Effect of α_L cross-linking on the movement of CLL and normal B cells on VCAM-1. CLL (A) or normal B cells (B) were preincubated with ICAM-1 complexes (see “Patients, materials, and methods”) to cross-link α_L. Cells were then filmed by TLVM during culture for 60 minutes on VCAM-1- and CCL21-coated plates.