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 examin ed the amount of mpl, glycoprotein IIb/IIIa (gpIIb/IIIa) and glycoprotein I b (gpIb) on platelets from healthy volunteers and patients with refractory anemia (RA). For the analysis of mpl expression, we applied both a non-isot opic ligand binding assay and immunofluorescence using anti-mpl monoclonal antibody, and compared the results from both methods. The non-isotopic liga nd binding assay has been developed in our laboratory and is suitable for t he quantitative analysis of a small amount of cytokine receptors such as mp l on platelets. In platelets from patients with RA, the amount of mpl expre ssed by the D value was 0.05 +/- 0.03 (mean +/- standard deviation), and wa s 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 p latelets 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 goo d correlation between the amount of mpl and the MFI of gpIIb/IIIa (p = 0.79 4, 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 o f mpl as well as a reduced expression of gpIIb/IIIa and gpIb on platelets f rom RA patients.