IL21 and systemic lupus erythematosus: For SLE, there are several studies in mouse models and humans, showing that the progressive disease is associated with lower expression of TNF-α, IFN-γ, and IL-2 (Humrich et al., 2010) as well as higher expression of PD-1 (Jiao et al., 2014), IL-21 (Wang et al., 2014), and IL-10 (Facciotti et al., 2016).