PECAM-1 null CD41a⁺ cells showed abnormal adherence and transmigration behavior. (A) Adherence of WT and CD31KO CD41a⁺ cells on fibronectin- or VCAM-1-coated multiwell plates in the presence or absence of FGF4 (n = 3; P > .04). (B) Integrin α5, αV, β1, and β3 expression profiles were near identical between WT and KO CD41a⁺ cells. Bone marrow cells were harvested for FACS analyses, and only CD41a⁺ cells were gated for integrin expression level quantitation (control = isotype control antibody). (C) Transmigration of WT, Het, and KO littermate CD41a⁺ cells through stromal cell monolayers in response to SDF-1 (400 ng/mL) stimulation (n = 3). (D) CD31KO CD41a⁺ cells showed no defects in CXCR4 expression level. WT and CD31KO bone marrow cells were harvested and cultured for 3 days in Tpo-containing medium. The cells were then analyzed by flow cytometry for CXCR4 expression level on a gated CD41a⁺ cell population. (E) The adherence of WT and CD31KO CD41a⁺ cells on endothelial cell monolayers (n = 3). (F) Transendothelial migration of WT and CD31KO CD41a⁺ cells in response to different dosages of SDF-1 stimulation (n = 3). Vertical lines represent standard deviations.