Abolished STAT1 phosphorylation in response to IFN-γ and altered baseline serum IFN-γ levels in patients with complete IFN-γR2 deficiency. (A) Overlay of pSTAT1 expression in a healthy control and patient with CR IFN-γR2 deficiency showing an abolished response to increasing concentrations of IFN-γ (green is unstained, sky blue 10 IU/ml, violet 100 IU/ml, magenta 1,000 IU/ml, and red 10,000 IU/ml concentration of IFN-γ). (B) Baseline serum IFN-γ levels of patients with complete IFN-γR2 deficiency and controls (Asterisks indicate statistical significance: P 0.0002***).