Inside the microcluster: antigen receptor signalling viewed with molecular imaging tools.

Over the last decade, live cell imaging has revealed the surprisingly complex orchestration of antigen receptor signalling at the immunological synapse. The imaging studies showed that one of the earliest steps in antigen receptor activation is the formation of submicroscopic clusters, which regulate the early signalling events. However, the molecular mechanisms operating inside these microclusters have remained beyond the resolution of optical microscopy. Recent development of imaging techniques that approach molecular resolution in intact cells offers a first view of the molecular processes inside these structures. Here I review the contributions of molecular imaging of the immunological synapse to our understanding of antigen receptor clustering, binding to antigens, and recruitment of signalling molecules. Finally, I provide an outlook on the future prospects of this rapidly advancing technology.