c-Abl is required to organize TCR-induced lamellipodial protrusions. Jurkat T cells stably expressing GFP-actin were transfected with control vector (A) or shAbl-3 (B). Actin dynamics were monitored by video confocal microscopy as the cells spread on anti-TCR–coated coverslips. Selected time-lapse image projections acquired at the indicated times after contact with the coverslip are shown. (C) The contact area of each cell at each time point was determined, and the average was calculated for each cell population at each 5-second time point (40 cells for control vector, and 26 cells for shAbl-3–transfected cells). The difference in area was statistically significant (P = .005 at 130 seconds).