Glycoprotein IIb-IIIa and glycoprotein IV expression on Bernard-Soulier syndrome platelets.

We have read with interest the article by Kunishima et all in which they report a new molecular variant of Bernard-Soulier syndrome (BSS). Kunishima et al' report a patient with a mean platelet volume of 14.7 pm'. Later in the text, they describe binding levels of monoclonal antibody (MoAb) anti-glycoprotein (GP) IIb-IIIa comparable to the control, as measured by flow cytometric techniques. One expects that a larger mean platelet volume should result in an increased surface area on platelets and thus in increased expression of glycoproteins normally present on platelet surface. We have access to a BSS patient2 with an increased mean platelet volume (15.9 pm') in whom the binding of MoAb anti-GP IIb-IIIa (CD4la) was markedly increased with respect to normal controls. Moreover, a parallel increase in the binding of anti-GP IV (CD36) on platelet membrane was also found. Platelet membrane mean fluorescence intensity (in arbitrary units) was for anti-CD4la 195 ? S2 in normal controls (mean t SD, n = S) and 440 in the BSS patient, whereas for anti-CD36 it was 156 ? 45 (mean 2 SD, n = S) in normal controls and 450 in the BSS patient (Fig 1). Our data indicate a consistent increase in the presence of both GP IIb-IIIa and GP IV on abnormally large platelets. These findings are perfectly compatible with normal density of those glycoproteins if we take into consideration the larger surface area of BSS. Our study was performed in whole blood collected in citrate phosphate dextrose (citrate final concentration, 119 nmoVL) with paraformaldehyde (final concentration, 0.3%). Immunolabeling of platelets with conjugated MoAbs (Immunotech, Marseille, France) was performed in whole blood using dual-color analysis.' Fluorescence bound to platelets was analyzed in a FACScan (Becton Dickinson, Mountain View, CA). We wonder whether these discrepancies could be caused by the different techniques used. Kunishima et al' used an indirect staining method in which they first had to obtain plateletrich plasma. It is possible that the bigger platelets could be spun down with red blood cells and that only those with a smaller size remained in the supernatant. In our opinion, direct fluorescence methods applied to BSS patients' whole anticoagulated blood circumvent most of the inconveniences caused by selective sedimentation of the largest platelets, a problem that might have affected the experiments previously referred to.'