title: Interleukin 2 regulates its own receptors.
abstract: The cell surface density of high-affinity membrane receptors for the T-lymphocytotrophic hormone interleukin 2 (IL-2) determines the rate of T-cell-cycle progression. Since 10-fold greater numbers of IL-2 receptor molecules were found by using a radiolabeled monoclonal antibody reactive with IL-2 receptors (anti-Tac) compared with binding of IL-2, the functional relationship of the binding sites recognized by both of these ligands was assessed. In the presence of cycloheximide, IL-2 binding sites declined with a half-time (t1/2) of 2.6 hr, whereas the decay of anti-Tac binding sites was much slower (t 1/2 = 6.4 hr). Moreover, after limited membrane proteolysis, the half-time for the reappearance of IL-2 binding sites was remarkably similar to its decay (t 1/2 = 2.2 hr), while Tac antigen reappearance was markedly retarded, returning to only 20% of original levels within 5 hr after proteolysis. Addition of homogeneous immunoaffinity-purified IL-2 to cell populations that expressed equivalent IL-2 and anti-Tac binding sites resulted in a time- and temperature-dependent 8- to 10-fold enhancement of Tac epitope expression and, simultaneously, a 20-30% diminishment of detectable high-affinity IL-2 binding sites. As the magnitude of the IL-2-dependent proliferative response correlated with the density of high-affinity IL-2 binding sites, rather than Tac antigen levels, quantitation of Tac epitope density does not provide a reliable indication of IL-2-responsiveness among activated T-cell populations. Instead, IL-2-receptor interactions actually promote the loss of IL-2 responsiveness by diminishing the density of high-affinity binding sites at the time that Tac antigen levels are increased.
authors.forename: K A
authors.initials: KA
authors.lastname: Smith
authors.forename: D A
authors.initials: DA
authors.lastname: Cantrell
mesh_terms: D000954:Antigens, Surface / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D006207:Half-Life; D006801:Humans; D007376:Interleukin-2 / Q000378:metabolism*; D011971:Receptors, Immunologic / Q000378:metabolism; D015375:Receptors, Interleukin-2; D013601:T-Lymphocytes / Q000166:cytology; D013696:Temperature; D013997:Time Factors; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7
chemical_list: D000954:Antigens, Surface; D007376:Interleukin-2; D011971:Receptors, Immunologic; D015375:Receptors, Interleukin-2; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7