IL-17 receptor signaling is critical for the progression of AIA. A. WT, IL-23p19KO and IL-17RAKO mice were immunized with mBSA/CFA and mono-arthritis was induced one week later by an i.a. injection of mBSA. At days 1, 2, 4, 7 and 10 macroscopic scores were assessed. Mean values and SEM are given for six mice per group. * P < 0.01 WT vs IL-23P19KO and #, P < 0.01 WT vs IL-17RAKO. B. At day 7 of AIA, splenocytes from WT, IL-23p19KO and IL-17RAKO were isolated and stimulated for four hours with PMA/Ionomycin and analyzed for intracellular IL-17A and IFN-γ expression on a CD4+ and TCRγδ+ T cell gate. Numbers indicate percentage of positive cells within each quadrant and each dot plot shows a representative mouse from three mice per group analyzed.