IL21 and rheumatoid arthritis: We found that the mRNA levels of the genes encoding the proinflammatory cytokines IFN-γ, TNF-α, IL-4, IL-21, and IL-17A were higher in the PBMCs of patients with RA (Fig. 2b), and the IFN-γ, TNF-α, IL-10, and IL-17A mRNA levels were positively correlated with the mRNA level of PD-1Δex3 (Fig. 2c–h).