area under the curve (AUC) of 0.93 [95% confidence interval (CI), 0.85-1.00, p<0.001] for pSTAT1 levels in unstimulated monocytes (Figure 4A) and an AUC of 0.92 (95% CI, 0.83-1.00, p<0.001) for pSTAT1 levels in monocytes stimulated with IFNγ (10 ng/ml) (Figure 4B).