Impaired spreading in the absence of WASP.

B cells from WASP⁻ (▪) and WASP⁺ (■) mice were cultured with indicated stimuli for 46 to 50 hours and were thereafter transferred to anti-CD44–coated plates. Cells were incubated for 17 to 19 more hours and fixed. The frequency of spread cells, having at least one protrusion longer than one cell diameter, was determined. Mean values of 5 samples (LPS and LPS plus IL-4) or triplicate experiments (anti-CD40 mAb, 30 μg/mL) in each group are presented. Error bars represent 1 SD, and at least 300 cells were counted in each group. Brackets indicate P < .001 using a 2-tailed t test. This observation is representative of 3 similar experiments.