IL21 and systemic lupus erythematosus: Expression of T helper cells and its subtypes Th2, Th17, and T follicular helper cells is increased in all SLE cases and is accompanied by an increase in serum cytokines such as interleukin-6 (IL-6), interleukin-10 (IL-10), interleukin-17 (IL-17), and interleukin-21 (IL-2).