AUTHOR=van den Berg Hugo A., Ladell Kristin , Miners Kelly , Laugel Bruno , Llewellyn-Lacey Sian , Clement Mathew , Cole David K., Gostick Emma , Wooldridge Linda , Sewell Andrew K., Bridgeman John S., Price David A. TITLE=Cellular-Level Versus Receptor-Level Response Threshold Hierarchies in T-Cell Activation JOURNAL=Frontiers in Immunology VOLUME=4 YEAR=2013 URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2013.00250 DOI=10.3389/fimmu.2013.00250 ISSN=1664-3224 ABSTRACT=

Peptide-MHC (pMHC) ligand engagement by T-cell receptors (TCRs) elicits a variety of cellular responses, some of which require substantially more TCR-mediated stimulation than others. This threshold hierarchy could reside at the receptor level, where different response pathways branch off at different stages of the TCR/CD3 triggering cascade, or at the cellular level, where the cumulative TCR signal registered by the T-cell is compared to different threshold values. Alternatively, dual-level thresholds could exist. In this study, we show that the cellular hypothesis provides the most parsimonious explanation consistent with data obtained from an in-depth analysis of distinct functional responses elicited in a clonal T-cell system by a spectrum of biophysically defined altered peptide ligands across a range of concentrations. Further, we derive a mathematical model that describes how ligand density, affinity, and off-rate all affect signaling in distinct ways. However, under the kinetic regime prevailing in the experiments reported here, the TCR/pMHC class I (pMHCI) dissociation rate was found to be the main governing factor. The CD8 coreceptor modulated the TCR/pMHCI interaction and altered peptide ligand potency. Collectively, these findings elucidate the relationship between TCR/pMHCI kinetics and cellular function, thereby providing an integrated mechanistic understanding of T-cell response profiles.