Effect of blood components on CTL activity. Cytotoxic activity of EBV specific CTL evaluated by a 4-hour ⁵¹Cr release assay performed at 30:1 (▪), 10:1 (▧), and 3:1 (□) effector:target cell ratio in absence (C) and in presence of different blood components before (1) and after (2) immunodepletion of sHLA-I molecules (A). Cytotoxic activity of EBV specific CTL evaluated in absence (lane 1) and in presence (lane 2) of RBC-30 and after preincubation of either effector (lane 3) or target (lane 4) cells with RBC-30 (B). Percentage of viable (□) and apoptotic (▪) EBV-specific CTL after incubation for 1 hour with RPMI medium (1), RBC-30 (2), and RBC-30 immunodepleted of sHLA-I (3), sFasL (4), or sHLA-I and sFasL (5) (C).