Perforin deficiency detected by flow cytometry. Histogram plots depicting flow cytometry analysis of peripheral blood lymphocytes from the patient described in case 1. Upper panels depict patient cells, while the lower panels depict normal controls. Results for natural killer (NK) cells are shown on the left, while those for CD8+ T lymphocytes are shown on the right. Isotype controls are represented by the gray histograms, and perforin antibody detection is represented by the histograms in magenta (NK) or green (CD8+).