Actin reorganization of HVS-Normal (HVS-N8 [a through d]) and HVS-WAS (HVS-WAS1 [e through h]) T-cell lines in response to stimulation with immobilized anti-CD3 MoAb. HVS-Normal (a through d) and HVS-WAS (e through h) T cells were stimulated with immobilized OKT3 MoAb for 5 minutes (a and e), 15 minutes (b and f ), and 30 minutes (c and g). In HVS-Normal cells, actin rings are progressively dissolved, followed by cellular spreading and frequent formation of pseudopodia. In contrast, in HVS-WAS T cells, actin rings yield to strongly polarized accumulations of F-actin. HVS-WAS T cells that fail to spread acquire atypical shapes with the appearance of structures resembling uropods. Pretreatment of cells with cytochalasin D abrogates all actin-specific changes in both HVS-Normal (d) and HVS-WAS (h) immortalized T cells. (Original magnification × 400, except for [d] and [h], which are ×630.)