Coengagement of VLA-4 slows F-actin flow and attenuates LFA-1 activation. (A and B) T lymphoblasts expressing Lifeact-GFP were imaged while interacting with coverslips coated with anti-CD3, ICAM-1, and VCAM-1. (A) Single time point of a responding cell, and (B) corresponding kymograph of F-actin dynamics generated along the dashed line in A. Bar,10 µm. Arrowhead in B indicates a mobile fiducial mark. (C) Kymographic analysis of F-actin dynamics (817 measurements from 11 cells) superimposed with the normalized radial distribution of F-actin intensity in the same cells. Data represent mean ± SEM. (D) T cells spreading on coverslips coated with anti-CD3 and ICAM-1+/− VCAM-1 were labeled with the indicated antibodies and analyzed for fluorescence intensity in the IS plane. Results represent mean ± SEM from one of three independent experiments. ***, P < 0.001.