Migration toward CCL21 is enhanced after ZAP-70 activation. (A) Ramos transfectants either stimulated (6 hours, 5 μg/mL F(ab′)₂ anti-IgM) or unstimulated, and (B) Raji transfectants were subjected to migration assay toward CCL21 (1 μg/mL) for 15 hours at 37°C in 5% CO₂ atmosphere. The absolute number of transmigrated cells was determined by flow cytometry, acquiring cells under a defined flow rate. Results are expressed as migration index, calculated as the number of cells transmigrating with chemokine divided by the number of transmigrating cells toward media only. ZAP-70–activated cells showed a significantly higher migrative capacity. *P < .05. (C) Peripheral blood mononuclear cells from 7 patients with CLL were subjected to migration assay toward CCL21 (1 μg/mL) for 6 hours at 37°C in 5% CO₂ atmosphere. The percentage of CD19⁺/CD5⁺ CLL cells expressing ZAP-70 was determined in the cellular fraction remaining in the upper chamber and in the cellular fraction of transmigrated cells for each patient sample by flow cytometry. CLL cells transmigrating toward CCL21 after 6 hours had a significantly higher percentage of ZAP-70–positive cells (P = .018).