Fas/CD95/APO-1 can function as a death receptor for neuronal cells in vitro and in vivo and is upregulated following cerebral hypoxic-ischemic injury to the developing rat brain

Fas/CD95/Apo-1 is a cell surface receptor that transduces apoptotic death signals following activation and has been implicated in triggering apoptosis in infected or damaged cells in disease states. Apoptosis is a major mechanism of neuronal loss following hypoxic-ischemic injury to the developing brain, although the role of Fas in this process has not been studied in detail. In the present study, we have investigated the expression and function of Fas in neuronal cells in vitro and in vivo. Fas was found to be expressed in the 14 day old rat brain, with strongest expression in the cortex, hippocampus and cerebellum. Cross-linking of Fas induced neuronal apoptosis both in neuronal PC12 cells in culture and following intracerebral injection in vivo, indicating that neuronal Fas was functional as a death receptor. This death was shown to be caspase dependent in primary neuronal cultures and was blocked by the selective caspase 8 inhibitor IETD. Finally, cerebral hypoxia-ischemia resulted in a strong lateralised upregulation of Fas in the hippocampus, that peaked six to twelve hours after the insult and was greater on the side of injury. These results suggest that Fas may be involved in neuronal apoptosis following hypoxic-ischemic injury to the developing brain.

CD45 engagement induces L-selectin down-regulation

The CD45 glycoprotein isoforms exhibit a receptor-like composition and display intracellular protein tyrosine phosphatase (PTPase) activity. The present study links CD45 to the regulation of L-selectin (CD62L), a leucocyte glycoprotein important for extravasation and homotypic aggregation. Monoclonal antibodies (MoAbs) IOL1b and AICD45.2, but not GAP8.3, all of which are directed against common CD45 epitopes, were found to elicit lymphocyte L-selectin down-regulation. Lymphocyte L-selectin down-regulation in response to anti-CD45 MoAbs was enhanced by high cell density and partially antagonized by the protein tyrosine kinase (PTK) inhibitor, herbimycin A. The MoAbs IOL1b, AICD45.2 and GAP8.3 recognized granulocyte-expressed CD45 but did not induce loss of L-selectin expression of granulocytes. In contrast, the CD45 PTPase inhibitor, vanadate, induced L-selectin down-regulation both in lymphocytes and granulocytes. The PTPase activation by nitric oxide (NO) or the NO-generating compound, sodium nitroprusside, did not affect L-selectin surface expression. Increased concentrations of soluble L-selectin were detected after anti-CD45 or vanadate-induced down-regulation of L-selectin surface expression. While activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate (PMA) induces rapid L-selectin down-regulation of L-selectin surface expression in both lymphocytes and granulocytes, the PKC inhibitor, H 7, was also found to down-regulate lymphocyte and granulocyte L-selectin surface expression. The inhibitor H 7 synergized with vanadate in down-regulating lymphocyte L-selectin surface expression, but partially inhibited vanadate-induced granulocyte L-selectin down-regulation. The results suggest that in a cell type-specific fashion the PKC system and tyrosine phosphorylation and dephosphorylation cascades are involved in the regulation of L-selectin surface expression.

Cerebrospinal fluid soluble L-selectin (sCD62L) in meningoencephalitis

The leucocyte adhesion molecule L-selectin (CD62L) is rapidly cleaved off proteolytically after cell activation, generating soluble L-selectin (sCD62L) molecules. sCD62L concentrations were determined in 185 cerebrospinal fluid (CSF) samples obtained from children aged 1 month to 17 years. In 36 CSF samples of children with meningoencephalitis, sCD62L was significantly higher (median 209 fmol/ml) than in samples of children with other febrile diseases (n = 67, median 50 fmol/ml) or non-febrile disorders (n = 82, median 44 fmol/ml). There was a positive correlation between CSF protein and CSF sCD62L (rS = 0.68), suggesting that a disturbed blood-brain barrier contributes to raised sCD62L concentrations in the CSF. However, the CSF sCD62L/protein ratio of children with meningoencephalitis was significantly higher than in children with other febrile diseases or non-febrile disorders, indicating that sCD62L concentrations in children with meningoencephalitis were higher than expected from plasma leakage alone. It is concluded that both an impaired blood-brain barrier and the generation of sCD62L by infiltrating leucocytes contribute to raised CSF sCD62L concentrations in children with meningoencephalitis.

Soluble L-selectin (sCD62L) umbilical cord plasma levels increase with gestational age

L-Selectin (CD62L) is a leukocyte surface membrane glycoprotein involved in extravasation and homotypic aggregation which is rapidly cleaved off after cellular activation. From culture supernatants and body fluids, soluble L-selectin (sCD62L) has been recovered with its functional activity retained. We devised a sensitive enzyme-linked immunoassay for quantitation of sCD62L which was used to measure sCD62L in umbilical cord plasma of 255 human newborns with a gestational age (GA) of 23-43 wk (median 38 wk). sCD62L levels ranged from 1.14-13.8 pmol/mL (median 7.2 pmol/mL) and showed strong correlations with GA (r = 0.71, p < 0.001), birth weight (r = 0.66, p < 0.001), and absolute neutrophil cell counts (ANC) (r = 0.62, p < 0.001) obtained from a peripheral vein within the first 6 h of life (n = 153), whereas there was a weak inverse correlation with absolute normoblast counts (r = -0.27, p < 0.001). In multiple regression analysis, only GA and ANC retained a significant association with sCD62L levels (p < 0.001). Decreased sCD62L levels were found to be associated with multiple gestation (4.8 +/- 2.4 pmol/mL versus 7.7 +/- 2.3 pmol/mL, p < 0.05) also when considering GA and ANC as covariates. In contrast, increased sCD62L levels in infants born from meconium-stained amniotic fluid, and decreased levels in newborns with acute bacterial infection could be fully attributed to differences in GA and ANC.(ABSTRACT TRUNCATED AT 250 WORDS)

L-selectin is down-regulated in umbilical cord blood granulocytes and monocytes of newborn infants with acute bacterial infection

The leukocyte glycoprotein L-selectin mediates an early step in the recruitment of leukocytes to sites of inflammation. L-Selectin surface expression is rapidly down-regulated by inflammatory signals in vitro. In a prospective study, we found L-selectin expression on umbilical cord blood granulocytes and monocytes to be significantly decreased in newborn infants with acute bacterial infection compared with controls (p < 0.01). A significantly reduced L-selectin expression of both granulocytes and monocytes was also found to be associated with an increased neutrophil immature/total ratio (p < 0.01) but not with other laboratory markers of neonatal sepsis. There was no apparent impact of prematurity, low birth weight, gestational hypertension, or gestational diabetes on L-selectin expression. Although the mode of delivery did not affect granulocyte L-selectin expression, umbilical cord blood monocytes showed an increased L-selectin expression after emergency cesarean delivery compared with samples obtained after elective cesarean or vaginal delivery (p < 0.01). We conclude that acute systemic inflammation results in down-regulation of granulocyte and monocyte L-selectin expression in vivo similar to that observed in vitro.

Down-regulation of L-selectin surface expression by various leukocyte isolation procedures

L-selectin, a cell surface glycoprotein expressed on lymphocytes, granulocytes, and monocytes, has been implicated in lymphocyte homing and extravasation of phagocytic leukocytes into areas of inflammation. Considerable differences of L-selectin expression among various individuals has been reported, with clinical correlations to perinatal events, maturation, and circadian rhythm. In this study, L-selectin expression of various white blood cells was found to be differentially sensitive to ficoll-hypaque or percoll density gradient centrifugation. After density gradient centrifugation, a significant loss of median monocyte L-selectin expression was observed when compared to time and temperature-matched controls or results obtained by whole blood incubation with anti-L-selectin monoclonal antibodies followed by simultaneous leukocyte fixation and red cell lysis. Mock treatment itself was associated with a variable L-selectin loss of monocytes but not lymphocytes or granulocytes. Ficoll-hypaque or percoll density gradient centrifugation resulted in significant L-selectin down-regulation of lymphocytes while granulocytes separated from lymphocytes and monocytes by ficoll-hypaque or percoll retained full L-selectin surface reactivity. L-selectin downregulation was seen also after colloid sedimentation with hydroxy-ethyl starch. It is concluded that unseparated blood should be used for measuring L-selectin expression.

Down-regulation of L-selectin surface expression by various leukocyte isolation procedures

L-selectin, a cell surface glycoprotein expressed on lymphocytes, granulocytes, and monocytes, has been implicated in lymphocyte homing and extravasation of phagocytic leukocytes into areas of inflammation. Considerable differences of L-selectin expression among various individuals has been reported, with clinical correlations to perinatal events, maturation, and circadian rhythm. In this study, L-selectin expression of various white blood cells was found to be differentially sensitive to ficoll-hypaque or percoll density gradient centrifugation. After density gradient centrifugation, a significant loss of median monocyte L-selectin expression was observed when compared to time and temperature-matched controls or results obtained by whole blood incubation with anti-L-selectin monoclonal antibodies followed by simultaneous leukocyte fixation and red cell lysis. Mock treatment itself was associated with a variable L-selectin loss of monocytes but not lymphocytes or granulocytes. Ficoll-hypaque or percoll density gradient centrifugation resulted in significant L-selectin down-regulation of lymphocytes while granulocytes separated from lymphocytes and monocytes by ficoll-hypaque or percoll retained full L-selectin surface reactivity. L-selectin downregulation was seen also after colloid sedimentation with hydroxy-ethyl starch. It is concluded that unseparated blood should be used for measuring L-selectin expression.

Topo-optical investigations of human erythrocyte glycocalyx conformational changes induced by dextran

Cell surface properties are involved in the aggregation process of red blood cells. Using the topo-optical toluidine blue reaction, conformational changes of the glycocalyx (main component glycophorin A) were found when red blood cells were incubated and fixed in the presence of dextran. Relative differences in optical path as a measure of red blood cell membrane anisotropy decreased in relation to dextran concentration during fixation. These conformational changes could not be detected by electrophoretic measurements. When incubating, fixing and staining red blood cells in the presence of dextran, anisotropy decreased only at low dextran concentrations and increased at rising dextran concentrations. This biphasic course of differences in optical path seems to be due to different effects of dextran superimposing upon each other: a disturbing influence on the spatial order of sialic acid carrying oligosaccharide side chains due to H-bond interaction, and an increase in the size of dye aggregates and suppression of the thermal motion of macromolecules at higher dextran concentrations.

The rate of lateral diffusion of phospholipids in erythrocyte microvesicles

31P-NMR spectra of phospholipids in membranes of erythrocyte microvesicles isolated from outdated blood units were recorded in the temperature range 5 to 55 degrees C. Within that range the lineshape is strongly influenced by an increasing rate of lateral diffusion of phospholipids. At 36 degrees C a diffusion constant, D, of (2 +/- 1) X 10(-12) m2/s was obtained. The diffusion rate is by a factor of 3 to 10 greater than in erythrocyte membranes measured by the photobleaching technique and is comparable with values obtained for several lipid model membranes. The differences in lateral diffusion rates are probably connected with the depletion of microvesicle membranes in membrane proteins.

Activation of acetylcholine esterase (ACHE) as a sign for erythrocyte membrane alteration

In vitro activity determination of membrane bound acetylcholine esterase (ACHE) of intact erythrocytes and differently altered RBC forms by means of the ELLMAN method yielded increase in activity in erythrocyte/vesicle mixtures and ghosts. Alteration of the cells by treatment with periodate, neuraminidase and trypsin leads to no, weak or clear decrease in the activity of this enzyme. Old cells also show a clear decrease in activity. When cells were treated with diamide ACHE is at first functionally inhibited, finally, however, it reaches supernormal values of activity. Possible causes for the different behaviour of ACHE in dependence on the degree of alteration of the erythrocytes are discussed. The results of the measurements were compared with the ultrahistochemical ACHE reactions according to KARNOVSKY (thiocholine--copper ferricyanide method) and IWAYAMA (lead thiocholine method). The influence of several components of the KARNOVSKY'S histochemical reaction mixture on ACHE activity was tested. The investigations suggest that disintegration of the erythrocyte membrane is accompanied with activation of the ACHE molecules which are nearly inactive in the intact membrane. This activation contributes to the positive histochemical ACHE test, which is an indicator reaction of membrane disintegration. Nearly intact membranes show a negative reaction. On the basis of these results we could show that physiological enucleation of normoblasts is connected with the formation of disintegrated membrane areas and their discharge from the future reticulocyte membrane.

Topo-optical investigations of the human erythrocyte glycocalyx-age related changes

The conformational state of the glycocalyx of the intact and altered erythrocyte membrane was studied by means of the topo-optical toluidine blue reaction, i.e. induced membrane birefringence. High membrane anisotropy represents the normal glycocalyx structure and its decline represents their perturbation. The results show that the glycocalyx structure is changed during ageing of the erythrocytes in vivo as well as in vitro. During fluid preservation, in vitro ageing and vesiculation of cells in vitro, a subpopulation of cells showed a decline of membrane anisotropy, but other cells demonstrated abnormally high values. In the latter cases, there is usually a correlation to spherocytes. From this point of view, it is to be assumed that spherogenesis during cell ageing is induced by cell vesiculation. This leads to a remodelling of an intact plasmalemma. In contrast, the cell fractions which are probably non-vesiculating seem to be more or less damaged by membrane and/or plasmic hydrolases. This can be mimicked by neuraminidase and protease treatment of erythrocytes in vitro. Membrane lesions caused by freeze preservation of red blood cells are rare. The topo-optical results are interpreted according to the assumptions of the theory of membrane anisotropy, i.e. the formation of dye-stuff micelles at distinct, clustered, sialylated carbohydrate chains of the glycophorin A.

Acceleration of coagulation by spectrin-free erythrocytic vesicles. Evidence for lipid flip-flop during vesicle formation

Spectrin-free erythrocytic vesicles isolated from outdated liquid-preserved blood samples show a distinct increase of the clot-promoting activity compared with membrane phospholipid equivalents of intact erythrocytes. We suppose that, among other remodelling processes, local spectrin detachment from the inner membrane surface may trigger a flip-flop-mediated disturbance of the membrane lipid asymmetry. The interactions of spectrin with the cytoplasmic membrane surface seem to be essential for the structural membrane integrity including the lipid asymmetry.

Metabolic depletion of erythrocytes is accompanied by a decrease of sialic acid during blood bank storage: a reply

Erythrocytes lose about 10% of their sialic acid during banking in ACD-AG medium. In contrast to these findings, Pessina et al. could not detect a significant banking-related sialic acid decrease. The present paper explains this discrepancy. The vesiculation of erythrocytes is mainly responsible for the observed sialic acid loss during blood preservation.

Remarks on the spatial structure of the external segment of glycophorin A

A model of the possible structure of the N-terminal part of glycophorin A is suggested. According to this model, in isotonic salt solutions of physiologic pH the peptide chain of the extracellular segment of glycophorin A is arranged parallel to the membrane with its carbohydrate side chains orientated perpendicularly to the lipid bilayer. Decreases of the pH or of the ionic strength result in a structural remodeling of this segment, there is at the very least a partial detachment of the glycosylated peptide backbone from the membrane's lipid layer.

[Vesiculation of erythrocytes. 1. Isolation of a vesicle fraction from banked blood]

The study is concerned with the isolation of erythrocyte vesicles. The procedure suggested employs graded centrifugation of basal portions of the spontaneous cell sedimentation of banked blood. Shape of vesicles and the purity of fractions obtained were examined electron microscopically.

Alteration of the enucleating erythroblast glycocalyx

Plasmalemmal differentiation of the enucleating normoblast of rabbit and rat was studied by means of cytochemical methods and freeze-etching. Staining with colloidal iron revealed about identical amounts of iron particles bound to various areas of the normoblast membrane. Cationized ferritin and ruthenium red, likewise, failed in the demonstration of significant changes of the enucleating normoblast glycocalyx. Despite these findings the topo-optical staining with toluidine blue showed the plasmalemmal envelope of the protruding normoblast nucleus moderately birefringent, clearly discriminated from the intense anisotropic staining of the future reticulocyte membrane. The ferritin-labeled snail lectin anti AHP localized a great number of binding sites at the plasmalemmal envelope of the nucleus under extrusion. That is in sharp contrast with rather low lectin binding to the future reticulocyte membrane which amounts to about 30 to 50% of the nuclear envelope label. The findings provide evidence of unmasking of bindings sites of the normoblast membrane. Apparently, the effect is due to conformational changes of the cell membrane, rather than it could be attributed to degradation of glycoproteins. Moreover, enucleation kinetics may also be related to supramolecular changes of membrane structure albeit missing evidence for the rearrangement of membrane particles.

Phosphorylated spectrins are likely constituents of major Ca2+ affinity sites

Fixation with Ca2+ -glutaraldehyde of ghosts results in opaque membrane associated deposits similar to Ca2+ binding sites of native human erythrocytes. Following brief incubation in an ATP medium the number and size of major Ca2+ affinity sites is considerably enhanced. In addition to major Ca2+ affinity sites multiple minor sites are lining either aspect of the ghost membrane. Ghosts fixed with EDTA-glutaraldehyde are devoid of major Ca2+ affinity sites and they exhibit extreme low overall opacity. Ghosts previously partially despectrinated by incubation in 0.5 mM EDTA have lost major Ca2+ affinity sites, although minor binding sites appear unimpaired. The findings provide evidence of the demonstration of phosphorylated spectrins in major Ca2+ affinity sites.

Reversible conformational changes of plasmalemmal glycoproteins

Repeated incubations of human red blood cells in low ionic isotonic sucrose result in an instantaneous agglutination. In the same medium which had caused the agglutination, erythrocytes completely disagglutinate within 60 to 90 min. Disagglutination is accompanied by the efflux of cellular ions, which causes a 500-fold increase of extracellular K+. Decomposition of agglutinates occurs at once upon addition to the medium of about 3 mM KCL. It will be inhibited for hours, if the medium is renewed twice an hour. Erythrocytes washed successively with phosphate buffered saline and isotonic sucrose are devoid of adhering blood plasma proteins. If these cells were fixed with glutaraldehyde in isotonic sucrose they had lost a) their anisotropic staining with toluidine blue, and b) most of their colloidal iron binding capacity. The staining with ruthenium red and the electrophoretic velocity of these erythrocytes apparently were identical with the controls. The findings are considered evidence of the reversible unfolding of glycocalyx glycoproteins in the low ionic medium.

Adsorbed proteins mask negatively charged sites of the erythrocyte glycocalyx

Protein masking of charged sites of the erythrocyte glycocalyx was studied by means of the colloidal iron affinity. Washed red cells were fixed with glutaraldehyde such as to stabilize their glycocalyx and to inhibit conformational changes during posttreatment. Following the incubation in an ionic protein solution, proteins adsorbed to the cell surface were insolubilized by repeated treatment with low ionic isotonic surcose. Erythrocytes coated with precipitated proteins exhibited a rough surface. Their iron binding capacity was reduced considerably. In comparison with serum albumin, masking by gamma globulin was more efficient, apparently, because of its insolubility in low ionic media. High ionic incubation of coated erythrocytes resolubilized adsorbed proteins and unmasked negatively charged groups of the glycocalyx.