Fas ligand expression and function. Peripheral T cells were activated by CD3-crosslinking and were maintained for 7 days in IL-2–containing medium (30 U/ml). T cells were then cultured for 24 hours at an E/T ratio of 10:1 in the absence or presence of CD3x19 bs ab (10 μg/mL). Control cultures were performed with medium alone (ie, only T cells plus Nalm-6), monospecific control antibodies (OKT3 and HD37 at 5 μg/mL), or control F(ab)′ fragments (FII23c IgG3, 5 μg/mL19). Anti-CD95 F(ab)′2 fragments (anti–APO-1 IgG3, 5 μg/mL) were used to block interaction between CD95/Fas and Fas ligand. After incubation, the remaining B lymphoma cells were removed from the coculture by immunomagnetic depletion with anti-CD19 and anti-CD20 as described.10 T-cell apoptosis was measured on the single-cell level as described.15