Lack of phosphorylated STAT4 upon IL-12 stimulation, as shown by FACS analysis. PHA-T-cell blasts from a positive control (C+), a negative control (C-), and the patient (P) were left unstimulated (plain line) or were stimulated (dotted line) with IFN-α (10⁵ U/mL) (left) for 30 minutes or with IL-12 (100 ng/mL) (right) for 15 minutes. Cells were fixed by PFA and methanol, permeabilized with saponin, and stained with a phospho-STAT4 rabbit polyclonal Ab (Zymed) (or matched isotype control), followed by goat anti-rabbit Alexa Fluor 488 (Molecular Probes).