Human IL-21 Serum & Plasma Onestep ELISA Kit

Interleukin-21 (IL-21) is a multifunctional type I cytokine primarily secreted by activated CD4+ T cells, including T follicular helper (Tfh) and Th17 subsets. It signals through a receptor complex consisting of a unique IL-21 receptor (IL-21R) and the common γ-chain, activating JAK-STAT, MAPK, and PI3K pathways. IL-21 plays a central role in modulating both adaptive and innate immune responses: it critically regulates B cell differentiation, class-switching, and antibody production; enhances the activity and expansion of CD8+ cytotoxic T cells and NK cells; and influences CD4+ T cell fate. Due to these potent immunoregulatory functions, IL-21 is deeply involved in the pathogenesis of autoimmune diseases (e.g., systemic lupus erythematosus, rheumatoid arthritis) and promotes anti-tumor immunity. Consequently, the IL-21 pathway is a promising therapeutic target, with strategies ranging from recombinant IL-21 as a potential immunostimulant in oncology to blocking antibodies for treating autoimmune and inflammatory conditions.