Coexpression of von Willebrand factor (VWF) and of GPIIb/IIIa by marrow MKs. The megakaryocytes were simultaneously labeled with fluoresceinated-MoAb to VWF and PE-labeled MoAb to the lineage-specific GPIIb/IIIa complex (CD41a) and stained with 7AAD for measurement of cell DNA content. The megakaryocytic cells are highly resolved from the general marrow cell population by virtue of their distinct expression level. (A) Resolution of marrow MKs by expression of GPIIb/IIIa. (B) Resolution of MKs by the expression of VWF. Small (2N/4N) MKs express a high level of VWF relative to that of the more mature 16N MKs (ratio = 0.5), as compared with the relative expression of GPIIb/IIIa in the same cell populations (ratio = 0.2). Thus, the expression of VWF is a sensitive marker for identification of young marrow MKs.