The induction of Th17 cells in AIA is IL-23 mediated. A. WT mice were immunized with mBSA/CFA and 10 days later splenocytes were isolated and stimulated for four hours with PMA/Ionomycin, gated for CD4+ T cells and analyzed for intracellular IL-17A and IFN-γ expression. Numbers indicate percentage of positive cells within each quadrant. B-D. Antigen-induced arthritis was induced in WT and IL-23p19KO mice and at days 1 and 7, after i.a. mBSA injection, the splenocytes were isolated and stimulated for 4 h with PMA/Ionomycin and analyzed for intracellular IL-17A and IFN-γ expression on a CD4+ T cell gate. B. Numbers indicate percentage of positive cells within each quadrant. C and D. Quantification of flow cytrometric analyses from B; mean values and SEM are given for 6 to 12 mice per group from two to four independent experiments. E and F. On day 7 of AIA, splenic CD3+CD4+ T cells were FACS-sorted and gene expression was analyzed by quantitative RT-PCR for IL-17F and IL-22 respectively. Mean values and SEM are given for three mice. P-values were calculated using the student t-test.