A OT-II TCR transgenic CD4 T cells with ICOS-WT, KO, and YF genotype were polarized to Th17 lineage in vitro as described in Materials and Methods. The percentages of IL-17 producing cells among CD4+ CD44+ cells are depicted. B LN CD4 T cells purified from ICOS-WT, KO, and YF mice were stimulated in the presence of IL-23 as described in Materials and Methods. The percentages of IL-17 producing cells among CD4+ CD44+ cells are depicted. Data are presented as mean ± SD (4 replicates of ICOS-WT, ICOS-KO, and ICOS-YF CD4 T cell cultures) from one representative experiment out of three independent experiments with consistent results. * p<0.05, ** p<0.01, *** p<0.001.