title: Intracellular capture of B7 in antigen-presenting cells reduces costimulatory activity.
abstract: CTLA-4 gene constructs were designed to express CTLA-4 exclusively in the endoplasmic reticulum (ER). Four different CTLA-4 gene constructs were transfected into HEK 293 (human embryonic kidney) and A20 (Balb/c mouse B lymphoma) cells. All constructs contained an ER retention signal and coded for CTLA-4 expression in the ER. One of the constructs, which contained the membrane part of CTLA-4, coded for an expression both on the cell surface and in the ER. Three of the expressed CTLA-4 types (including the ER-membrane-expressed form) caused a reduced surface expression of B7 in the A20 cells. Only constructs which allow dimerization of CTLA-4 showed this effect. It is assumed that intracellular CTLA-4 bound B7 and inhibited therefore the transport of B7 to the surface. The binding obviously caused also an enhanced degradation of the complexes because both proteins showed a low concentration in the transfected cell lines. CTLA-4-transfected and B7-reduced A20 cells showed a diminished costimulating activity upon T cells. This was demonstrated by a reduced proliferation of T cells from ovalbumin-immunized Balb/c mice, incubated with ovalbumin peptide-primed CTLA-4-transfected A20 cells.
authors.affiliation: Genethor GmbH, Robert-Rössle-Str. 10, D-13125, Berlin, Germany. sheriff@mdc-berlin.de
authors.forename: Ahmed
authors.initials: A
authors.lastname: Sheriff
authors.forename: Birgit
authors.initials: B
authors.lastname: Vogt
authors.forename: Martin
authors.initials: M
authors.lastname: Baumgart
authors.forename: Carola
authors.initials: C
authors.lastname: Montag
authors.forename: Birgit
authors.initials: B
authors.lastname: Hollenbach
authors.forename: Jörg A
authors.initials: JA
authors.lastname: Schenk
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Ulrich
authors.forename: Fernando
authors.initials: F
authors.lastname: Elías
authors.forename: Burkhard
authors.initials: B
authors.lastname: Micheel
mesh_terms: D000069594:Abatacept; D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology*; D015703:Antigens, CD / Q000378:metabolism*; D000943:Antigens, Differentiation / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018122:B7-1 Antigen / Q000378:metabolism*; D051940:B7-2 Antigen; D001483:Base Sequence; D016466:CHO Cells; D060908:CTLA-4 Antigen; D002460:Cell Line; D006224:Cricetinae; D018076:DNA, Complementary / Q000235:genetics; D019281:Dimerization; D004721:Endoplasmic Reticulum / Q000276:immunology; D006801:Humans; D018796:Immunoconjugates; D066298:In Vitro Techniques; D008213:Lymphocyte Activation; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D010957:Plasmids / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013601:T-Lymphocytes / Q000276:immunology; D014162:Transfection
chemical_list: D015703:Antigens, CD; D000943:Antigens, Differentiation; D018122:B7-1 Antigen; D051940:B7-2 Antigen; C497964:CD86 protein, human; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; C497965:Cd86 protein, mouse; C556707:Ctla4 protein, mouse; D018076:DNA, Complementary; D018796:Immunoconjugates; D008562:Membrane Glycoproteins; D011994:Recombinant Proteins; D000069594:Abatacept