DCH-mediated cytotoxicity of isolated CD4+ and CD8+ T cells. A two-color FACS®-based assay was performed. Kato III target cells were prelabeled with PKH26 and mixed with isolated human CD4+ or CD8+ T cells at an E/T ratio of 10:1. We incubated 10 µg/ml DCH with the cells for 16 h at 37°C and 5% CO₂. A control reaction without fusion protein was included. PI was added to discriminate between live and dead target cells. Error bars indicate standard deviations from duplicate determinations.