Cytokines are small proteins that play a crucial role in cell signaling within the immune system. They are produced by various cells, including macrophages, lymphocytes, and endothelial cells, and help regulate immune responses, inflammation, and the formation of blood cells. Cytokines can act on the same cells that produce them or on nearby cells, influencing their behavior and function. There are several types of cytokines, including interleukins, tumor necrosis factors, and chemokines. Each type has specific functions, such as promoting cell growth, directing immune cells to sites of infection, or regulating inflammation. Dysregulation of cytokine production can lead to various diseases, including autoimmune disorders and cancer.