IL5RA (interleukin-5 receptor subunit alpha) is a cell surface receptor critical for eosinophil biology and immune regulation. It functions as a heterodimeric receptor with CSF2RB that binds interleukin-5 (IL-5), mediating eosinophil survival, differentiation, and chemotaxis 1. The receptor constitutively associates with JAK2 kinase, and upon IL-5 stimulation, undergoes heterodimerization and activates the JAK-STAT signaling cascade 2. IL5RA exhibits complex transcriptional regulation through dual promoters (P1 and P2) with distinct temporal activity patterns during eosinophilopoiesis, controlled by transcription factors including GATA-1, PU.1, and C/EBP family members, generating both transmembrane and soluble isoforms with opposing signaling properties 3. Beyond eosinophils, IL5RA is expressed on basophils, mast cells, and epithelial cells 4. Clinically, IL5RA targeting via monoclonal antibodies (benralizumab) effectively treats eosinophilic disorders including severe asthma, where it reduces oral glucocorticoid requirements by 75% 5, eosinophilic granulomatosis with polyangiitis 6, and hypereosinophilic syndrome 7. Genetic variations in IL5RA associate with asthma-related eosinophilia and sporadic IgA nephropathy 89. Additionally, elevated plasma IL5RA levels constitute a causal mechanism for multiple myeloma genetic predisposition 10.