On average, TCR MCs reside between arcs, whereas active LFA-1 coincides with arcs in maturing synapses. (A) Three-color 3D-SIM imaging of endogenous actin (grayscale), TCR MCs (red), and open, active LFA-1 (green) at a Jurkat T cell IS 6 min after bilayer engagement. (A, bottom nine panels) Pairwise comparisons of the actin, LFA-1, and TCR MC channels and overlays. (B) Pearson’s correlation coefficient; n = 20–40 cells/correlation. Box plots are centered on means and display upper and lower quartile ranges and min to max values. (C) Line scans across population-averaged TCR MCs. n = 110. (D) Radial plot profiles of population-averaged TCR MCs. n = 11 cells; 10–15 TCR MCs/cell. Data are means ± SEM. Note that TCR MCs overlap considerably with F-actin during initial cell spreading (Lam Hui et al., 2014). Bars, 1 µm. ****, P < 0.0001. a.u., arbitrary units; MyoIIA, myosin IIA; Norm. Fluor. Int., normalized fluorescence intensity.