Decreased amount of mpl and reduced expression of glycoprotein IIb/IIIa and glycoprotein Ib on platelets from patients with refractory anemia: analysis by a non-isotopic quantitative ligand binding assay and immunofluorescence.

Using a non-isotopic ligand binding assay and immunofluorescence, we examined the amount of mpl, glycoprotein IIb/IIIa (gpIIb/IIIa) and glycoprotein Ib (gpIb) on platelets from healthy volunteers and patients with refractory anemia (RA). For the analysis of mpl expression, we applied both a non-isotopic ligand binding assay and immunofluorescence using anti-mpl monoclonal antibody, and compared the results from both methods. The non-isotopic ligand binding assay has been developed in our laboratory and is suitable for the quantitative analysis of a small amount of cytokine receptors such as mpl on platelets. In platelets from patients with RA, the amount of mpl expressed by the D value was 0.05+/-0.03 (mean+/-standard deviation), and was significantly lower than that in healthy volunteers (0.15+/-0.05, p<0.0001). The mean fluorescence intensities (MFI) of gpIIb/IIIa and gpIb on platelets from RA patients were 28.8+/-8.8 and 20.8+/-7.7, respectively, and were significantly lower than those on normal subjects (93.2+/-22.6 and 67.4+/-9.1, p<0.0001 and p<0.0001, respectively). There was a good correlation between the amount of mpl and the MFI of gpIIb/IIIa (p=0.794, p<0.0001) or gpIb (p=0.774, p<0.0001), and between those of gpIIb/IIIa and gpIb (p=0.728, p<0.0001). We demonstrated a decreased amount of mpl as well as a reduced expression of gpIIb/IIIa and gpIb on platelets from RA patients.