With our adaptations it is possible to discriminate tandem conjugates of Cy5, Cy5.5, and Cy7 for eight-color immunophenotyping. Using this method, novel rare subsets of NK and NKT cells that are CD4/CD8 double positive are reported for the first time.

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Pregnancy (including puerperium) is a period of hypercoagulability and seems to be an independent major risk factor for venous thromboembolism (VTE). However, the basis of the increased risk of VTE in pregnancy and around delivery is unknown. We hypothesized that changes in PRL, which is a prominently increased hormone during pregnancy and lactation, might be involved in the activation of platelets. To investigate platelet functional abnormalities in pregnancy, we assessed the ADP-stimulated and nonstimulated P-selectin expression of platelets in 42 consecutive pregnant women, 22 normo- and hyperprolactinemic patients with pituitary tumors, and controls. In addition, the aggregation of platelets by human PRL in vitro was studied. We found a significant correlation between PRL values and ADP stimulation of platelets in pregnant women (r = 0.56; P < 0.0001) and patients with pituitary tumors (r = 0.57; P = 0.006). Hyperprolactinemic pregnant women or hyperprolactinemic patients with pituitary tumors revealed significantly higher ADP stimulation of platelets (P < 0.0001) than healthy controls or normoprolactinemic patients with pituitary tumors. These results were reconciled by increased in vitro stimulation and aggregation of platelets using human PRL. Our novel findings demonstrate that hyperprolactinemia causes increased platelet aggregation via ADP stimulation both in vitro and in vivo. Moreover, our data indicate that PRL may be a physiological cofactor of the delicate coagulation balance during pregnancy and puerperium that might explain the increased risk of VTE in pregnant women around delivery. Further studies of the interaction between PRL and platelets will clarify the clinical relevance of hyperprolactinemia as a potential risk factor for VTE.

To elucidate potential causes for differing bleeding phenotypes of haemophilic patients of identical degree of coagulation factor deficiency, we investigated 21 male patients with severe haemophilia. Median annual coagulation factor demand and the extent of haemophilic arthropathy were used to discriminate between intensely and less intensely haemorrhagic phenotypes. Haemophiliacs with a median annual coagulation factor demand of 800 IU per kg bodyweight or more and with three or more joints affected by haemophilic arthropathy represented the intensely haemorrhagic phenotype group; all other patients comprised the less intense group. The discriminator values represent the respective medians of the overall group. The results of activated partial thromboplastin time, endogenous thrombin potential, pro- and anticoagulant factor analysis did not differ between the two groups. Median tissue-type plasminogen activator concentration (TPA) was elevated significantly in haemophiliacs with an intensely haemorrhagic phenotype, as was the activity of the thrombin-activatable fibrinolysis inhibitor. Median activity of the plasminogen activator inhibitor 1 (PAI 1) and the concentration of TPA-PAI 1 complexes were increased to approximately double those in nonsevere haemophiliacs. Coexistent congenital thrombophilia was found significantly more often in the less intensely haemorrhagic group. Thus, increased stimulation of the fibrinolytic system was associated with a more intensely haemorrhagic phenotype in our patients. We hypothesize that ineffective haemophilic haemostasis in response to trauma evokes a protracted stimulation of the entire haemostatic system, including costimulation of fibrinolysis. The absence of coexistent congenital thrombophilia predisposes to excess stimulation of fibrinolysis, which cannot be downregulated effectively due to the dysfunctional intrinsic pathway. The association of a more intensely haemorrhagic phenotype with a paradoxical hyperstimulation of the fibrinolytic system resembles a vicious circle, where bleeding seems to cause predisposition to more bleeding.

Platelet volume has been reported to be increased in vascular disease. Therefore, we studied the relationship of mean platelet volume and platelet count as well as flow cytometrically measured platelet size and platelet function in 50 patients with peripheral arterial disease and 50 healthy volunteers. Platelet activation was measured by P-selectin expression analysis on resting and on stimulated platelets, and the determination of platelet aggregates and platelet-derived microparticles using flow cytometry. P-Selectin expression on platelets was significantly elevated in patients suffering from peripheral arterial disease (all P<0.0001). Platelet aggregates (P<0.0001) and platelet-derived microparticles (P<0.0001) were significantly higher in the patient group compared with controls, whereas mean platelet volume and platelet count showed no significant differences. Platelet count was inversely related to mean platelet volume in patients and controls (r = -0.43, P<0.001). The present study supports the hypothesis of platelet hyperreactivity and circulating activated platelets in peripheral arterial disease. Mean platelet volume, and platelet count cannot be used as predictive markers for platelet activation in peripheral arterial disease patients.