Interleukin-5 receptor alpha subunit (IL-5Rα; CD125), a type I cytokine receptor that pairs with the common beta chain (βc) to form the high-affinity IL-5 receptor. This receptor is selectively and highly expressed on eosinophils and basophils. IL-5 is the principal cytokine responsible for the growth, differentiation, recruitment, activation, and survival of eosinophils. In severe eosinophilic asthma, elevated levels of IL-5 drive the accumulation and persistence of eosinophils in the airways, leading to chronic inflammation, tissue damage, and bronchoconstriction.