Increased STAT3 activity in patient-derived EBV-transformed cell lines leads to decreased phosphorylation of other STAT molecules. (A) Impaired STAT5 phosphorylation in EBV-transformed cell lines derived from GOF STAT3 patients. Cells from patients (red) and healthy controls (blue) were stimulated with IL-2 (80 U/mL) and pSTAT5 measured by flow cytometry after 20 minutes. Numbers indicate the difference in MFI of phospho-STAT5 obtained by subtracting the MFI of unstimulated from stimulated samples. Yellow lines represent unstimulated patient samples; filled histograms, unstimulated healthy control samples. (B) Impaired STAT1 phosphorylation in EBV-transformed cell lines derived from GOF STAT3 patients. Cells from patients (red) and healthy controls (blue) were stimulated with IFN-γ (500 ng/mL) and pSTAT1 measured by flow cytometry after 20 minutes. Numbers indicate the difference in MFI of phospho-STAT1 obtained by subtracting the MFI of unstimulated from stimulated samples. Yellow lines represent unstimulated patient samples and filled histograms unstimulated healthy control samples. MFI, mean fluorescence intensity.