Blood
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Co-localization of blood platelets and granulocytes at sites of hemostasis and inflammation has triggered an intense interest in possible interactions between these cellular processes and induction of vessel wall injury. Leukocyte adhesion to endothelial cells decreases with increasing shear and is dependent on an initial rolling phase mediated by selectins. We hypothesized that flow-dependent platelet adhesion at an injured vessel wall will lead to P-selectin expression by platelets, thus mediating leukocyte co-localization. ⋯ Studies with specific antibodies showed that the platelet-dependent neutrophil adhesion was selectin-mediated. Inhibition of P-selectin caused a marked inhibition of adhesion at high shear stress, whereas the role of leukocyte L-selectin was less pronounced. beta2-Integrin-blocking antibodies inhibited static neutrophil adhesion. fMLP induced L-selectin shedding from leukocytes, resulting in decreased leukocyte adhesion. In conclusion, platelet-dependent hemostasis at the ECM appears to be a powerful intermediate in neutrophil-vessel wall interactions at shear stresses that normally do not allow neutrophil adhesion to intact endothelium.
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Spur cell anemia may occur in severe liver disease including alcoholic cirrhosis. Spur cell anemia red blood cells (RBCs) have a characteristic morphology, with irregular projections, an increased ratio of membrane cholesterol (Ch) to phospholipid, evidence of oxidative damage, and shortened survival resulting in hemolytic anemia. Normal RBCs may acquire many of the features of spur cells either by transfusion into a spur cell patient or in an in vitro model system that loads the RBC membrane with Ch relative to phospholipid by means of Ch-rich, phospholipid-Ch sonicates. ⋯ Similar LAT assay results were obtained using [14C]palmitoyl LPC as the precursor. We conclude that Ch-loading of RBC membranes results in inhibition of LAT in the cell-free system in vitro and may account for the inhibited phospholipid repair in Ch-loaded intact RBCs in vitro and in spur cell anemia RBCs in vivo. Decreased ability to replace peroxidized membrane fatty acid by this metabolic pathway may contribute to the hemolytic process in spur cell anemia.
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Iron-regulatory proteins (IRP1 and IRP2) are RNA-binding proteins that bind to stem-loop structures known as iron-responsive elements (IREs). IREs are located in the 5'- or 3'-untranslated regions (UTRs) of specific mRNAs that encode proteins involved in iron homeostasis. The binding of IRPs to 5' IREs represses translation of the mRNA, whereas the binding of IRPs to 3' IREs stabilizes the mRNA. ⋯ The increase in IRE binding activity of IRP1 was coincident with the translational repression of ferritin synthesis. Transferrin receptor (TfR) mRNA levels were increased in cells treated with NO.-generating compounds, but not in cytokine- and LPS-treated cells. Our data indicate that IRP1 and IRP2 are differentially regulated by NO. in rat hepatoma cells, suggesting a role for IRP1 in the regulation of iron homeostasis in vivo during hepatic inflammation.
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Comparative Study
Phospholipase A2 levels in acute chest syndrome of sickle cell disease.
Acute chest syndrome (ACS) is associated with significant morbidity and is the leading cause of death in patients with sickle cell disease (SCD). Recent reports suggest that bone marrow fat embolism can be detected in many cases of severe ACS. Secretory phospholipase A2 (sPLA2) is an important inflammatory mediator and liberates free fatty acids, which are felt to be responsible for the acute lung injury of the fat embolism syndrome. ⋯ In patients with ACS sPLA2 levels were 100-fold greater than normal control values, 35 times greater than values in SCD patients at baseline, and five times greater than non-SCD patients with pneumonia. The degree of SPLA2 elevation in ACS correlated with three different measures of clinical severity and, in patients followed sequentially, the rise in SPLA2 coincided with the onset of ACS. The dramatic elevation of SPLA2 in patients with ACS but not in patients with vaso-occlusive crisis or non-SCD patients with pneumonia and the correlation between levels of SPLA2 and clinical severity suggest a role for SPLA2 in the diagnosis and, perhaps, in the pathophysiology of patients with ACS.
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Randomized Controlled Trial Clinical Trial
Effects of granulocyte colony-stimulating factor on plasma cytokine and cytokine receptor levels and on the in vivo host response to endotoxin in healthy men.
We investigated the effects of granulocyte colony-stimulating factor (G-CSF) on cytokine and cytokine receptor plasma levels and on the in vivo host response to Salmonella abortus equi endotoxin in healthy males. Twenty volunteers received 0.8 ng/kg endotoxin and saline intravenously 1 week apart in randomized order. Twelve hours before both experiments, 10 of these subjects were pretreated with 300 micrograms G-CSF subcutaneously. ⋯ Endotoxin-induced increases in IL-6, cortisol, and heart rate were not modified by G-CSF pretreatment. Endotoxin administration induced a transient 50% reduction in leukocyte counts in the G-CSF-pretreated subjects that was not seen in the control group. We conclude that a single stand dose of G-CSF increases the plasma levels of cytokines and cytokine receptors and considerably modifies the host response of healthy humans to a low dose of endotoxin.