Interleukin-18 (IL-18) is a cytokine, a type of protein that plays a crucial role in the immune system. It is produced by various cells, including macrophages, and helps regulate immune responses by promoting the activation of T cells and natural killer cells. IL-18 is involved in the body's defense against infections and inflammation. IL-18 works in conjunction with other cytokines, such as interleukin-12, to enhance the production of interferon-gamma, which is important for fighting off pathogens. Dysregulation of IL-18 has been linked to several diseases, including autoimmune disorders and certain types of cancer, highlighting its significance in health and disease.