Lytic activity of EBV-specific CD8+ and CD4+ T cells. A) Cytotoxic activity was tested by standard 4 h 51Cr-release assay in the presence of "cold" K562 at a 5:1 ratio of "cold": "hot" target. B) Lytic mechanisms involved in cytotoxicity. CD4+ T cell line cytotoxicity was evaluated in the presence of CMA and EGTA that block perforin-based pathway, and BFA and anti-FasL mAb that interfere with Fas/FasL-based pathway. Figure shows mean values from 3 independent experiments carried out for each donor cell line.