Follicular B-cell migration in absence of ICAM-1. (A) Instantaneous 3D velocity of follicular B cells in WT and ICAM-1^−/− PLNs, treated or not with the anti-α4 blocking mAb PS/2. The mean velocity plus or minus SEM is indicated in the top right corner in μm/min. B cells are significantly slower in absence of ICAM-1 (P < .001), and their velocity can be further decreased after treatment with PS/2 (P < .001). (B) Normalized, cumulative meandering indices of B cells migrating in WT and ICAM-1^−/− PLNs, treated or not with the anti-α4 blocking mAb PS/2. (C) Motility coefficients of B cells migrating in WT and ICAM-1^−/− PLNs, treated or not with the anti-α4 blocking mAb PS/2. Absence of ICAM-1 significantly reduces the motility coefficient. n.s. indicates not significant. *P < .05. Data are pooled from 2 to 4 independent experiments yielding 4 to 5 image sequences containing 653, 345, and 340 cell tracks for WT, ICAM-1^−/−, and ICAM-1^−/− + PS/2 PLNs, respectively. (D) Instantaneous 3D velocity (top panels) and change in cell direction distribution (turning angles, bottom panels) of follicular B cells in PLNs of WT and ICAM-1/-2^−/− BM chimeras. For WT→WT BM chimera, 1 mouse per 4 image sequences per 442 cell tracks was analyzed, while for WT→ICAM-1-2^−/− BM chimera, we examined 2 mice per 4 image sequences per 389 tracks.