Symmetrical mutant phenotypes of the receptor EphB4 and its specific transmembrane ligand ephrin-B2 in cardiovascular development.
(25/863)
Ephrin-B2 is a transmembrane ligand that is specifically expressed on arteries but not veins and that is essential for cardiovascular development. However, ephrin-B2 is also expressed in nonvascular tissues and interacts with multiple EphB class receptors expressed in both endothelial and nonendothelial cell types. Thus, the identity of the relevant receptor for ephrin-B2 and the site(s) where these molecules interact to control angiogenesis were not clear. Here we show that EphB4, a specific receptor for ephrin-B2, is exclusively expressed by vascular endothelial cells in embryos and is preferentially expressed on veins. A targeted mutation in EphB4 essentially phenocopies the mutation in ephrin-B2. These data indicate that ephrin-B2-EphB4 interactions are intrinsically required in vascular endothelial cells and are consistent with the idea that they mediate bidirectional signaling essential for angiogenesis. (+info)
L-selectin ligands expressed by human leukocytes are HECA-452 antibody-defined carbohydrate epitopes preferentially displayed by P-selectin glycoprotein ligand-1.
(26/863)
Leukocytes express L-selectin ligands critical for leukocyte-leukocyte interactions at sites of inflammation. The predominant leukocyte L-selectin ligand is P-selectin glycoprotein ligand-1 (PSGL-1), which displays appropriate sialyl Lewis x (sLex)-like carbohydrate determinants for L-selectin recognition. Among the sLex-like determinants expressed by human leukocytes is a unique carbohydrate epitope defined by the HECA-452 mAb. The HECA-452 Ag is a critical component of L-selectin ligands expressed by vascular endothelial cells. However, HECA-452 Ag expression on human leukocyte L-selectin ligands has not been assessed. In this study, the HECA-452 mAb blocked 88-99% of neutrophil rolling on, or attachment to, adherent cells expressing L-selectin in multiple experimental systems. A function-blocking anti-PSGL-1 mAb also inhibited L-selectin binding to neutrophils by 89-98%. In addition, the HECA-452 and anti-PSGL-1 mAbs blocked the majority of P-selectin binding to neutrophils. Western blot analysis revealed that PSGL-1 immunoprecipitated from neutrophils displayed HECA-452 mAb-reactive determinants and that PSGL-1 was the predominant scaffold for HECA-452 Ag display. Leukocyte L-selectin ligands also contained sulfated determinants since culturing ligand-bearing cells with NaClO3 abrogated L-selectin binding. Consistent with this, human neutrophils expressed mRNA encoding five different sulfotransferases associated with the generation of selectin ligands: CHST1, CHST2, CHST3, TPST1, and HEC-GlcNAc6ST. Therefore, the HECA-452-defined carbohydrate determinant displayed on PSGL-1 represented the predominant L-selectin and P-selectin ligand expressed by neutrophils. (+info)
Development of erythroid and myeloid progenitors in the yolk sac and embryo proper of the mouse.
(27/863)
In this study, we have mapped the onset of hematopoietic development in the mouse embryo using colony-forming progenitor assays and PCR-based gene expression analysis. With this approach, we demonstrate that commitment of embryonic cells to hematopoietic fates begins in proximal regions of the egg cylinder at the mid-primitive streak stage (E7.0) with the simultaneous appearance of primitive erythroid and macrophage progenitors. Development of these progenitors was associated with the expression of SCL/tal-1 and GATA-1, genes known to be involved in the development and maturation of the hematopoietic system. Kinetic analysis revealed the transient nature of the primitive erythroid lineage, as progenitors increased in number in the developing yolk sac until early somite-pair stages of development (E8.25) and then declined sharply to undetectable levels by 20 somite pairs (E9.0). Primitive erythroid progenitors were not detected in any other tissue at any stage of embryonic development. The early wave of primitive erythropoiesis was followed by the appearance of definitive erythroid progenitors (BFU-E) that were first detectable at 1-7 somite pairs (E8.25) exclusively within the yolk sac. The appearance of BFU-E was followed by the development of later stage definitive erythroid (CFU-E), mast cell and bipotential granulocyte/macrophage progenitors in the yolk sac. C-myb, a gene essential for definitive hematopoiesis, was expressed at low levels in the yolk sac just prior to and during the early development of these definitive erythroid progenitors. All hematopoietic activity was localized to the yolk sac until circulation was established (E8.5) at which time progenitors from all lineages were detected in the bloodstream and subsequently in the fetal liver following its development. This pattern of development suggests that definitive hematopoietic progenitors arise in the yolk sac, migrate through the bloodstream and seed the fetal liver to rapidly initiate the first phase of intraembryonic hematopoiesis. Together, these findings demonstrate that commitment to hematopoietic fates begins in early gastrulation, that the yolk sac is the only site of primitive erythropoiesis and that the yolk sac serves as the first source of definitive hematopoietic progenitors during embryonic development. (+info)
Circulating CD2+ monocytes are dendritic cells.
(28/863)
Low levels of CD2 have been described on subsets of monocytes, macrophages, and dendritic cells. CD2 is expressed on about one-third of circulating monocytes, at levels one-half log lower than on T or NK cells, representing 2-4% of PBMC. FACS analysis of CD2+ and CD2- monocytes revealed no significant difference in the expression of adhesion molecules (CD11a/b/c), class II Ags (HLA-DR, -DQ, -DP), myeloid Ags (CD13, CD14, CD33), or costimulatory molecules (CD80, CD86). Freshly isolated CD2+ and CD2- monocytes were morphologically indistinguishable by phase contrast microscopy. However, scanning electron microscopy revealed large prominent ruffles on CD2+ monocytes in contrast to small knob-like projections on CD2- monocytes. After 2 days of culture, the CD2+ monocytes largely lost CD14 expression and developed distinct dendrites, whereas the CD2- monocytes retained surface CD14 and remained round or oval. Freshly isolated CD2+ monocytes were more potent inducers of the allogeneic MLR and more efficiently induced proliferation of naive T cells in the presence of HIV-1 gp120 than did CD2- monocytes. After culture in the presence of GM/CSF and IL-4, CD2+ monocytes were up to 40-fold more potent than monocyte-derived dendritic cells or CD2- monocytes at inducing allogeneic T cell proliferation. These findings suggest that circulating CD2+ and CD2- monocytes are dendritic cells and the precursors of macrophages, respectively. Thus, dendritic cells are far more abundant in the blood than previously thought, and they and precursors of macrophages exist in the circulation as phenotypically, morphologically, and functionally distinct monocyte populations. (+info)
Hemodynamic and metabolic responses to moderate asphyxia in brain and skeletal muscle of late-gestation fetal sheep.
(29/863)
The purpose of this study was to investigate metabolic and hemodynamic responses in two fetal tissues, hindlimb muscle and brain, to an episode of acute moderate asphyxia. Near-infrared spectroscopy was used to measure changes in total hemoglobin concentration ([tHb]) and the redox state of cytochrome oxidase (COX) simultaneously in the brain and hindlimb of near-term unanesthetized fetal sheep in utero. Oxygen delivery (DO(2)) to, and consumption (VO(2)) by, each tissue was derived from the arteriovenous difference in oxygen content and blood flow, measured by implanted flow probes. One hour of moderate asphyxia (n = 11), caused by occlusion of the maternal common internal iliac artery, led to a significant fall in DO(2) to both tissues and to a significant drop in VO(2) by the head. This was associated with an initial fall in redox state COX in the leg but an increase in the brain. [tHb], and therefore blood volume, fell in the leg and increased in the brain. These data suggest the presence of a fetal metabolic response to hypoxia, which, in the brain, occurs rapidly and could be neuroprotective. (+info)
The 400 microsphere per piece "rule" does not apply to all blood flow studies.
(30/863)
Microsphere experiments are useful in measuring regional organ perfusion as well as heterogeneity of blood flow within organs and correlation of perfusion between organ pieces at different time points. A 400 microspheres/piece "rule" is often used in planning experiments or to determine whether experiments are valid. This rule is based on the statement that 400 microspheres must lodge in a region for 95% confidence that the observed flow in the region is within 10% of the true flow. The 400 microspheres precision rule, however, only applies to measurements of perfusion to a single region or organ piece. Examples, simulations, and an animal experiment were carried out to show that good precision for measurements of heterogeneity and correlation can be obtained from many experiments with <400 microspheres/piece. Furthermore, methods were developed and tested for correcting the observed heterogeneity and correlation to remove the Poisson "noise" due to discrete microsphere measurements. The animal experiment shows adjusted values of heterogeneity and correlation that are in close agreement for measurements made with many or few microspheres/piece. Simulations demonstrate that the adjusted values are accurate for a variety of experiments with far fewer than 400 microspheres/piece. Thus the 400 microspheres rule does not apply to many experiments. A "rule of thumb" is that experiments with a total of at least 15,000 microspheres, for all pieces combined, are very likely to yield accurate estimates of heterogeneity. Experiments with a total of at least 25,000 microspheres are very likely to yield accurate estimates of correlation coefficients. (+info)
Physical training improves flow-mediated dilation in patients with the polymetabolic syndrome.
(31/863)
Endothelial dysfunction that can be detected as impaired flow-mediated dilation by ultrasonography is an early event in atherogenesis and has been demonstrated in healthy subjects with risk factors for atherosclerosis many years before the appearance of atheromatous plaques. We examined the influence of physical training on flow-mediated dilation in patients with the polymetabolic syndrome. Twenty-nine asymptomatic men aged 40 to 60 years with the polymetabolic syndrome were randomly divided between the control group and the training group, which trained 3 times a week for 12 weeks. On high-resolution ultrasound images, the diameter of the brachial artery was measured at rest, after reactive hyperemia (causing flow-mediated, endothelium-dependent dilation), and after sublingual glyceryltrinitrate (causing endothelium-independent vasodilation) in all subjects before and after the training period. The training program induced an increase of 18% in physical fitness. Flow-mediated dilation increased from 5.3+/-2.8% to 7.3+/-2.7% (P<0. 05). There was no change in body mass index, blood pressure, insulin resistance, lipids, and big endothelin-1 in either group. Flow-mediated dilation measured before training was negatively correlated with resting heart rate, waist-to-hip ratio, and insulin resistance. Resting heart rate emerged as the only independent determinant, which explained 22% of the variation in flow-mediated dilation. In conclusion, our findings suggest that a 3-month physical training program, which improved maximal exercise capacity, enhances flow-mediated dilation in patients with the polymetabolic syndrome. (+info)
Inspiratory impedance during active compression-decompression cardiopulmonary resuscitation: a randomized evaluation in patients in cardiac arrest.
(32/863)
BACKGROUND: Blood pressure is severely reduced in patients in cardiac arrest receiving standard cardiopulmonary resuscitation (CPR). Although active compression-decompression (ACD) CPR improves acute hemodynamic parameters, arterial pressures remain suboptimal with this technique. We performed ACD CPR in patients with a new inspiratory threshold valve (ITV) to determine whether lowering intrathoracic pressures during the "relaxation" phase of ACD CPR would enhance venous blood return and overall CPR efficiency. METHODS AND RESULTS: This prospective, randomized, blinded trial was performed in prehospital mobile intensive care units in Paris, France. Patients in nontraumatic cardiac arrest received ACD CPR plus the ITV or ACD CPR alone for 30 minutes during advanced cardiac life support. End tidal CO(2) (ETCO(2)), diastolic blood pressure (DAP) and coronary perfusion pressure, and time to return of spontaneous circulation (ROSC) were measured. Groups were similar with respect to age, gender, and initial rhythm. Mean maximal ETCO(2), coronary perfusion pressure, and DAP values, respectively (in mm Hg), were 13.1+/-0.9, 25.0+/-1.4, and 36.5+/-1.5 with ACD CPR alone versus 19.1+/-1.0, 43.3+/-1.6, and 56.4+/-1.7 with ACD plus valve (P<0.001 between groups). ROSC was observed in 2 of 10 patients with ACD CPR alone after 26.5+/-0.7 minutes versus 4 of 11 patients with ACD CPR plus ITV after 19.8+/-2.8 minutes (P<0.05 for time from intubation to ROSC). Conclusions-Use of an inspiratory resistance valve in patients in cardiac arrest receiving ACD CPR increases the efficiency of CPR, leading to diastolic arterial pressures of >50 mm Hg. The long-term benefits of this new CPR technology are under investigation. (+info)