RELATIONSHIP OF MICROPARTICLES WITH BETA(2)-GLYCOPROTEIN-I AND P-SELECTIN POSITIVITY TO ANTICARDIOLIPIN ANTIBODIES IN IMMUNE THROMBOCYTOPENIC PURPURA

We investigated the association of beta(2)-glycoprotein I and P-selectin with platelet-derived microparticles in 48 patients with immune thrombocytopenic purpura and 20 normal controls using two-color flow cytometric analysis. In addition, anticardiolipin antibodies were detected by an enzyme-linked immunosorbent assay. Platelet microparticles from the patients showed a higher positivity for beta(2)-glycoprotein I than those from the normal controls (23.1+/-15.4% vs. 5.3+/-3.1%, p<0.01), but this positivity was not related to the presence of platelet-associated IgG or to the severity of thrombocytopenia. In the 18 patients with more than 20% P-selectin-positive microparticles, beta(2)-glycoprotein I positivity was significantly higher than in the 30 patients with less than 20% P-selectin-positive microparticles (37.1+/-20.5% vs. 21.5+/-17.3%, p<0.01). In addition, anticardiolipin antibodies were detected in eight patients, and they had a significantly higher level of beta(2)-glycoprotein I-positive microparticles than the patients without such antibodies (42.0+/-22.9% vs. 22.6+/-18.9%, p<0.05). Our results suggest that anticardiolipin antibodies activate platelets in immune thrombocytopenic purpura and cause the generation of microparticles rich in beta(2)-glycoprotein I and P-selectin. These microparticles may then act to regulate coagulation abnormalities in patients with anticardiolipin antibodies.