ADynamic View of T Cell Behavior. For many years it has been known that T lymphocytes engage APCs in a long-lasting interaction that results in the generation of a rapid and sustained signal in T cells. Lasting almost 1 h, this sustained signal is required by T cells to maintain the transcription factors translocated in the nucleus and, ultimately, to become activated (1). However, in view of the low number of ligands recognized and of the low affinity of TCR, the question of how T cells maintain the sustained signal and become activated remained a puzzle (2).
Unlike the antigen–antibody interaction that can be easily studied by measuring the proportions of the reactants at equilibrium, the interaction of the TCR with its ligand has proved to be much more difficult to analyze. This interaction occurs in the limited space between the opposing membranes...
