[Interactions and biological mechanisms of action of molecular signal peptides. II. Interleukin 2 (IL-2)].

Interleukin 2 (IL-2) is predominantly produced by T-helper cells (TH1) having the phenotype CD4+, and by subpopulations of thymocytes after antigenic or mitogenic stimulation. IL-2 causes an indefinite growth of T-cells, and its function depends on binding to IL-2 receptors (IL-2R alpha and IL-2R beta). Thus the immune response of T cells is controlled through the expression of the IL-2 receptors and the IL-2 binding. IL-2 receptors are expressed not only by T-cells but also by B-cells, NK cells, monocytes, thymocytes, thymic stroma cells, oligodendrocytes and endothelial cells. This explains the various functions of IL-2, such as increased immunoglobulin production, growth of certain B-cell subpopulations, macrophage-dependent cytotoxicity, growth and differentiation of oligodendrocytes and proliferation of lymphokine activated killer (LAK) cells. Abnormal production of IL-2 may lead to autoimmune diseases, immunodeficiencies and, under certain circumstances, to T-cell leukemia. With antibodies against the IL-2 receptors the binding of IL-2 may be blocked to avoid auto-aggressive destruction in autoimmune diseases. LAK cells increase the growth of NK cells and T-cell cytotoxicity against transformed cells. LAK cells, especially those from tumor infiltrating lymphocytes, in conjunction with IL-2 have already been used with promising initial results in the treatment of distant metastases. In the future LAK cell therapy with IL-2 may be adopted to prevent metastases and second primary tumors in high-risk patients with head and neck cancer.