Abstract

The T cell immune response is initiated when the major histocompatibility complex (MHC) protein on the surface of an antigen-presenting cell (APC) interacts with the T-cell receptor (TCR) on a T lymphocyte. We are attempting to understand the initial events in signal propagation using a reductionist approach. In cells, we have replaced the normal T cell receptor with a “chimeric” receptor that can be engineered to study how variations in ligand binding affinity are transduced into intracellular signals. We also have been reconstituting biochemical reactions in the signalling pathway. With ~12 purified proteins or protein complexes, we have been able to reconstitute the signalling pathway from TCR phosphorylation to the nucleation of actin polymerization on planar lipid bilayers. This work illustrates how biochemical reconstitution combined with light microscopy can be used to dissect the biochemical network that underlies the T cell signalling cascade.