Used to measure interleukin-21 (IL-21) levels in biological samples such as serum, plasma, or cell culture supernatants from mice. It is commonly applied in immunology research to study T cell and B cell activity, as IL-21 plays a key role in immune regulation, inflammation, and autoimmune diseases. The kit enables accurate quantification of IL-21, supporting studies on immune responses, vaccine development, and therapies targeting cytokine signaling. It is also used in preclinical studies to evaluate the effects of drugs or genetic modifications on immune function in mouse models.