Interleukin 5 (IL-5) is a member of the short-chain 4-α-helical bundle subset of hematopoietic cytokines. It binds to the specific α receptor, which in turn recruits the common β receptor that initiates signaling via JAK/STAT and MAPK pathways. IL-5 is produced by Th2 cells, eosinophils, activated mast cells, and ILC2 cells. IL-5 affects the differentiation, activation, and survival of eosinophils, thus playing an important role in allergic inflammation, asthma, and parasite immunity. Stimulation of eosinophils with IL-5 leads to their activation, upregulation of CD11b expression, and inhibition of apoptosis (Shearer).