Expression of the native form of perforin in stimulated PBMCs from the patient, his parents, and a healthy blood bank donor. (A) PHA- and IL-2–stimulated PBMCs were fixed and permeabilized, stained with FITC-conjugated antiperforin antibody (dG9; Ancell, Bayport, MN) or phycoerythrin (PE)–conjugated anti–granzyme A antibody (CB9; BD Pharmingen), and analyzed by flow cytometry. The experiment was performed 3 times with similar results. The normal range of perforin-positive cells in 3 healthy donors was 3.4% to 56% (average 14%) in 4 separate experiments. (B) Immunofluorescence assay shows expression of perforin in PBMCs stimulated with PHA and IL-2, fixed, permeabilized, incubated with FITC-conjugated antiperforin antibody dG9 (green), and counterstained with propidium iodide (red). Original magnification, × 1000.