IL21 and autoimmune disease: Th17 cells differentiate in response to IL-1β, IL-6, IL-23, and TNF-α; secrete IL-17A, IL-17F, and IL-21; and play a critical pathogenic role in T cell-mediated autoimmune diseases (Reddy et al., 2004; Wraith et al., 2004; Chen et al., 2012).