HVS-immortalized WAS T cells do not polymerize actin in response to stimulation with immobilized anti-CD3 MoAb. HVS-Normal (HVS-N8) and HVS-WAS (HVS-WAS1) cells were stimulated with immobilized anti-CD3 MoAb for indicated times, fixed, permeabilized, stained with Rhodamine-phalloidin, and finally analyzed by flow cytometry. Fluorescence profiles of stimulated (solid figures) and unstimulated (open figures, dotted lines) cells are overlayed. Thus, the negative control is set to represent the total amount of F-actin contained in unstimulated cells. The increase in the fluorescence intensity indicates a rapid passage from G-actin to F-actin in Normal cells in response to OKT3 (central column), a process that is specifically abrogated by pretreatment of cells with cytochalasin D (right column). HVS-WAS cells are unable to polymerize actin in response to OKT3 (left column).