Blocking of cytotoxic activities of type I and type II clones by anti-Fas MoAb. ⁵¹Cr-labeled target cells no. 4 (Table 1) were incubated with 500 ng/mL or 5 μg/mL of anti-Fas MoAb or medium alone for 60 minutes at 37°C. Then effector cells were added at an E:T ratio of 2:1 and a standard 4-hour ⁵¹Cr release assay was performed. The percentage of specific lysis is indicated. (▪) Control; (▨) anti-Fas MoAb (500 ng/mL); (▧) anti-Fas MoAb (5 μg/mL). Target: A*2402/3303, B*4403/5201, DRB1*1406/1502, DQB1*0301/06.