The kinetics of two-dimensional TCR and pMHC interactions determine T-cell responsiveness

Abstract

Studies of the interaction between T-cell receptors (TCRs) and the peptide-major histocompatibility complex (pMHC), which is central to discrimination between pathogens and self antigens, have generally involved 'three-dimensional' analysis, with one of the interacting partners in solution. The resulting kinetic data have not adequately recorded the T-cell response. In reality TCR–pMHC interactions occur in two dimensions, at points of contact between two cells. Here Huang et al. show that two-dimensional TCR–pMHC-binding parameters accurately match the extent of the T-cell response. Quantification of the interaction of T-cell receptors with their peptide–MHC ligands in two–dimensional membranes is shown to yield larger dissociation rate constants than previous assays where one of the interacting partners was in solution. The T-cell receptor (TCR) interacts with peptide-major histocompatibility complexes (pMHC) to discriminate pathogens from self-antigens and trigger adaptive immune responses. Direct physical contact is required between the T cell and the antigen-presenting cell for cross-junctional binding where the TCR and pMHC are anchored on two-dimensional (2D) membranes of the apposing cells1. Despite their 2D nature, TCR–pMHC binding kinetics have only been analysed three-dimensionally (3D) with a varying degree of correlation with the T-cell responsiveness2,3,4. Here we use two mechanical assays5,6 to show high 2D affinities between a TCR and its antigenic pMHC driven by rapid on-rates. Compared to their 3D counterparts, 2D affinities and on-rates of the TCR for a panel of pMHC ligands possess far broader dynamic ranges that match that of their corresponding T-cell responses. The best 3D predictor of response is the off-rate, with agonist pMHC dissociating the slowest2,3,4. In contrast, 2D off-rates are up to 8,300-fold faster, with the agonist pMHC dissociating the fastest. Our 2D data suggest rapid antigen sampling by T cells and serial engagement of a few agonist pMHCs by TCRs in a large self pMHC background. Thus, the cellular environment amplifies the intrinsic TCR–pMHC binding to generate broad affinities and rapid kinetics that determine T-cell responsiveness.