Defective L-selectin–dependent adhesion of WASp^I294T cells under flow conditions. 300.19 pre-B cells expressing either EGFP (SEW), WASp^WT, or WASp^I294T were perfused over immobilized sLe^x in flow chambers. Conditions were optimized for cell rolling (2.5 dyne/cm²). (A) Dramatic reduction in the number of cells rolling per field of view in cells expressing WASp^I294T compared with WASp^WT or EGFP-expressing cells (SEW). (B) Average rolling velocity was significantly increased in cells expressing WASp^I294T. All error bars represent SD. (C) Compared with WASp^WT cells, WASp^I294 cells demonstrated a jerky rolling behavior characterized by an increase in velocity fluctuation over time. These profiles are comparable with the data presented in Figure 2C. Rolling assays in panels A and B were compiled from 3 independent experiments. The superimposed line represents a velocity of 200 μm/second, which is the velocity threshold above which cells are normally considered to be in free flow.