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 cell that produces them or on nearby cells, influencing their behavior and function. There are different types of cytokines, including interleukins, interferons, and tumor necrosis factors. Each type has specific functions, such as promoting cell growth, activating immune cells, or inducing cell death. Dysregulation of cytokine production can lead to various diseases, including autoimmune disorders and cancer.