Increased expression of CD25 and CD69 on donor CD4⁺ T cells at 36 hours and on day 3 in spleens of IL-12–protected mice. Lethally irradiated B6 mice received A/J BMC and spleen cells plus TCD B6 BMC with or without IL-12 on day 0. Spleen cells were analyzed by three-color FCM to determine percentages of CD4⁺ D^d+ donor cells expressing CD25 (A) and CD69 (B). Similar results were obtained from six mice per group at each time point in two independent experiments.