Cytotoxicity and granule exocytosis assays using stimulated PBMCs from the patient, his parents, an unrelated patient with CAEBV, and healthy donors. (A) PBMCs were stimulated with PHA and IL-2, cultured in IL-2 (effector cells), and flow cytometry showed lymphocyte phenotypes described in Figure 2B. The cells were incubated with [51Cr]-labeled L1210 target cells (Fas-deficient target cells) in the presence of anti-CD3 (UCHT-1; BD Pharmingen) and anti-Fas blocking antibody (ZB4; Beckman Coulter, Fullerton, CA) in a Fas-independent CTL killing assay. Cytotoxicity in this assay system is CD3-dependent, since T-cell receptor activation is required to trigger release of granules containing perforin and granzymes.20 The effector-to-target (E/T) ratio is indicated on the x axis and the percent specific lysis is indicated on the y axis. The percent lysis was calculated as follows: % lysis = (E–S)/(M–S) × 100, where E is the release from experimental samples, S is the spontaneous release, and M is the maximum release upon lysis with 2% NP-40. The gray band indicates the normal range of cytotoxicity seen in 4 healthy donors (data not shown). Cells from a healthy blood bank donor incubated in the absence of anti-CD3 antibody were assayed as a negative control. Flow cytometry showed the following lymphocyte phenotypes: donor 1: CD8 = 49%, CD56 = 42%; donor 2: CD8 = 55%, CD56 = 42%; patient: CD8 = 54%, CD56 = 25%; mother: CD8 = 50%, CD56 = 68%; father: CD8 = 91%, CD56 = 4%; unrelated patient with CAEBV: CD8 = 55%, CD56 = 40%. (B) PBMCs were stimulated with PHA and IL-2 followed by incubation in the presence (black bars) and absence (white bars) of plate-bound anti-CD3/anti-CD28 antibody. Secretion of β-hexosaminidase in the cell culture supernatant was measured to quantify the level of granule exocytosis.33 β-hexosaminidase release was expressed as a percentage of the enzyme in the supernatant divided by the total enzyme from cells lysed in 0.1% Triton X-100. Experiments in panels A and B were performed 3 times and a representative result is shown.