IL-5, or Interleukin-5, is a type of protein known as a cytokine, which plays a crucial role in the immune system. It is primarily produced by a subset of immune cells called T-helper 2 cells. IL-5 is essential for the growth, differentiation, and activation of eosinophils, a type of white blood cell involved in allergic reactions and responses to parasitic infections. In addition to its role in promoting eosinophil production, IL-5 is also implicated in various allergic diseases, such as asthma and eosinophilic esophagitis. Targeting IL-5 with specific therapies has become a strategy for treating these conditions, helping to reduce inflammation and improve patient outcomes.