Recognition of antigen by the T cell receptor (TCR) is the key event for the T cell activation. The earliest molecular events in T cell recognition have not yet been fully described, and the TCR triggering mechanism remains a subject of controversy. By using supported lipid bilayers to present peptide MHC class I complexes to CD8+ cells, we can monitor the molecular events occurring at the immune synapse. The lipid bilayer technology mimics the signaling environment for T cell activation as judged by Ca2+ flux, total phospho-Tyr levels, and IL-2 secretion. Using TIRF/FRET microscopy we have observed an early (> 1 min) interaction between CD3ζ and the coreceptor CD8 that is independent of the MHC-CD8 binding, but requires CD8 association with Lck. Later (< 10 min) CD3ζ-CD8 interactions require CD8-MHC binding. This suggests that, upon antigen recognition, TCR may be initially phosphorylated by Lck not associated with coreceptor, followed by MHC dependent recruitment of CD8-Lck complexes. We have now additional evidences that free Lck is the responsible for the initial TCR phosphorylation. We are currently working on elucidating the proposed different roles of unbound and coreceptor associated Lck during the early stages of antigen recognition.
- Copyright © 2013 by The American Association of Immunologists, Inc.