Dependence of T Cell Antigen Recognition on T Cell Receptor-Peptide MHC Confinement Time

Abstract

SummaryT cell receptor (TCR) binding to diverse peptide-major histocompatibility complex (pMHC) ligands results in various degrees of T cell activation. Here we analyze which binding properties of the TCR-pMHC interaction are responsible for this variation in pMHC activation potency. We have analyzed activation of the 1G4 cytotoxic T lymphocyte clone by cognate pMHC variants and performed thorough correlation analysis of T cell activation with 1G4 TCR-pMHC binding properties measured in solution. We found that both the on rate (kon) and off rate (koff) contribute to activation potency. Based on our results, we propose a model in which rapid TCR rebinding to the same pMHC after chemical dissociation increases the effective half-life or “confinement time” of a TCR-pMHC interaction. This confinement time model clarifies the role of kon in T cell activation and reconciles apparently contradictory reports on the role of TCR-pMHC binding kinetics and affinity in T cell activation.

Architecture of a minimal signaling pathway explains the T-cell response to a 1 million-fold variation in antigen affinity and dose

“…First, the dose-response seemed to exhibit a bell shape with reduced cytokine production at high pMHC concentrations. This bell shape was less pronounced or absent for low-affinity ligands, which is consistent with published studies reporting a sigmoidal dose-response for low-affinity ligands (14,15,17,18,21,23,41). Second, the peak amplitude of the bell-shaped dose-response was similar for pMHCs despite large differences in their affinities.…”

“…Purified pMHC was biotinylated in vitro by BirA enzyme (Avidity). The α and β subunits of the c58c61 (Clone 113) high-affinity 1G4 T-cell receptor (27) were expressed in E. coli as inclusion bodies, refolded in vitro, and purified using size-exclusion chromatography as described previously (17).…”

“…TCR-pMHC binding affinity and kinetics were measured by surface plasmon resonance using a Biacore 3000 (GE Healthcare) as previously described (17). Briefly, biotinylated pMHCs were coupled to the CM5 surface by covalently coupled streptavidin with a target immobilization level of 250 response units (RU) to minimize mass transport effects.…”

“…Studies performed over the last two decades have focused on empirically mapping the relationship between pMHC affinity and T-cell activation (5,(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24). A number of studies have reported an optimal pMHC affinity for T-cell activation, but other studies have failed to observe the optimum.…”

Phenotypic models of T cell activation

“…The implication of this for the TCR is that intervals between rebinding events may not be detected and therefore the effective 2D dissociation time is approximately equal to the 3D dissociation time multiplied by the number of rebinding events 15,82,83 . As the number of rebinding events is determined, in part, by the on-rate (k on ), the 2D dissociation time may exhibit a dependency on k on .…”