PECAM-1^−/− MKs show defective bone marrow sinusoidal colocalization 48 hours after platelet depletion. (A) Longitudinal sections of whole murine femora from undepleted PECAM-1^+/+ (i-iii) versus PECAM-1^−/− (iv-vi) mice 48 hours after platelet depletion (vii-ix and x-xii, respectively). MKs were identified by FITC-CD41 (i, iv, vii, x); marrow sinusoidal vessels were identified by CD105/biotin/PE-streptavidin (ii, v, viii, xi); merged images allow comparison of MK location from vessels (iii, vi, ix, xii); yellow color and white arrows show colocalization. Scale bar = 30 μm. (B) The average number of MKs (i) and blood vessels (ii) per field were determined in CD41 and CD105 stained marrow sections throughout the length of 3 femora. *P < .05. Error bars indicate standard error. Images were obtained as described for Figure 2C.