C1q binding to PBL or PHA-blasts sensitized with ATGs. PBL or PHA blasts were labeled with increasing amount of rabbit ATG (no. 95-07) or horse ATG (no. 1141) and then with autologous serum (solid line) or heat-inactivated serum as control (dashed line). C1q binding was detected by using FITC-goat anti-C1q polyclonal antibody and cell analyzed by flow cytometry as described in Materials and Methods. Representative of three independent experiments.