Morphology and motility of developing B cells during BM egress. (A) Distribution of B lineage (Rag1^GFP/+) cells in BM of Mb1^Cre/+ Rosa26^+/+ mice (WT, left), Mb1^Cre/+ Rosa26^PTX/+ mice (PTX, middle), and Mb1^Cre/+ Cxcr4^Fl/− mice (X4^Δ, right). Dotted lines indicate border between sinusoids and parenchyma. (B) Ratio of B lineage cells proximal (<10 µm) and distal (>10 µm) to BM sinusoids. Data depicted were from >90 B lineage cells analyzed in three WT, PTX, and X4^Δ mice. Bars indicate mean (±SEM). (C–E) Cell motility parameters of developing B cells in parenchyma and in perisinusoidal space. (C) Median velocity (µm/min). (D) Mean motility coefficient of Rag1^GFP/+ B lineage cells in inner parenchyma (Inner Par. blue) and in perisinusoidal areas (Per. red). Mean cell displacement from starting coordinates is plotted against the square root of time. Lines depict the average mean motility coefficient of >70 inner parenchyma and 40 perisinusoidal areas GFP⁺ B cells. (E) Axis ratio (x/y). Dotted line depicts the mean axis ratio of Mb1^Cre/+ Rosa26^PTX/+ B cells in BM parenchyma (1.2). (C and E) Lines indicate means. (F and G) Two WT GFP⁺ B cells (F) and one PTX-expressing GFP⁺ B cell (G) exiting from BM parenchyma (P) into sinusoids (S). Arrowheads point to cell egress. Time is shown in mm:ss. WT and PTX-expressing cell egress examples were captured from more than 10 and 4 independent experiments, respectively. Bars: (A) 19 µm; (F and G) 5 µm. *, P < 0.05; **, P < 0.005 by unpaired Student’s t test. Unpaired Student’s t test with Welch’s correction was used in E.