IL17A and Arthritis: In addition, GM-CSF (encoded by Csf2)-deficient (Csf2−/−) SKG mice were highly resistant to the induction of autoimmune arthritis by mannan as were Il17a−/− SKG mice, indicating a crucial role of GM-CSF for arthritis development in SKG mice (Figure 1C; Hirota et al., 2007a).