Desperately seeking synapses

Signaling between a T cell and an antigen-presenting cell (APC) is orchestrated through a bull's eye–like structure known as the immunological synapse. But no one had ever spotted these structures in vivo, causing many to wonder whether they are immunology's equivalent of the Loch Ness monster. Synapse devotees can now rest easy, thanks to Barcia et al., who provide the first in vivo glimpse of these elusive cellular structures on page 2095.

When first described, immunological synapses—their centers rich with T cell receptor (TCR)-MHC/peptide complexes and their outer rings with stabilizing integrins and adhesion molecules—provided a satisfying spatial model of how T cells get activated and signal to target APCs. But although these structures formed readily when T cells bumped into artificial lipid bilayers or cultured APCs, they have proven difficult to capture...