Reduced perforin expression in resting and activated NK cells of HPS2 patients. Expression profiles of perforin (mAb deltaG9) in unstimulated (A) and activated NK cells (B) from HPS2 patients (empty histograms) and from a perforin-deficient patient were overlaid with that of a healthy donor (filled histogram) to directly compare their fluorescence's mean. Pt 1: left panels; Pt 2: middle panels; perforin-deficient patient (FHL): right panels. Isotype-matched mouse IgG stained less than 0.1 % of cells. Expression of perforin was evaluated in parallel in NK cells from 10 healthy individuals. These experiments are representative of 5 independent experiments. (C) Confocal microscopy of perforin in IL-2–activated NK cells of HPS2 patients. NK cells from control donor (i) and Pt 1 (ii) were stained with antibodies against perforin (green) and Lamp-2 (red) as described in “Patients, materials, and methods.” Scale bars, 10 μm. Samples were analyzed using a Zeiss Axioplan 2 microscope (Carl Zeiss, Hertfordshire, United Kingdom) with Zeiss Plan-NEOFLUAR 100/1.3NA lenses mounted with a CoolSnap HQ camera (Roper Scientific, Tucson, AZ). Images were processed using Metamorph software (Molecular Devices, Downingtown, PA) and AutoDeblur + Autovisualize software (AutoQuant Imaging, Watervliet, NY).