Biophysical Force on the T-Cell Receptor Fosters Digital Antigen Responsiveness and Exquisite Specificity during T-Cell Activation

Abstract

T-lymphocytes use their surface T-cell receptors (αβTCRs) to recognize sparse antigenic peptides bound to MHC molecules (pMHC) arrayed on antigen presenting cells (APCs). Both T-cell movements and cytoskeletal rearrangements generate force load on TCR-pMHC bonds at the T-cell/APC interface during immunosurveillance. Thus, in contrast to equilibrium models for T-cell activation, physical forces play a crucial role in providing a non-equilibrium mechanosensor-based energizing mechanism. In this thesis, the acquired isolated single molecule and single cell data with optical tweezers directly reveal that a force-dependent, energized structural transition at the T-cell receptor β-subunit allosterically regulates antigenic peptide discrimination and pMHC bond lifetime. Our findings of single T-cell activation show the association of a pMHC triggered-TCR with cytoskeletal elements including a single motor define the importance of anisotropic (i.e. force direction-dependent) activation and characterize initiation of immunological synapse (IS), assessing the veracity of the longstanding serial engagement concept. The mechanical force-induced T-cell activation also drives the reconfiguration and segregation of triggering inhibitors (e.g. CD45), which are akin to a phase transition associated with exchange of energy. The emerging picture incorporating molecular features of the αβTCR mechanome is paragidm shifting relative to earlier T-cell activation models, with significant implications for monitoring and design of CTL-based immunotherapy.