L-selectin is the key factor controlling the arrest of CLL cells within LN HEVs. (A) Flow cytometry analysis of the expression of L-selectin, LFA-1, and CXCR4 on CD19⁺CD5⁺ CLL cells. Graphs represent the MFIR of CLL cells from patients without (●, n = 7) or with (▪, n = 7) bulky disease. Mean ± SEM are shown. Unpaired t test; *P < .05. (B-D) Calcein-labeled CLL cells from patients were untreated (black) or treated with a function blocking anti-L-selectin Ab (white) or an isotype control Ab (gray). (B) The rolling and sticking fractions of CLL cells from a patient with bulky disease in the indicated venules are shown. Mean ± SD, venular order III (n = 3), order IV (n = 3), order V (n = 5). Unpaired t test; *P < .05; **P < .01. (C) The rolling fractions of CLL cells from 2 other patients with bulky disease and 3 patients with no bulky disease in venular order V are shown. Mean ± SD, venular order V (n = 3). (D) The sticking fractions of CLL cells from 1 representative patient (of 3) with bulky disease (BL18) and no bulky disease (BL11) in venular order V are shown. Mean ± SD, venular order V (n = 3).