Interleukin-2 (IL-2) is a type of protein known as a cytokine, which plays a crucial role in the immune system. It is primarily produced by T cells, a type of white blood cell, and helps regulate the growth, development, and activity of immune cells. IL-2 is essential for the proliferation of T cells and B cells, which are vital for the body's defense against infections and diseases. In addition to its role in immune response, IL-2 is also used in medical treatments, particularly for certain types of cancer, such as melanoma and renal cell carcinoma. By boosting the immune system's ability to fight cancer cells, IL-2 therapy can enhance the effectiveness of other treatments and improve patient outcomes.