Normal levels of pro-B cells and mature B cells in the bone marrow of PECAM-1^−/− mice.

(A) PECAM-1 is expressed on more than 95% of wild-type C57/BL6 splenic lymphocytes. This expression is completely ablated in PECAM-1 knock-out animals. Spleen cells from PECAM-1^+/+ and PECAM-1^−/− mice were stained with biotinylated antimouse PECAM-1 390 antibody and binding detected with streptavidin–R-PE. Data analyses were performed on an EPICS XL-MCL flow cytometer and confined to the lymphocyte population, as defined by their forward- and side-scatter characteristics. (B,C) Representative scatterplots of bone marrow lymphocytes from 6-week-old PECAM-1^+/+ (n = 15) and PECAM-1^−/− mice (n = 15). Cells were isolated from a single femur, red blood cells were lysed, and the cells were dual stained for (B) pro-B lymphocytes using CD43/B220 and (C) mature B lymphocytes using IgM/IgD.