Initiation of TCR Phosphorylation and Signal Transduction. (106.50)

Abstract

Abstract 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 very early molecular events occurring at the immune synapse. The lipid bilayer technology mimics the signaling environment for T cell activation as determined 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 are currently working on elucidating the proposed different roles of unbound and coreceptor associated Lck during the early stages of antigen recognition.