Interleukin-5 (IL-5) is a cytokine, a type of signaling molecule in the immune system. It is primarily produced by T-helper cells and plays a crucial role in the growth and activation of eosinophils, a type of white blood cell involved in allergic reactions and responses to parasitic infections. IL-5 helps regulate the production and survival of eosinophils in the bone marrow and promotes their migration to tissues. Elevated levels of IL-5 are often associated with conditions like asthma and eosinophilic esophagitis, making it a target for specific therapies aimed at reducing eosinophil-related inflammation.