Complement-mediated lysis of PBMC versus PHA-Blasts. PBMC or 3-day PHA-activated PBMC were labeled with ⁵¹Cr and incubated with rabbit ATG (no. 95-07) (▪), horse ATG (no. 1141) (•), control horse (○) or rabbit IgG (□) or the anti-CD52 MoAb CAMPATH-1M (IgM) (▴) at the indicated concentrations, for 30 minutes at 37°C, in the presence of 10% autologous serum. Results are expressed as specific release as defined in Materials and Methods (mean ± SEM of three different experiments).