IL-4, or Interleukin-4, is a type of cytokine, which is a protein that plays a crucial role in the immune system. It is primarily produced by T-helper cells, particularly Th2 cells, and is important for regulating immune responses, especially in allergic reactions and asthma. IL-4 promotes the differentiation of B cells into plasma cells, leading to the production of antibodies. Additionally, IL-4 influences the activity of various immune cells, including macrophages and eosinophils. By encouraging the growth and activation of these cells, IL-4 helps the body respond to parasitic infections and contributes to the development of Th2 responses, which are associated with allergic diseases.