Activation induced decrease and recovery of TCR 2D affinity and bond lifetime

Abstract Shortly after encountering antigen, T cells are considered transiently unresponsive or refractory to subsequent simulation. To determine whether antigen stimulation also changes the cell surface biophysical interaction between TCR and pMHC, we assessed the 2D TCR affinity and bond lifetime under force between this receptor ligand pair. Virus (LCMV) specific SMARTA transgenic CD4+ T cells were stimulated with peptide in vitro and 2D TCR affinity and bond lifetime determined at various time points after stimulation using the 2D micropipette adhesion frequency assay and the biomembrane force probe (BFP) respectively. We found activated T cells downregulated 2D affinity at twelve and twenty-four hours after seeing antigen with affinity recovering to naïve levels by forty-eight hours. Unlike pMHC tetramer staining which was dependent on TCR expression levels, the decrease in affinity was independent of antigen dose and degree of TCR downregulation. TCR:pMHC bond lifetime under force was also reduced early after antigen encounter with a steady recovery observed with time. Our data demonstrate a decrease in bond lifetime and relative 2D affinity of TCR and pMHC result from early T cell activation events followed by a recovery phase with both changes occurring independent of activation induced modulation of TCR expression. Thus, TCR affinity for pMHC is dynamic in the 2D T cell membrane context with cellular events allowing the T cell to fine-tune the ability of TCR to interact with antigen.