Interleukin-6 (IL-6) is a type of protein known as a cytokine, which plays a crucial role in the immune system. It is produced by various cells, including macrophages, T cells, and fibroblasts, and helps regulate inflammation and immune responses. IL-6 is involved in the body's defense against infections and injuries. In addition to its role in immunity, IL-6 is also linked to various diseases. Elevated levels of IL-6 can be found in conditions such as rheumatoid arthritis, cancer, and COVID-19. Researchers study IL-6 to understand its functions better and to develop potential treatments for these diseases.