title: Regulation of CD28 expression on CD8+ T cells by CTLA-4.
abstract: CD28 and CTLA-4 are the critical costimulatory receptors that predominantly determine the outcome of T cell stimulation, with CD28 promoting positive costimulation and CTLA-4 inducing inhibitory signals. Blockage of the B7-CD28/CTLA-4 pathway leads to transplantation tolerance. However, the exact mechanism of the inhibitory function of CTLA-4 remains elusive. Here, we investigated the influence of CTLA-4 expression on CD28 using CTLA-4-transfected Jurkat T cells as well as primary T cells. Up-regulation of CTLA-4 induced abrogation of IL-2 production, indicating an anergic phenotype of CTLA-4(high) T cells. Besides the negative signaling function of CTLA-4, we show for the first time that CTLA-4 expression promotes the down-regulation of CD28 on the T cell surface as a result of enhanced internalization and degradation of CD28. These data suggest that apart from the established competition for B7.1 and B7.2 by CTLA-4, inhibition of T cells by CTLA-4 might be additionally explained by reduction of CD28 on the cell surface, which might impede T cell response to stimulation. Our data provide a previously unrecognized mechanism for T cell regulation.
authors.affiliation: Department of Internal Medicine, University of Iowa Hospitals and Clinics and VA Medical Center, Iowa City, IA 52242, USA.
authors.forename: Martina
authors.initials: M
authors.lastname: Berg
authors.forename: Nicholas
authors.initials: N
authors.lastname: Zavazava
mesh_terms: D015703:Antigens, CD / Q000235:genetics / Q000502:physiology*; D000943:Antigens, Differentiation / Q000235:genetics / Q000502:physiology*; D018106:CD28 Antigens / Q000235:genetics*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D060908:CTLA-4 Antigen; D017931:DNA Primers; D004734:Energy Metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000276:immunology*; D006801:Humans; D007376:Interleukin-2 / Q000032:analysis; D019169:Jurkat Cells; D012016:Reference Values; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013601:T-Lymphocytes / Q000276:immunology*; D014162:Transfection
chemical_list: D015703:Antigens, CD; D000943:Antigens, Differentiation; D018106:CD28 Antigens; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; D017931:DNA Primers; D007376:Interleukin-2