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Original Article |
Recent data using MHC/peptide tetramers and dimers suggests that the T cell coreceptors, CD4 and CD8, although important for T cell activation, do not play a direct role in facilitating T cell receptor (TCR) binding to multivalent MHC/peptide ligands. Instead, a current model proposes that coreceptors are recruited only after a stable TCR–MHC/peptide complex has already formed and signaled. In contrast, we show using multimeric class I MHC/peptide ligands that CD8 plays a critical (in some cases obligatory) role in antigen-specific TCR binding. T cell activation, measured by calcium mobilization, was induced by multimeric but not monomeric ligands and also showed CD8 dependency. Our analysis using anti-CD8 antibodies revealed that binding to different epitopes of CD8 can either block or augment TCR–MHC/peptide interaction. These effects on TCR binding to high-affinity agonist ligands were even more pronounced when binding to multimeric low-affinity ligands, including TCR antagonists, was studied. Our data have important implications for the role of CD8 in TCR binding to MHC/peptide ligands and in T cell activation. In addition, our results argue against the view that multimeric MHC/peptide ligands bind directly and solely to the TCR; rather, our data highlight a pivotal contribution of CD8 for this association.
Key Words: MHC/peptide tetramers • T cell activation • cytotoxic T lymphocyte • calcium • flow cytometry
Address correspondence to Stephen C. Jameson, Center for Immunology and Dept. of Lab Medicine and Pathology, University of Minnesota Medical School, Box 334 FUMC, 420 Delaware St. SE, Minneapolis, MN 55455. Phone: 612-625-1496; Fax: 612-625-2199; E-mail: james024@tc.umn.edu
© 2000 The Rockefeller University Press
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