Movie S1.

Fraction of bound TCR by single-molecule imaging. Contact between single T cells and the supported membrane, presenting fluorescent MCC-MHC and ICAM, is detected by RICM. Ligand molecules under the cell are detected by a short exposure (pMHC, cyan circles). Ligated receptors are detected by a long exposure (pMHC:TCR, magenta circles). The fraction of bound receptors is the ratio of pMHC:TCR/pMHC at every frame. Playback is ∼39 times real time. (Scale bar, 10 μm.)