The interleukin-2 receptor.

The human body defends itself against foreign invaders such as bacteria and viruses by a defense system that involves antibodies and thymus-derived lymphocytes (T cells). A major advance over the past decade has been the demonstration that the diverse cells within the immunological network communicate with each other not only by cell/cell contact but also by an array of hormone-like proteins termed interleukins or lymphokines. Of all the lymphokines involved in this network of cellular communication, the most is known about the structure and function of interleukin-2 (IL-2)' and its specific receptor. IL-2 plays a pivotal role in the growth and function of T lymphocytes. In addition, it affects the activities of B lymphocytes, monocytes, natural killer, and lymphokineactivated killer cells. T cells mediate important regulatory functions such as help and suppression as well as effector functions including the production of lymphokines and the cytotoxic destruction of antigen-bearing cells. Successful T cell-mediated immune responses require that these cells change from a resting to an activated state which requires two sets of signals from cell surface receptors to the nucleus. The first signal is initiated when an appropriately processed and presented antigen interacts with the heterodimeric T cell receptor for that specific antigen. Following this encounter, T cells enter a program of activation leading to the de novo synthesis and secretion of IL-2 (1-3). Resting T cells do not express high affinity IL2R, but receptors are rapidly expressed on T cells after activation with antigen or mitogen (3, 4). The interaction of IL2 with its induced cellular receptor then triggers proliferation of these cells culminating in the emergence of effector T lymphocytes mediating helper, suppressor, or cytotoxic functions. The study of the interleukin-2 receptor (IL-2R) and its lymphokine has provided a framework for understanding the cellular and molecular events that are involved in the regulation of the immune response. Furthermore, an understanding of IL-2 and its receptor has opened the way for novel therapeutic approaches for a wide array of clinical conditions including leukemia/lymphoma, autoimmune disorders, and organ allograft rejection. The intent of this article is to summarize the information on the ILSR with special reference to the most seminal discoveries and recent advances. Comprehensive recent reviews are available to provide more detailed information (3, 5-9).