Increased P-selectin plasma levels in patients with thrombotic thrombocytopenic purpura

Background. Thrombotic thrombocytopenic purpura (TTP) is a rare vascular disorder of unknown etiology. There is evidence to support the hypothesis that platelets and endothelium play a pivotal pathogenetic role. Immunological assays for plasma thrombomodulin and P-selectin levels have recently been made available and they allow simple evaluation of endothelial damage and endothelial/platelet activation, respectively. In this study, we measured the plasma levels of thrombomodulin, P-selectin and von Willebrand factor in 9 TTP patients during active disease and at the time of complete remission (GR). Methods. Thrombomodulin, P-selectin and von Willebrand factor were measured by enzyme immunoassay. Results. Mean thrombomodulin and von Willebrand factor plasma values were always within the normal range. P- selectin plasma levels, both in the active phase of the disease and in CR (median 312 and 185 ng/mL, respectively), were significantly higher than in normal controls (mean 96±35 ng/mL, median 88 ng/mL; p<0.05). However, the mean value of P-selectin in GR (median 185 ng/mL) was significantly lower than that observed at diagnosis (p < 0.05). In addition, an inverse relationship between P-selectin plasma levels and platelet count (r= -0.526; p= 0.03) was observed. Conclusions. These findings suggest that activation of platelets and/or endothelium may play a relevant role in the pathogenesis of TTP.