Defective IL-17 production and Th17 differentiation of Ikkα^AA CD4⁺ T cells. CD4⁺ T cells from WT (n = 4) and Ikkα^AA (n = 4) mice were cultured under either neutral (Th0) or Th17-inducing condition as indicated. (a) 72 h later, IL-17– and/or IFN-γ–producing cells were measured by flow cytometry after intracellular staining of cytokines. (b) Quantification of data shown in a. (c–g) 24 h after the initiation of the culture, total RNA was isolated and mRNA levels of the Th17 lineage genes were assessed by real-time RT-PCR. The lowest expression level of each gene was set to 1. The experiments were repeated at least three times with similar results. *, P < 0.05; **, P < 0.001.