ICAM-1 engagement retains the pool of activated LFA-1 in the IS periphery. (A and B) T lymphoblasts were allowed to interact with coverslips coated with anti-CD3 and ICAM-1 (A) or anti-CD3 alone (B) for 30 min and analyzed as in Fig. 1. (C and D) T lymphoblasts expressing Lifeact-GFP were imaged live while spreading on coverslips coated with anti-CD3 alone. (C) Single time point of a responding cell and (D) corresponding kymograph of F-actin dynamics generated along the dashed line in C. Arrowhead indicates a mobile fiducial mark in the F-actin network. (E) Kymographic analysis of F-actin flow rates along IS radii (663 measurements from 13 cells) superimposed on the normalized radial distribution of F-actin intensity in the same cells. (F and G) T lymphoblasts expressing Lifeact-GFP were imaged live while interacting with coverslips coated with anti-CD3+ ICAM-1, analyzed as in C–E (1,180 measurements from 21 cells). Data in E and H represent means ± SEM. Bars, 5 µm.