THE VALUE OF FLOW CYTOMETRIC ANALYSIS OF PLATELET GLYCOPROTEIN EXPRESSION ON CD34(-SELECTIN-MEDIATED BINDING OF PLATELETS() CELLS MEASURED UNDER CONDITIONS THAT PREVENT P)

In the present study, we show by adhesion assays and ultrastructural s tudies that platelets can bind to CD34(+) cells from human blood and b one marrow and that this interaction interferes with the accurate dete ction of endogenously expressed platelet glycoproteins (GPs), The inte raction between these cells was found to be reversible, dependent on d ivalent cations, and mediated by P-selectin. Enzymatic characterizatio n showed the involvement of sialic acid residues, protein(s) containin g O-linked glycans, and elastase-sensitive protein(s). The demonstrati on of mRNA for the P-selectin glycoprotein ligand 1 (PSGL-1) in the CD 34(+) cells by polymerase chain reaction (PCR) analysis suggests that this molecule is present in these cells. Under conditions that prevent platelet adhesion, a small but distinct subpopulation of CD34(+) cell s diffusely expressed the platelet GPIIb/IIIa complex. These cells wer e visualized by immunochemical studies. Furthermore, synthesis of mRNA for GPIIb and GPIIIa by CD34(+) cells was shown using PCR analysis. T he semiquantitative PCR results show relatively higher amounts of GPII b mRNA than of PF4 mRNA in CD34(+)CD41(+) cells in comparison with thi s ratio in platelets. This finding is a strong indication that the PCR results are not caused by contaminating adhering platelets. MoAbs aga inst GPIa, GPIb alpha, GPV, P-selectin, and the alpha-chain of the vit ronectin receptor did not react with CD34(+) cells, The number of CD34 (+) cells expressing GPIIb/IIIa present in peripheral blood stem cell (PBSC) transplants was determined and was correlated with platelet rec overy after intensive chemotherapy in 27 patients. The number of CD34( +)CD41(+) cells correlated significantly better with the time to plate let recovery after PBSC transplantation (r = -.83, P = .04) than did t he total number of CD34(+) cells (r = -.55). Statistical analysis prod uced a threshold value for rapid platelet recovery of 0.34 x 10(6) CD3 4(+)CD41(+) cells/kg. This study suggests that if performed in the pre sence of EDTA the flow cytometric measurement of GPIIb/IIIa on CD34(+) cells provides the most accurate indication of the platelet reconstit utive capacity of the PBSC transplant. (C) 1995 by The American Societ y of Hematology.