Interleukin-6 (IL-6) is a cytokine, a type of protein that plays a crucial role in the immune response. It is produced by various cells, including macrophages, T cells, and fibroblasts, and helps regulate inflammation and the body's response to infections. Elevated levels of IL-6 are often associated with chronic inflammatory conditions and autoimmune diseases. IL-6 is also involved in the process of hematopoiesis, which is the formation of blood cells. It influences the differentiation of B cells into antibody-producing cells and can affect the production of acute phase proteins during inflammation. Understanding IL-6 is important for developing treatments for diseases like rheumatoid arthritis and COVID-19.