Interleukins are a variety of lymphokines, that is, polypeptides produced by activated LYMPHOCYTES. They are involved in signalling between cells of the immune system (see IMMUNITY) with their interaction controlling the immune response of cells; they also participate in HAEMOPOIESIS. There are seven types, interleukins 1 to 7. For example, interleukin 1 is produced as a result of INFLAMMATION and stimulates the proliferation of T and B lymphocytes, enhancing the immune response by stimulating other lymphocytes and activating dormant T cells. Interleukin 2 has anti-cancer effects as it is able to activate T lymphocytes to become killer cells which destroy foreign antigens (see ANTIGEN) such as cancer cells; this anti-cancer effect is being developed for clinical use. Interleukin 6 is used as a BIOMARKER to assess the degree of inflammation present. The remaining interleukins have a range of properties in cell growth and differentiation.