title: Dexamethasone enhances CTLA-4 expression during T cell activation.
abstract: T cell activation is enhanced by the costimulatory interaction of B7 on antigen-presenting cells and CD28 on T cells, resulting in long-term T cell proliferation, differentiation and production of large amounts of cytokines, such as interleukin (IL)-2. CTLA-4 is a co-stimulation receptor that shares 31% homology with CD28 and binds B7 family members with higher affinity. CTLA-4 is transiently expressed intracellularly and on the cell surface following activation of T cells. We have studied the kinetics of CTLA-4 expression and the effects of dexamethasone on CTLA-4 expression during T cell activation in cultures of mouse spleen cells stimulated by a mixture of immobilized anti-CD3 and anti-CD28 monoclonal antibodies (anti-CD3/CD28 mAb) or concanavalin A (ConA). CTLA-4 expression peaked on day 2 and returned to background levels after 7 days. Dexamethasone was found to potentiate CTLA-4 expression in a dose-dependent manner with an EC50 effective concentration 50%) of about 10(-8) M. In contrast, other immunosuppressive agents, such as rapamycin or cyclosporin A had no or an inhibitory effect on CTLA-4 expression, respectively. Dexamethasone also stimulated CD28 expression, but inhibited IL-2R expression during anti-CD3/CD28 mAb-induced mouse splenic T cell activation. Western blot analyses of lysates of activated mouse T cells showed that dexamethasone increased CTLA-4 protein levels twofold during anti-CD3/CD28 mAb-induced activation. Dexamethasone also enhanced CTLA-4 messenger RNA twofold as quantified by ribonuclease protection assay. The effects of dexamethasone on CTLA-4 expression were glucocorticoid-specific and completely inhibited by the glucocorticoid receptor antagonist mifepristone (RU486), indicating that the effect of dexamethasone on CTLA-4 expression is mediated through the glucocorticoid receptor. In conclusion, the immunosuppressive agent dexamethasone actually stimulates CTLA-4 expression, which is involved in downregulation of T cell activation.
authors.affiliation: Department of Pharmacology, Amgen Inc., Thousand Oaks, California 91329-1789, USA.
authors.forename: M
authors.initials: M
authors.lastname: Xia
authors.forename: J
authors.initials: J
authors.lastname: Gasser
authors.forename: U
authors.initials: U
authors.lastname: Feige
mesh_terms: D000069594:Abatacept; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000096:biosynthesis / Q000276:immunology*; D018106:CD28 Antigens / Q000276:immunology; D060908:CTLA-4 Antigen; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology*; D018796:Immunoconjugates; D008213:Lymphocyte Activation / Q000187:drug effects / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D000893:Anti-Inflammatory Agents; D015703:Antigens, CD; D000943:Antigens, Differentiation; D018106:CD28 Antigens; D060908:CTLA-4 Antigen; C556707:Ctla4 protein, mouse; D018796:Immunoconjugates; D000069594:Abatacept; D003907:Dexamethasone