Single-molecule microscopy reveals heterogeneous dynamics of lipid raft components upon TCR engagement.

The existence of lipid rafts and their importance for immunoreceptor signaling is highly debated. By non-invasive single molecule imaging, we analyzed the dynamics of the T-cell antigen receptor (TCR), the lipid raft-associated glycosylphosphatidylinositol (GPI) proteins CD48 and CD59 and the major leukocyte phosphatase CD45 in living naive T lymphocytes. TCR triggering induced the immobilization of CD45 and CD48 at different positions within the T-cell interface. The second GPI protein, CD59, did not co-immobilize indicating lipid raft heterogeneity in living T lymphocytes. A novel biochemical approach confirmed that lipid raft components are not associated in the plasma membrane of resting cells, and variably associate with specific receptors to distinct lipid rafts upon activation.