Interleukin-13 (IL-13) is a cytokine, a type of signaling molecule in the immune system. It is primarily produced by T-helper 2 (Th2) cells and plays a crucial role in regulating immune responses, particularly in allergic reactions and asthma. IL-13 helps stimulate the production of IgE antibodies and promotes the activation of B cells, which are essential for the body's defense against pathogens. IL-13 also influences the function of various cells, including macrophages and epithelial cells. It contributes to tissue remodeling and inflammation, which can lead to conditions like asthma and chronic rhinosinusitis. Understanding IL-13's role is important for developing targeted therapies for these diseases.