mATG-treated cells are functionally suppressive in vitro. C57BL/6 mouse splenocytes were cultured with 100 μg/mL mATG or rabbit IgG in the presence of 200 U/mL IL-2, and 5 days following initiation of culture cells were evaluated for their ability to suppress the proliferative responses of normal splenocytes. Variable numbers of mATG- or rabbit IgG–treated mouse splenocytes were added to normal mouse splenocytes stimulated with anti-CD3/anti-CD28 beads as described in “Suppression assays.” Data are means (± SD) of 3 replicates from a representative of 5 separate experiments.