CD28-expanded T cells contain normal numbers of regulatory T cells. (A) Frequencies of CD4⁺CD25⁺ cells in lymph nodes of a normal PVG rat without (top left panel) and with (top right panel) a single injection of 1 mg of CD28 superagonist 3 days earlier, and in ATXBM rats reconstituted as in Figure 4 with (lower right panel) or without (lower left panel) CD28 stimulation. (B) Concanavalin A induced cytokine production by lymph node cells from T-cell reconstituted ATXBM rats reconstituted with (○) or without (•) CD28 stimulation. Unstimulated controls contained no detectable cytokines. Means and SDs are shown.