Spontaneous Th2 polarization of CD4⁺ T cells in naive IRF-2^-/- mice. (A) Cytokine production by freshly purified whole or CD62L⁺CD4⁺ T cells on CD3/CD28 stimulation. Means and SDs are shown for duplicate cultures with control (□) and IRF-2–deficient (▪) CD4⁺ T cell preparations, respectively. (B) Serum IgE titers of control (○) and IRF-2^-/- mice (•). Each circle represents an individual mouse. (C) Expression of T1/ST2 was examined for gated CD4⁺ T cells. The percentages of T1/ST2⁺ cells within CD4⁺ T cells are shown in the dot plots. The percentages of T1/ST2⁺ cells among CD4⁺ T cells in individual mice were plotted for control (○) and IRF-2^-/- mice (•) in the right panel. Values were significantly different between these 2 groups (P < .05). (D) In vitro differentiation of Th1 and Th2 cells from OT-II TCR tg CD4⁺ T cells in the presence of T cell-depleted spleen cells as examined by flow cytometry (top row) or by ELISA (bottom row). In the bottom panels, data obtained with control (□) and IRF-2–deficient (▪) cells are represented, respectively. (E) IL-12p40 production by T, B, NK, NKT and erythroid cell-depleted spleen cells from control (□) or IRF-2^-/- mice (▪) in cultures with OT-II TCR tg CD4⁺ T cells in the absence (-) or presence (+) of OVA peptide. Data shown are means and SD of duplicate cultures. Representative of at least 3 independent experiments (A,D,E).