IL17A and Arthritis: Interestingly, although the anti-IFN-γ group had similar levels of serum and elevated levels of paw IL-17 in comparison to the anti-IFN-γ + anti-IL-4 groups (Figures 3b and 3c) and the arthritis was completely dependent on IL-17, the numbers of Th17 cells in vivo were not increased (Figures 6a, c and 6d).