title: Differential effects of CD28 engagement and IL-12 on T cell activation by altered peptide ligands.
abstract: To futher our understanding of the mechanisms underlying the diverse effects of altered peptide ligands (APL) on T cell activation, we used a population of nonactivated spleen cells from mice that expressed a transgenic TCR specific for myelin basic protein Ac1-11 and peptide analogues that display either enhanced or decreased affinities for TCR/MHC to address the question whether APL-induced signaling through the TCR can regulate the capability of APC to activate T cells. We demonstrate that weak agonists APL are poor inducers of all aspects of the activation of both the responder T cells and the APC. Enhancement of the antigenic signal by augmenting the binding of the weak agonists to MHC reversed their defective activating capacity. Enhancement of costimulation by engagement of CD28 only resulted in augmentation of the capacity of the weak agonist APL to induce proliferation and IL-2/IL-3 production, but not CD40L or IL-12Rbeta2 chain expression on T cells, CD80/CD86 expression on APC, IL-12 secretion, or IFN-gamma production. Exogenous IL-12 promoted IFN-gamma production in the presence of the weak agonists. These studies demonstrate that there is a critical threshold of antigenic signal required for full activation of the T cell-APC interactions needed for the differentiation of Th1 cells. The provision of excess costimulation can overcome some of the defects in T cell activation by weak agonists, but is insufficient to induce a sufficient level of CD40L expression needed for engagement of CD40 on APC with subsequent IL-12 production and induction of IL-12Rbeta2 chain expression.
authors.affiliation: Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892-1892, USA.
authors.forename: L
authors.initials: L
authors.lastname: Ding
authors.forename: E M
authors.initials: EM
authors.lastname: Shevach
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D017951:Antigen Presentation; D015703:Antigens, CD / Q000096:biosynthesis / Q000235:genetics; D018122:B7-1 Antigen / Q000096:biosynthesis / Q000235:genetics; D051940:B7-2 Antigen; D018106:CD28 Antigens / Q000276:immunology*; D023201:CD40 Ligand; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D006183:H-2 Antigens / Q000276:immunology; D007371:Interferon-gamma / Q000096:biosynthesis / Q000235:genetics; D018664:Interleukin-12 / Q000378:metabolism / Q000494:pharmacology*; D008024:Ligands; D008213:Lymphocyte Activation / Q000187:drug effects*; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D004676:Myelin Basic Protein / Q000737:chemistry / Q000276:immunology; D010446:Peptide Fragments / Q000737:chemistry / Q000276:immunology*; D011485:Protein Binding; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000235:genetics / Q000276:immunology*; D018123:Receptors, Interleukin / Q000096:biosynthesis / Q000235:genetics; D053707:Receptors, Interleukin-12; D015398:Signal Transduction; D013047:Specific Pathogen-Free Organisms; D013154:Spleen / Q000166:cytology; D013379:Substrate Specificity; D013601:T-Lymphocytes / Q000187:drug effects* / Q000276:immunology
chemical_list: D015703:Antigens, CD; D018122:B7-1 Antigen; D051940:B7-2 Antigen; D018106:CD28 Antigens; C497965:Cd86 protein, mouse; D006183:H-2 Antigens; D008024:Ligands; D008562:Membrane Glycoproteins; D004676:Myelin Basic Protein; D010446:Peptide Fragments; D016693:Receptors, Antigen, T-Cell, alpha-beta; D018123:Receptors, Interleukin; D053707:Receptors, Interleukin-12; D023201:CD40 Ligand; D018664:Interleukin-12; D007371:Interferon-gamma