Used in immunological research to study eosinophil activation and regulation, particularly in models of allergic inflammation and asthma. The Fc tag enables easy detection and purification, and enhances stability and half-life in assays. Commonly employed in ELISA, flow cytometry, and receptor binding studies. Also utilized in the development of anti-eosinophilic therapies and as a reference standard in bioassays evaluating IL-5 receptor antagonists.