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* Department of Biochemistry, University of Illinois, Urbana, IL 61801; and
Koch Institute for Integrative Cancer Research and Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139
TCR interactions with cognate peptide-MHC (pepMHC) ligands are generally low affinity. This feature, together with the requirement for CD8/CD4 participation, has made it difficult to dissect relationships between TCR-binding parameters and T cell activation. Interpretations are further complicated when comparing different pepMHC, because these can vary greatly in stability. To examine the relationships between TCR-binding properties and T cell responses, in this study we characterized the interactions and activities mediated by a panel of TCRs that differed widely in their binding to the same pepMHC. Monovalent binding of soluble TCR was characterized by surface plasmon resonance, and T cell hybridomas that expressed these TCR, with or without CD8 coexpression, were tested for their binding of monomeric and oligomeric forms of the pepMHC and for subsequent responses (IL-2 release). The binding threshold for eliciting this response in the absence of CD8 (KD = 600 nM) exhibited a relatively sharp cutoff between full activity and no activity, consistent with a switchlike response to pepMHC on APCs. However, when the pepMHC was immobilized (plate bound), T cells with the lowest affinity TCRs (e.g., KD = 30 µM) responded, even in the absence of CD8, indicating that these TCR are signaling competent. Surprisingly, even cells that expressed high-affinity (KD = 16 nM) TCRs along with CD8 were unresponsive to oligomers in solution. The findings suggest that to drive downstream T cell responses, pepMHC must be presented in a form that supports formation of appropriate supramolecular clusters.
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 This work was supported by National Institutes of Health Grants GM55767 and CA097296 (to D.M.K.), a grant from the James S. McDonnell Foundation (to D.M.K.), and National Institutes of Health Grants CA100875 and AI50631 (to J.C.). A.B. was supported in part by the Margaret A. Cunningham Immune Mechanisms in Cancer Research Fellowship and postdoctoral fellowships from the Sorono Foundation and National Institutes of Health. J.D.S. was supported by the Samuel and Ruth Engelberg/Irvington Institute Fellowship of the Cancer Research Institute.
2 A.S.C. and J.D.S. contributed equally to this work.
3 Address correspondence and reprint requests to Dr. David M. Kranz, Department of Biochemistry, University of Illinois, 600 South Mathews Avenue, Urbana, IL 61801. E-mail address: d-kranz{at}uiuc.edu
4 Abbreviations used in this paper: pepMHC, peptide-MHC; PBST, PBS containing 0.05% Tween 20; pERK, phosphorylated ERK; scTCR, single-chain TCR; SPR, surface plasmon resonance; tg, transgenic; WT, wild type; MSCV, murine stem cell virus.
5 The online version of this article contains supplemental material.
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  N. A. Bowerman, L. A. Colf, K. C. Garcia, and D. M. Kranz Different Strategies Adopted by Kb and Ld to Generate T Cell Specificity Directed against Their Respective Bound Peptides J. Biol. Chem., November 20, 2009; 284(47): 32551 - 32561. [Abstract] [Full Text] [PDF]
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