Used to measure levels of interleukin-9 (IL-9) in biological samples such as serum, plasma, or cell culture supernatants. Commonly applied in immunology research to study T cell responses, allergic inflammation, and autoimmune diseases. Helps researchers understand the role of IL-9 in conditions like asthma, lupus, and certain cancers. Suitable for quantitative analysis, enabling comparison of IL-9 expression across experimental groups. Widely used in preclinical studies and biomarker validation.