BackgroundSickle cell disease is characterized by a hypercoagulable state as a result of multiple factors, including chronic hemolysis and circulating cell-derived microparticles. There is still no consensus on the cellular origin of such microparticles and the exact mechanism by which they may enhance coagulation activation in sickle cell disease. Design and MethodsIn the present study, we analyzed the origin of circulating microparticles and their procoagulant phenotype during painful crises and steady state in 25 consecutive patients with sickle cell disease. ResultsThe majority of microparticles originated from platelets (GPIIIa,CD61) and erythrocytes (glycophorin A,CD235), and their numbers did not differ significantly between crisis and steady state. Erythrocyte-derived microparticles strongly correlated with plasma levels of markers of hemolysis, i.e. hemoglobin (r=-0.58, p<0.001) and lactate dehydrogenase (r=0.59, p<0.001), von Willebrand factor as a marker of platelet/endothelial activation (r=0.44, p<0.001), and D-dimer and prothrombin fragment F1+2 (r=0.52, p<0.001 and r=0.59, p<0.001, respectively) as markers of fibrinolysis and coagulation activation. Thrombin generation depended on the total number of microparticles (r=0.63, p<0.001). Anti-human factor XI inhibited thrombin generation by about 50% (p<0.001), whereas anti-human factor VII was ineffective (p>0.05). The extent of factor XI inhibition was associated with erythrocyte-derived microparticles (r=0.50, p=0.023). ConclusionsWe conclude that the procoagulant state in sickle cell disease is partially explained by the factor XI-dependent procoagulant properties of circulating erythrocyte-derived microparticles.Key words: microparticles, sickle cell disease, coagulation activation, hemolysis. Citation

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On vascular damage, coagulation is initiated by extravascular tissue factor (TF). Intravascular TF, which is present on circulating cell-derived vesicles, is noncoagulant under physiologic conditions but prothrombotic under pathologic conditions. Human saliva triggers coagulation, but the mechanism and physiologic relevance are unknown. Because saliva is known to contain TF, we hypothesized that this TF may also be associated with cell-derived vesicles to facilitate coagulation when saliva directly contacts blood.The saliva-induced shortening of the clotting time of autologous plasma and whole blood from healthy subjects (n ‫؍‬ 10) proved TF-dependent. This TF was associated with various types of cell-derived vesicles, including microparticles and exosomes. The physiologic function was shown by adding saliva to human pericardial wound blood collected from patients undergoing cardiac surgery. Addition of saliva shortened the clotting time from 300 ؎ 96 to 186 ؎ 24 seconds (P ‫؍‬ .03). Our results show that saliva triggers coagulation, thereby reducing blood loss and the risk of pathogens entering the blood. We postulate that our reflex to lick a wound may be a mechanism to enable TF-exposing vesicles, present in saliva, to aid in the coagulation process and thus protect the organism from entering pathogens. This unique compartmentalization may be highly conserved because also animals lick their wounds. (Blood. 2011;117(11):3172-3180)

Abstract-An elevated level of C-reactive protein is a strong predictor of cardiovascular events in elderly persons. Whether C-reactive protein has direct adverse vascular effects or is a marker of aspecific systemic inflammation remains to be determined. The aim of this study was to investigate the relation between C-reactive protein and the occurrence of fatal strokes in elderly persons. In the Leiden 85-Plus Study, a population-based prospective follow-up study, we studied the levels of C-reactive protein in 80 participants who died from stroke within the first 5 years of follow-up. Levels of C-reactive protein were determined in serum samples at baseline. Levels of C-reactive protein were also determined in 82 control subjects who survived for the first 5 years of follow-up and in 83 participants who died from noncardiovascular causes. Mortality risks were estimated with logistic regression and adjusted for differences in age, sex, smoking, medication, total cholesterol, history of diabetes or hypertension, and previous cardiovascular events. Levels of C-reactive protein at baseline were 2-fold higher in subjects who died from stroke than in control subjects (median 5.7 versus 2.7 mg/L, PϽ0.005). The levels of C-reactive protein in subjects who died from stroke or from noncardiovascular causes were similar (median 5.7 versus 4.9 mg/L, Pϭ0.7). The risk of death from stroke as well as from noncardiovascular causes increased linearly up to 10-fold in subjects with the highest levels of C-reactive protein at baseline (PϽ0.001). The levels of C-reactive protein were lower when more time had elapsed between blood sampling and time of death during follow-up (P‫.)10.0؍‬ C-reactive protein is a strong but nonspecific risk factor of fatal stroke in old persons. The data do not support the idea that C-reactive protein has direct vascular effects that underlie fatal cerebrovascular disease.