Flow cytometric assessment of pSTAT1 expression on monocytes. (A) Gating of monocytes on side scatter vs. CD14 FITC. (B) Overlay of a patient with complete STAT1 deficiency shows an abolished response to both IFN-γ compared with a healthy control. (C) Overlay of a patient with complete STAT1 deficiency shows an abolished response to IFN-α compared with a healthy control, where green is patient unstained, red patient stained, and blue control stained. (D) Baseline serum IFN-γ levels in patients with STAT1 deficiency and controls (Asterisks indicate statistical significance: P 0.0015**).