title: CTLA-4 (CD152) can inhibit T cell activation by two different mechanisms depending on its level of cell surface expression.
abstract: CTLA-4 (CD152) engagement results in down-regulation of T cell activation. Two mechanisms have been postulated to explain CTLA-4 inhibition of T cell activation: negative signaling and competitive antagonism of CD28:B7-mediated costimulation. We assessed the contributions of these two mechanisms using a panel of T cell lines expressing human CTLA-4 with mutations in the cytoplasmic region. Under conditions of B7-independent costimulation, inhibition of IL-2 production following CTLA-4 engagement required the CTLA-4 cytoplasmic region. In contrast, under B7-dependent costimulation, inhibition of IL-2 production by CTLA-4 engagement was directly proportional to CTLA-4 cell surface levels and did not require its cytoplasmic region. Thus, CTLA-4 down-regulates T cell activation by two different mechanisms-delivery of a negative signal or B7 sequestration-that are operational depending on the levels of CTLA-4 surface expression. These two mechanisms may have distinct functional outcomes: rapid inhibition of T cell activation or induction of T cell anergy.
authors.affiliation: Genetics Institute, Inc., Cambridge, MA 02140, USA.
authors.forename: B M
authors.initials: BM
authors.lastname: Carreno
authors.forename: F
authors.initials: F
authors.lastname: Bennett
authors.forename: T A
authors.initials: TA
authors.lastname: Chau
authors.forename: V
authors.initials: V
authors.lastname: Ling
authors.forename: D
authors.initials: D
authors.lastname: Luxenberg
authors.forename: J
authors.initials: J
authors.lastname: Jussif
authors.forename: M L
authors.initials: ML
authors.lastname: Baroja
authors.forename: J
authors.initials: J
authors.lastname: Madrenas
mesh_terms: D000069594:Abatacept; D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D015703:Antigens, CD / Q000276:immunology; D000943:Antigens, Differentiation / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology* / Q000502:physiology; D018122:B7-1 Antigen / Q000502:physiology; D051940:B7-2 Antigen; D018106:CD28 Antigens / Q000276:immunology; D017252:CD3 Complex / Q000276:immunology; D060908:CTLA-4 Antigen; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D003593:Cytoplasm / Q000276:immunology; D015536:Down-Regulation / Q000276:immunology; D004318:Doxycycline / Q000494:pharmacology; D006801:Humans; D018796:Immunoconjugates; D007141:Immunoglobulin Fc Fragments / Q000235:genetics / Q000502:physiology; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D007376:Interleukin-2 / Q000096:biosynthesis; D019169:Jurkat Cells; D008213:Lymphocyte Activation / Q000187:drug effects / Q000276:immunology*; D008562:Membrane Glycoproteins / Q000276:immunology; D008863:Microspheres; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000276:immunology; D011993:Recombinant Fusion Proteins / Q000276:immunology / Q000494:pharmacology; D015398:Signal Transduction / Q000276:immunology; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000943:Antigens, Differentiation; D018122:B7-1 Antigen; D051940:B7-2 Antigen; D018106:CD28 Antigens; D017252:CD3 Complex; C497964:CD86 protein, human; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; D018796:Immunoconjugates; D007141:Immunoglobulin Fc Fragments; D007166:Immunosuppressive Agents; D007376:Interleukin-2; D008562:Membrane Glycoproteins; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D000069594:Abatacept; D004318:Doxycycline