Subcellular localization of CD80 receptors is dependent on an intact cytoplasmic tail and is required for CD28-dependent T cell costimulation.
CD28 provides a major costimulatory signal to T cells when it is cross-linked with mAb, immobilized recombinant ligand (CD80Ig or CD86Ig), or ligand-bearing cells but not when it is bound by specific Fab fragments or monomeric ligand. We wanted to determine how monomeric CD80 could cross-link CD28 since CD80 is expressed as a monomer on the surface of APC. We found that CD80 may interact with the actin-based cytoskeleton. To test whether the interaction of CD80 with the cytochalasin B-sensitive cytoskeleton was necessary for T cell costimulation through CD28, we constructed a tailless form of CD80 and generated stable transfectants of Chinese hamster ovary epithelial cells and Reh B cells expressing either the tailless or wild-type CD80 molecules. Unlike control cells expressing wild-type CD80, the tailless CD80 transfectants expressing equivalent levels of surface CD80 were not able to provide a costimulatory signal for anti-CD3-induced T cell proliferation, up-regulation of CD25 (IL-2Ralpha) expression, or the induction of IL-2 secretion. Thus, the cytoplasmic tail of CD80 apparently is required to signal T cells. Confocal microscopic studies revealed that wild-type CD80 and tailless CD80 have different patterns of subcellular distribution in both epithelial and lymphoid cells. Furthermore, T cell contact induces more patching and capping of CD80 in wild-type CD80-expressing cells than in tailless CD80-expressing cells. This suggests that the cytoplasmic region of CD80 functions to localize CD80 in complexes required for effective T cell costimulation.
Doty
R T
RT
Department of Immunology, University of Washington, Seattle 98195, USA.
Clark
E A
EA
D000818:Animals; D018122:B7-1 Antigen / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D018106:CD28 Antigens / Q000378:metabolism*; D016466:CHO Cells; D002455:Cell Division; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology; D006224:Cricetinae; D003432:Cross-Linking Reagents; D003593:Cytoplasm / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D007152:Immunologic Capping; D008024:Ligands; D008213:Lymphocyte Activation; D013347:Subcellular Fractions / Q000378:metabolism; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology*; D014162:Transfection
D018122:B7-1 Antigen; D018106:CD28 Antigens; D003432:Cross-Linking Reagents; D017931:DNA Primers; D008024:Ligands