Red blood cell surface adhesion molecules: their possible roles in normal human physiology and disease

Scanning Electron and Atomic Force Microscopic Analysis of Erythrocytes in a Cohort of Atopic Asthma Patients—A Pilot Study

Background: Non-communicable diseases are often associated with chronic inflammation, placing patients suffering from these conditions at a higher risk of thrombosis and other complications. The pathophysiology of asthma and/or atopic asthma is also linked to chronic inflammation, which consequently may alter blood parameters including erythrocyte structure and function. Methodology: The objective of this study was to evaluate differences in erythrocytes between patients with atopic asthma (n = 30) and healthy individuals (n = 30) by evaluating routine haematological parameters; structures and axial ratios of erythrocytes using light microscopy; erythrocyte membrane elasticity using atomic force microscopy; and erythrocyte ultrastructure using scanning electron microscopy. Results: The haematological findings of healthy participants and patients suffering from asthma were within normal clinical ranges together with significantly higher levels of circulating monocytes (p = 0.0066), erythrocytes (p = 0.0004), haemoglobin (p = 0.0057), and haematocrit (p = 0.0049) in asthma patients. The analysis of eosin-stained erythrocytes by light microscopy showed more echinocytes, acanthocytes, and ovalocytes compared to controls and a significant difference in axial ratios (p < 0.0001). Atomic force microscopy findings showed reduced erythrocyte membrane elasticity in asthmatic erythrocytes (p = 0.001). Ultrastructural differences in erythrocytes were visible in the asthma group compared to controls. Conclusion: Altered erythrocyte ultrastructural morphology and a significant change in the haematological profile are evident in atopic asthma and may influence common complications associated with asthma. The impact of these changes on the physiological mechanisms of coagulation and the pathophysiology of asthma needs to be further elucidated.

The impact of biological age of red blood cell on in vitro endothelial activation markers

Introduction: Blood donor characteristics influence red blood cell transfusion outcomes. As donor sex affects the distribution of young to old RBCs in the circulation, we hypothesized that the amount of circulating young RBCs in the blood product are associated with immune suppression.

Materials and Methods: Blood samples were collected from healthy volunteers and density fractionated into young and old subpopulations. In an activated endothelial cell model, RBC adhesion to endothelium and secretion of endothelial activation markers were assessed. The impact of RBC biological age was also assessed in a T cell proliferation assay and in a whole blood stimulation assay.

Results: After Percoll fractionation, young RBCs contained more reticulocytes compared to old RBCs. Young RBCs associated with lower levels of E-selectin, ICAM-1, and vWF from activated endothelial cells compared to old RBCs. RBC subpopulations did not affect T cell proliferation or cytokine responses following whole blood stimulation.

Conclusion: Young RBCs contain more reticulocytes which are associated with lower levels of endothelial activation markers compared to old RBCs.

Antithrombin-III mitigates thrombin-mediated endothelial cell contraction and sickle red blood cell adhesion in microscale flow

Individuals with sickle cell disease (SCD) have persistently elevated thrombin generation that results in a state of systemic hypercoagulability. Antithrombin‐III (ATIII), an endogenous serine protease inhibitor, inhibits several enzymes in the coagulation cascade, including thrombin. Here, we utilize a biomimetic microfluidic device to model the morphology and adhesive properties of endothelial cells (ECs) activated by thrombin and examine the efficacy of ATIII in mitigating the adhesion of SCD patient‐derived red blood cells (RBCs) and EC retraction. Microfluidic devices were fabricated, seeded with ECs, and incubated under physiological shear stress. Cells were then activated with thrombin with or without an ATIII pretreatment. Blood samples from subjects with normal haemoglobin (HbAA) and subjects with homozygous SCD (HbSS) were used to examine RBC adhesion to ECs. Endothelial cell surface adhesion molecule expression and confluency in response to thrombin and ATIII treatments were also evaluated. We found that ATIII pretreatment of ECs reduced HbSS RBC adhesion to thrombin‐activated endothelium. Furthermore, ATIII mitigated cellular contraction and reduced surface expression of von Willebrand factor and vascular cell adhesion molecule‐1 (VCAM‐1) mediated by thrombin. Our findings suggest that, by attenuating thrombin‐mediated EC damage and RBC adhesion to endothelium, ATIII may alleviate the thromboinflammatory manifestations of SCD.

In Silico Analysis of the Multi-Targeted Mode of Action of Ivermectin and Related Compounds

Some clinical studies have indicated activity of ivermectin, a macrocyclic lactone, against COVID-19, but a biological mechanism initially proposed for this anti-viral effect is not applicable at physiological concentrations. This in silico investigation explores potential modes of action of ivermectin and 14 related compounds, by which the infectivity and morbidity of the SARS-CoV-2 virus may be limited. Binding affinity computations were performed for these agents on several docking sites each for models of (1) the spike glycoprotein of the virus, (2) the CD147 receptor, which has been identified as a secondary attachment point for the virus, and (3) the alpha-7 nicotinic acetylcholine receptor (α7nAChr), an indicated point of viral penetration of neuronal tissue as well as an activation site for the cholinergic anti-inflammatory pathway controlled by the vagus nerve. Binding affinities were calculated for these multiple docking sites and binding modes of each compound. Our results indicate the high affinity of ivermectin, and even higher affinities for some of the other compounds evaluated, for all three of these molecular targets. These results suggest biological mechanisms by which ivermectin may limit the infectivity and morbidity of the SARS-CoV-2 virus and stimulate an α7nAChr-mediated anti-inflammatory pathway that could limit cytokine production by immune cells.

CD147-spike protein interaction in COVID-19: Get the ball rolling with a novel receptor and therapeutic target

The combat against the Corona virus disease of 2019 (COVID-19), has created a chaos among the healthcare institutions and researchers, in turn accelerating the dire need to curtail the infection spread. The already established entry mechanism, via ACE2 has not yet successfully aided in the development of a suitable and reliable therapy. Taking in account the constant progression and deterioration of the cases worldwide, a different perspective and mechanistic approach is required, which has thrown light onto the cluster of differentiation 147 (CD147) transmembrane protein, as a novel route for SARS-CoV-2 entry. Despite lesser affinity towards COVID-19 virus, as compared to ACE2, this receptor provides a suitable justification behind elevated blood glucose levels in infected patients, retarded COVID-19 risk in women, enhanced susceptibility in geriatrics, greater infection susceptibility of T cells, infection prevalence in non-susceptible human cardiac pericytes and so on. The manuscript invokes the title role and distribution of CD147 in COVID-19 as an entry receptor and mediator of endocytosis-promoted entry of the virus, along with the "catch and clump" hypothesis, thereby presenting its Fundamental significance as a therapeutic target for potential candidates, such as Azithromycin, melatonin, statins, beta adrenergic blockers, ivermectin, Meplazumab etc. Thus, the authors provide a comprehensive review of a different perspective in COVID-19 infection, aiming to aid the researchers and virologists in considering all aspects of viral entry, in order to develop a sustainable and potential cure for the 2019 COVID-19 disease.

Erythropoietin therapy in a case of neonatal anemia after exposure to natalizumab throughout pregnancy

Background

Natalizumab is a monoclonal antibody approved for the treatment of patients with relapsing-remitting multiple sclerosis. According to the current clinical recommendations, its use during pregnancy should be carefully evaluated only in women with highly active disease who plan a pregnancy or have an unplanned pregnancy, after accurate counseling about eventual maternal disease relapse due to therapy suspension.

Case presentation

This brief case report describes a case of documented anemia that we observed in a newborn whose mother with relapsing-remitting multiple sclerosis was treated with an extended dosing protocol of natalizumab throughout pregnancy. The newborn received the infusion of erythropoietin every seven days from the fortieth day of life; subsequently, the status of anemia underwent clinical resolution.

Conclusions

This case report confirmed that natalizumab can cause disorders of hematopoiesis, including anemia, thrombocytopenia, or pancytopenia, in newborns of patients treated during pregnancy. A multidisciplinary team, including experienced pediatricians and pediatric hematologists, has a critical role in managing newborns delivered by women, being treated with natalizumab for treating relapsing-remitting multiple sclerosis during pregnancy.

Assessment of Fibrinogen Macromolecules Interaction with Red Blood Cells Membrane by Means of Laser Aggregometry, Flow Cytometry, and Optical Tweezers Combined with Microfluidics

An elevated concentration of fibrinogen in blood is a significant risk factor during many pathological diseases, as it leads to an increase in red blood cells (RBC) aggregation, resulting in hemorheological disorders. Despite the biomedical importance, the mechanisms of fibrinogen-induced RBC aggregation are still debatable. One of the discussed models is the non-specific adsorption of fibrinogen macromolecules onto the RBC membrane, leading to the cells bridging in aggregates. However, recent works point to the specific character of the interaction between fibrinogen and the RBC membrane. Fibrinogen is the major physiological ligand of glycoproteins receptors IIbIIIa (GPIIbIIIa or αIIββ3 or CD41/CD61). Inhibitors of GPIIbIIIa are widely used in clinics for the treatment of various cardiovascular diseases as antiplatelets agents preventing the platelets’ aggregation. However, the effects of GPIIbIIIa inhibition on RBC aggregation are not sufficiently well studied. The objective of the present work was the complex multimodal in vitro study of the interaction between fibrinogen and the RBC membrane, revealing the role of GPIIbIIIa in the specificity of binding of fibrinogen by the RBC membrane and its involvement in the cells’ aggregation process. We demonstrate that GPIIbIIIa inhibition leads to a significant decrease in the adsorption of fibrinogen macromolecules onto the membrane, resulting in the reduction of RBC aggregation. We show that the mechanisms underlying these effects are governed by a decrease in the bridging components of RBC aggregation forces.

Gene coexpression networks analysis of sickle stroke risk

Stroke is one of the most destructive complications of sickle cell disease (SCD), and SCD is also the most common cause of childhood stroke. Sickle cell stroke is complex and has a genetic endothelial basis. Here, we further investigated this genetic basis using weighted gene coexpression network analysis. This systems biology approach revealed the correlation between coexpressed gene modules and sickle stroke risk. The pink module was significantly correlated with stroke risk and genes in this module were mainly related to GO:0044877 (protein-containing complex binding). In addition hub genes were identified through protein-protein interaction enrichment analysis, including CXCR7, VCAM1, CD44, BMP2, SMAD3, BCL2L1, ITPR2, ITPR3, etc. These hub genes were significantly enriched for three Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways including "gastric acid secretion," "pathways in cancer," and "TGF- β signaling pathway." Altogether, our results based on this innovative method provided some novel understanding of the pathology of sickle cell stroke. Hub genes identified in this study could be potential targets for screening and prevention of stroke risk in SCD children.

A new level of complexity in parasite-host interaction: The role of extracellular vesicles

Humans and animals have co-existed with parasites in a battle of constant adaptation to one another. It is becoming increasingly clear that extracellular vesicles (EVs) play important roles in this co-existence and pathology. This chapter reviews the current research on EVs released by protozoa, nematodes, trematodes, and cestodes with a special focus on EVs in parasite life cycles. The environmental changes experienced by the parasite during its life cycle is associated with distinct changes in EV release and content. The function of these EV seems to have a significant influence on parasite pathology and survival in the host by concomitantly modulating host immune responses and triggering parasite differentiation. The role of EVs in communication between the parasites and the host adds a new level of complexity in our understanding of parasite biology, which may be a key to further understand the complexity behind host-parasite interactions and communication. This increased understanding can, in turn, open up new avenues for vaccine, diagnostic, and therapeutic development for a wide variety of diseases such as parasite infection, cancers, and immunological disorders.

Essential arterial hypertension patients present higher cell adhesion forces, contributing to fibrinogen-dependent cardiovascular risk

The increase of erythrocyte aggregation by high fibrinogen levels may be an indicator of cardiovascular risk. γ' fibrinogen variant has been considered as a possible player in enhancing aggregation. Here, we assessed, at the single-cell level, the influence of fibrinogen on erythrocyte aggregation in essential arterial hypertension. We also aimed at understanding how γ' fibrinogen is altered in this disease. Using atomic force microscopy (AFM), we show that the work and force necessary for erythrocyte-erythrocyte detachment is higher for patients than for healthy donors, with these parameters further increasing in both groups when higher fibrinogen concentrations are present. This can be associated with changes in blood flow, due to transient bridging of two erythrocytes by fibrinogen, representing an important cardiovascular risk factor. γ' fibrinogen can influence the increased risk in essential arterial hypertension, as we demonstrate that its levels are significantly increased in these patients' blood. Nevertheless, this cannot be the only cause for the changes observed in the AFM data.

SINCERITIES: inferring gene regulatory networks from time-stamped single cell transcriptional expression profiles

Motivation

Single cell transcriptional profiling opens up a new avenue in studying the functional role of cell-to-cell variability in physiological processes. The analysis of single cell expression profiles creates new challenges due to the distributive nature of the data and the stochastic dynamics of gene transcription process. The reconstruction of gene regulatory networks (GRNs) using single cell transcriptional profiles is particularly challenging, especially when directed gene-gene relationships are desired.

Results

We developed SINCERITIES (SINgle CEll Regularized Inference using TIme-stamped Expression profileS) for the inference of GRNs from single cell transcriptional profiles. We focused on time-stamped cross-sectional expression data, commonly generated from transcriptional profiling of single cells collected at multiple time points after cell stimulation. SINCERITIES recovers directed regulatory relationships among genes by employing regularized linear regression (ridge regression), using temporal changes in the distributions of gene expressions. Meanwhile, the modes of the gene regulations (activation and repression) come from partial correlation analyses between pairs of genes. We demonstrated the efficacy of SINCERITIES in inferring GRNs using in silico time-stamped single cell expression data and single cell transcriptional profiles of THP-1 monocytic human leukemia cells. The case studies showed that SINCERITIES could provide accurate GRN predictions, significantly better than other GRN inference algorithms such as TSNI, GENIE3 and JUMP3. Moreover, SINCERITIES has a low computational complexity and is amenable to problems of extremely large dimensionality. Finally, an application of SINCERITIES to single cell expression data of T2EC chicken erythrocytes pointed to BATF as a candidate novel regulator of erythroid development.

Availability and implementation

MATLAB and R version of SINCERITIES are freely available from the following websites: http://www.cabsel.ethz.ch/tools/sincerities.html and https://github.com/CABSEL/SINCERITIES. The single cell THP-1 and T2EC transcriptional profiles are available from the original publications (Kouno et al., 2013; Richard et al., 2016). The in silico single cell data are available on SINCERITIES websites.

Supplementary information

Supplementary data are available at Bioinformatics online.

Examination of Reticulocytosis among Chronically Transfused Children with Sickle Cell Anemia

Sickle cell anemia (SCA) is an inherited hemolytic anemia with compensatory reticulocytosis. Recent studies have shown that increased levels of reticulocytosis during infancy are associated with increased hospitalizations for SCA sequelae as well as cerebrovascular pathologies. In this study, absolute reticulocyte counts (ARC) measured prior to transfusion were analysed among a cohort of 29 pediatric SCA patients receiving chronic transfusion therapy (CTT) for primary and secondary stroke prevention. A cross-sectional flow cytometric analysis of the reticulocyte phenotype was also performed. Mean duration of CTT was 3.1 ± 2.6 years. Fifteen subjects with magnetic resonance angiography (MRA) -vasculopathy had significantly higher mean ARC prior to initiating CTT compared to 14 subjects without MRA-vasculopathy (427.6 ± 109.0 K/μl vs. 324.8 ± 109.2 K/μl, p<0.05). No significant differences in hemoglobin or percentage sickle hemoglobin (HbS) were noted between the two groups at baseline. Reticulocyte phenotyping further demonstrated that the percentages of circulating immature [CD36(+), CD71(+)] reticulocytes positively correlated with ARC in both groups. During the first year of CTT, neither group had significant reductions in ARC. Among this group of children with SCA, cerebrovasculopathy on MRA at initiation of CTT was associated with increased reticulocytosis, which was not reduced after 12 months of transfusions.

CHANGES IN ERYTHROCYTE SURFACE MARKER CD44 DURING HYPOTHERMIC AND LOW TEMPERATURE STORAGE

We studied the changes in surface marker CD44 in erythrocytes, cryopreserved under the protection of glycerol and PEG–1500, or stored in hypothermic conditions. It was shown that during hypothermic storage the CD44 characteristics in erythrocyte suspension were unchanged within 10 days. In cryopreserved erythrocytes a reduction in CD44–positive cells and in the level of expression of the surface marker were marked. Using PEG–1500 resulted in more pronounced change in erythrocyte CD44 characteristics after freeze–thawing in comparison with glycerol. Removal of cryoprotectants and the loss of a part of cells during the washing process led to the restoration of the CD44 characteristics in freeze–thawed erythrocytes suspension which successfully survived after the stresses. The results indicate that revealed changes in cryopreserved erythrocytes cover only a part of the cells, and they are associated with the instability of the population of erythrocytes with altered CD44 characteristics wherethrough after the removal of cryoprotectants with concomitant hemolysis of unstable cells the CD44 parameters in erythrocyte suspensions recovered. The mechanisms underlying the changes in the parameters of the surface marker CD44 in freeze–thawed erythrocyte may be related to the disruption of intermolecular interactions in the membrane under the influence of physical and chemical environmental factors, followed by the membrane vesiculation with the inclusion of the CD44 into the vesicles.

A sphingosine-1 phosphate agonist (FTY720) limits trauma/hemorrhagic shock-induced multiple organ dysfunction syndrome

BACKGROUND

Trauma/hemorrhagic shock (T/HS) is one of the major consequences of battlefield injury as well as civilian trauma. FTY720 (sphingosine-1-phosphate agonist) has the capability to decrease the activity of the innate and adaptive immune systems and, at the same time, maintain endothelial cell barrier function and vascular homeostasis during stress. For this reason, we hypothesize that FTY720, as part of resuscitation therapy, would limit T/HS-induced multiple organ dysfunction syndrome in a rodent T/HS model.

METHODS

Rats subjected to trauma/sham shock (T/SS) or T/HS (30 mm Hg × 90 min) were administered FTY720 (1 mg/kg) post-T/HS during volume resuscitation. Lung injury (permeability to Evans blue dye), polymorphonuclear leukocyte (PMN) priming (respiratory burst activity), and red blood cell (RBC) rigidity were measured. In addition, lymph duct-cannulated rats were used to quantify the effect of FTY720 on gut injury (permeability and morphology) and the biologic activity of T/HS versus T/SS lymph on PMN-RBC and RBC deformability.

RESULTS

Trauma/hemorrhagic shock-induced increased lung permeability, PMN priming, and RBC rigidity were all abrogated by FTY720. The systemic protective effect of FTY720 was only partially at the gut level, because FTY720 did not prevent T/HS-induced gut injury (morphology or permeability); however, it did abrogate T/HS lymph-induced increased respiratory burst and RBC rigidity.

CONCLUSIONS

FTY720 limited T/HS-induced multiple organ dysfunction syndrome (lung injury, red cell injury, and neutrophil priming) as well as T/HS lymph bioactivity, although it did not limit gut injury.

Abnormal adhesion of red blood cells in polycythemia vera: a prothrombotic effect?

Polycythemia vera (PV) is a myeloproliferative neoplasm (MPN) characterised by the V617F activating mutation in the tyrosine kinase JAK2. PV patients exhibit increased haemoglobin levels and red cell mass because of uncontrolled proliferation of the erythroid lineage. Thrombosis and transformation to acute leukaemia are the major causes of morbidity and mortality in this disease. Increased thrombotic risk in PV patients is multifactorial and complex; it is associated with high levels of haemoglobin, impaired rheology and increased viscosity resulting from erythrocytosis. An additional parameter that might contribute to this risk was recently brought to light by work from our group showing abnormal activation of adhesion proteins in PV RBCs. In this review we provide an overview of these recent findings and discuss how the pro-adhesive features of JAK2V617F-positive red blood cells might initiate and contribute to the circulatory complications described in PV.

Diagnostic morphology: biophysical indicators for iron-driven inflammatory diseases

Most non-communicable diseases involve inflammatory changes in one or more vascular systems, and there is considerable evidence that unliganded iron plays major roles in this. Most studies concentrate on biochemical changes, but there are important biophysical correlates. Here we summarize recent microscopy-based observations to the effect that iron can have major effects on erythrocyte morphology, on erythrocyte deformability and on both fibrinogen polymerization and the consequent structure of the fibrin clots formed, each of which contributes significantly and negatively to such diseases. We highlight in particular type 2 diabetes mellitus, ischemic thrombotic stroke, systemic lupus erythematosus, hereditary hemochromatosis and Alzheimer's disease, while recognizing that many other diseases have co-morbidities (and similar causes). Inflammatory biomarkers such as ferritin and fibrinogen are themselves inflammatory, creating a positive feedback that exacerbates disease progression. The biophysical correlates we describe may provide novel, inexpensive and useful biomarkers of the therapeutic benefits of successful treatments.

AKAP-dependent modulation of BCAM/Lu adhesion on normal and sickle cell disease RBCs revealed by force nanoscopy

Human normal and sickle red blood cells (RBCs) adhere with high affinity to the alpha5 chain of laminin (LAMA5) via the basal cell adhesion molecule/Lutheran (BCAM/Lu) receptor, which is implicated in vasoocclusive episodes in sickle cell disease and activated through the cyclic adenosine monophosphate (cAMP) signaling pathway. However, the effect of the cAMP pathway on the expression of active BCAM/Lu receptors at the single-molecule level is unknown. We established an in vitro technique, based on atomic force microscopy, which enables detection of single BCAM/Lu proteins on the RBC surface and measures the unbinding force between BCAM/Lu and LAMA5. We showed that the expression of active BCAM/Lu receptors is higher in homozygous sickle RBCs (SS-RBCs) than normal RBCs and that it is critically dependent on the cAMP signaling pathway on both normal and SS-RBCs. Of importance, we illustrated that A-kinase anchoring proteins are crucial for BCAM/Lu receptor activation. Furthermore, we found that SS-RBCs from hydroxyurea-treated patients show a lower expression of active BCAM/Lu receptors, a lower unbinding force to LAMA5, and insignificant stimulation by epinephrine as compared to SS-RBCs from untreated patients. To our knowledge, these findings may lead to novel antiadhesive targets for vasoocclusive episodes in sickle cell disease.

Single-cell force spectroscopy as a technique to quantify human red blood cell adhesion to subendothelial laminin

Single-cell force spectroscopy (SCFS), an atomic force microscopy (AFM)-based assay, enables quantitative study of cell adhesion while maintaining the native state of surface receptors in physiological conditions. Human healthy and pathological red blood cells (RBCs) express a large number of surface proteins which mediate cell-cell interactions, or cell adhesion to the extracellular matrix. In particular, RBCs adhere with high affinity to subendothelial matrix laminin via the basal cell adhesion molecule and Lutheran protein (BCAM/Lu). Here, we established SCFS as an in vitro technique to study human RBC adhesion at baseline and following biochemical treatment. Using blood obtained from healthy human subjects, we recorded adhesion forces from single RBCs attached to AFM cantilevers as the cell was pulled-off of substrates coated with laminin protein. We found that an increase in the overall cell adhesion measured via SCFS is correlated with an increase in the resultant total force measured on 1 µm(2) areas of the RBC membrane. Further, we showed that SCFS can detect significant changes in the adhesive response of RBCs to modulation of the cyclic adenosine monophosphate (cAMP) and protein kinase A (PKA) pathway. Lastly, we identified variability in the RBC adhesion force to laminin amongst the human subjects, suggesting that RBCs maintain diverse levels of active BCAM/Lu adhesion receptors. By using single-cell measurements, we established a powerful new method for the quantitative measurement of single RBC adhesion with specific receptor-mediated binding.

Trauma-hemorrhagic shock induces a CD36-dependent RBC endothelial-adhesive phenotype

OBJECTIVE

Microvascular dysfunction is a key element in the development of the multiple organ dysfunction syndrome. Although the mechanisms for this response are unclear, RBC adhesion to endothelium may initiate intravascular occlusion leading to ischemic tissue injury. Thus, we tested the hypothesis that trauma-hemorrhage induces RBC-endothelial cell adhesion.

DESIGN

Prospective in vivo and in vitro animal study and analysis of patient blood samples.

SETTING

University research laboratory and hospital emergency and trauma units.

INTERVENTION

We initially assayed RBC adhesion to endothelial cells in vitro using RBCs obtained from rats subjected to trauma-hemorrhagic shock or sham shock as well as from severely injured trauma patients. Subsequently, we measured the role of putative RBCs and endothelial cell receptors in the increased RBC-endothelial cell adhesive response.

MAIN RESULTS

In both rats and humans, trauma-hemorrhagic shock increased RBC adhesion to endothelium as well as increasing several putative RBC surface adhesion molecules including CD36. The critical factor leading to RBC-endothelial cell adhesion was increased surface RBC CD36 expression. Adhesion of trauma-hemorrhagic shock RBCs was mediated, at least in part, by the binding of RBC CD36 to its cognate endothelial receptors (αVβ3 and VCAM-1). Gut-derived factors carried in the intestinal lymphatics triggered these trauma-hemorrhagic shock-induced RBC changes because 1) preventing trauma-hemorrhagic shock intestinal lymph from reaching the systemic circulation abrogated the RBC effects, 2) in vitro incubation of naïve whole blood with trauma-hemorrhagic shock lymph replicated the in vivo trauma-hemorrhagic shock-induced RBC changes while 3) injection of trauma-hemorrhagic shock lymph into naïve animals recreated the RBC changes observed after actual trauma-hemorrhagic shock.

CONCLUSIONS

1) Trauma-hemorrhagic shock induces rapid RBC adhesion to endothelial cells in patients and animals. 2) Increased RBC CD36 expression characterizes the RBC-adhesive phenotype. 3) The RBC phenotypic and functional changes were induced by gut-derived humoral factors. These novel findings may explain the microvascular dysfunction occurring after trauma-hemorrhagic shock, sepsis, and other stress states.

Cellular adhesion and the endothelium: P-selectin

P-selectin on endothelial cell surfaces is central to impaired microvascular blood flow in sickle cell disease (SCD). Restoration of blood flow is expected to provide therapeutic benefit for SCD patients, whatever the mechanism of action of the treatment. Long-term oral administration of a P-selectin-blocking agent potentially improves blood flow and averts acute painful vaso-occlusive crises in patients with SCD. This review focuses on the pathophysiology of the impairment of microvascular blood flow in SCD with an emphasis on the role of P-selectin and summarizes the status of development of antiselectin therapies as a means of improving microvascular flow.

Role of red blood cell flow behavior in hemodynamics and hemostasis

The primary role of red blood cells (RBCs) is to transport oxygen to the tissues, which is performed predominantly in the blood capillaries. However, RBCs have unique flow-affecting properties that play a key role in blood flow in all blood vessel types and sizes. While RBCs as oxygen carriers have been studied extensively, their hemodynamic function has been examined less comprehensively. This review aims to bridge this gap, focusing on the role of RBC flow properties in hemodynamics, hemostasis and thrombosis.

Altered red cell and platelet adhesion in hemolytic diseases: Hereditary spherocytosis, paroxysmal nocturnal hemoglobinuria and sickle cell disease

OBJECTIVES

Intravascular hemolysis may have important pathophysiological consequences, such as the induction of cellular adhesion and vasculopathy. We compared the adhesive properties of red cells (RBC) and platelets in hereditary spherocytosis (HS), paroxysmal nocturnal hemoglobinuria (PNH) and sickle cell disease (SCD) patients.

DESIGN AND METHODS

The adhesion of RBC and platelets, from patients and healthy subjects, was determined using static adhesion assays. RBC surface markers were characterized by flow cytometry and lactate dehydrogenase (LDH), plasma hemoglobin (pHb) and TNF-α were assayed in serum/plasma samples.

RESULTS

pHb levels were elevated in all three hemolytic diseases, indicating the incidence of intravascular hemolysis. RBC adhesion and TNF-α were augmented in HS and SCD, but not in PNH. Reticulocyte counts were raised in the three diseases, but were higher in HS and SCD than in PNH; high expressions of CD71, CD36 and CD49d were observed on SCD RBC, while CD71 alone was increased on HS and PNH RBC. Splenectomy was associated with reversals of increased pHb, RBC adhesion, reticulocytes, RBC marker expression and inflammation in HS. In contrast, platelet adhesion was elevated in SCD and PNH, but not HS. Platelet adhesion correlated significantly with serum LDH, but not pHb, in the hemolytic disease cohort; interestingly, LDH did not correlate with reticulocytes or pHb levels.

CONCLUSIONS

Results indicate that extravascular, rather than intravascular, hemolysis (and ensuing RBC production) may contribute to elevations in RBC adhesive properties in HS and SCD, while mechanisms peculiar to each disease may augment platelet adhesion in SCD and PNH.

The promise of fetal cells in maternal blood

Delaying childbirth increases the proportion of advanced maternal age pregnancies. This increases the number of pregnancies requiring invasive prenatal testing. Prenatal diagnosis of chromosomal aneuploidies and monogenic disorders requires fetal cells obtained through invasive procedures (i.e. chorionic villus sampling and amniocentesis). These procedures carry a risk of fetal loss, which causes anxiety to at-risk couples. Intact fetal cells entering maternal circulation have raised the possibility of non-invasive prenatal diagnosis. Rarity of fetal cells, however, has made it challenging. Fetal nucleated red blood cells are ideal candidate target cells because they have limited lifespan, contain true representation of fetal genotype, contain specific fetal cell identifiers (embryonic and fetal globins), and allow interrogation with chromosomal fluorescence in-situ hybridisation and possibly with array comparative genomic hybridisation. The utility of fetal nucleated red blood cells in non-invasive prenatal diagnosis has not reached clinical application because of the inconsistencies in enrichment strategies and rarity of cells.

Expression profiling reveals novel hypoxic biomarkers in peripheral blood of adult mice exposed to chronic hypoxia

Hypoxia induces a myriad of changes including an increase in hematocrit due to erythropoietin (EPO) mediated erythropoiesis. While hypoxia is of importance physiologically and clinically, lacunae exist in our knowledge of the systemic and temporal changes in gene expression occurring in blood during the exposure and recovery from hypoxia. To identify these changes expression profiling was conducted on blood obtained from cohorts of C57Bl-10 wild type mice that were maintained at normoxia (NX), exposed for two weeks to normobaric chronic hypoxia (CH) or two weeks of CH followed by two weeks of normoxic recovery (REC). Using stringent bioinformatic cut-offs (0% FDR, 2 fold change cut-off), 230 genes were identified and separated into four distinct temporal categories. Class I) contained 1 transcript up-regulated in both CH and REC; Class II) contained 202 transcripts up-regulated in CH but down-regulated after REC; Class III) contained 9 transcripts down-regulated both in CH and REC; Class IV) contained 18 transcripts down-regulated after CH exposure but up-regulated after REC. Profiling was independently validated and extended by analyzing expression levels of selected genes as novel biomarkers from our profile (e.g. spectrin alpha-1, ubiquitin domain family-1 and pyrroline-5-carboxylate reductase-1) by performing qPCR at 7 different time points during CH and REC. Our identification and characterization of these genes define transcriptome level changes occurring during chronic hypoxia and normoxic recovery as well as novel blood biomarkers that may be useful in monitoring a variety of physiological and pathological conditions associated with hypoxia.

Chitosan-based ultrathin films as antifouling, anticoagulant and antibacterial protective coatings

Ultrathin antifouling and antibacterial protective nanocoatings were prepared from ionic derivatives of chitosan using layer-by-layer deposition methodology. The surfaces of silicon, and glass protected by these nanocoatings were resistant to non-specific adsorption of proteins disregarding their net charges at physiological conditions (positively charged TGF-β1 growth factor and negatively charged bovine serum albumin) as well as human plasma components. The coatings also preserved surfaces from the formation of bacterial (Staphylococcus aureus) biofilm as shown using microscopic studies (SEM, AFM) and the MTT viability test. Moreover, the chitosan-based films adsorbed onto glass surface demonstrated the anticoagulant activity towards the human blood. The antifouling and antibacterial actions of the coatings were correlated with their physicochemical properties. The studied biologically relevant properties were also found to be dependent on the thickness of those nanocoatings. These materials are promising for biomedical applications, e.g., as protective coatings for medical devices, anticoagulant coatings and protective layers in membranes.

Suppressive effects of aluminum trichloride on the T lymphocyte immune function of rats

Aluminum (Al) has increasingly been used in the daily life, and could cause the change of human health because it can accumulate in the organs. A rat model was thus used to examine potential effect of Al on the immune function. Forty male Wistar rats (5 weeks old) weighed 110-120 g were randomly allocated into four groups and were orally exposed to 0, 64.18, 128.36, and 256.72 mg/kg body weight aluminum trichloride (AlCl3) in drinking water for 120 days. The levels of CD3+, CD4+, CD8+ T lymphocyte, acid non-specific activity esterase (ANAE+) in blood, and interleukin-2 (IL-2) and tumor necrosis factor-α (TNF-α) in serum were determined at the end of experiment. The results showed that the proportions of CD3+, CD4+ T lymphocyte, the ratio of CD4+/CD8+, and the levels of ANAE+, IL-2, and TNF-α were significantly reduced in AlCl3-treated rats, while the proportion of CD8+ T lymphocyte was increased in an AlCl3-dose dependent manner. Our findings indicate that a long term exposure of AlCl3 could suppress the T lymphocyte immune function of rats.

Regulation of phosphatidylserine exposure in red blood cells

The exposure of phosphatidylserine (PS) on the outer membrane leaflet of red blood cells (RBCs) serves as a signal for eryptosis, a mechanism for the RBC clearance from blood circulation. The process of PS exposure was investigated as function of the intracellular Ca(2+) content and the activation of PKCα in human and sheep RBCs. Cells were treated with lysophosphatidic acid (LPA), 4-bromo-A23187, or phorbol-12 myristate-13 acetate (PMA) and analysed by flow cytometry, single cell fluorescence video imaging, or confocal microscopy. For human RBCs, no clear correlation existed between the number of cells with an elevated Ca(2+) content and PS exposure. Results are explained by three different mechanisms responsible for the PS exposure in human RBCs: (i) Ca(2+)-stimulated scramblase activation (and flippase inhibition) by LPA, 4-bromo-A23187, and PMA; (ii) PKC activation by LPA and PMA; and (iii) enhanced lipid flop caused by LPA. In sheep RBCs, only the latter mechanism occurs suggesting absence of scramblase activity.

Integrin-associated protein (CD47) is a putative mediator for soluble fibrinogen interaction with human red blood cells membrane

Fibrinogen is a multifunctional plasma protein that plays a crucial role in several biological processes. Elevated fibrinogen induces erythrocyte hyperaggregation, suggesting an interaction between this protein and red blood cells (RBCs). Several studies support the concept that fibrinogen interacts with RBC membrane and this binding, due to specific and non-specific mechanisms, may be a trigger to RBC hyperaggregation in inflammation. The main goals of our work were to prove that human RBCs are able to specifically bind soluble fibrinogen, and identify membrane molecular targets that could be involved in this process. RBCs were first isolated from blood of healthy individuals and then separated in different age fractions by discontinuous Percoll gradients. After isolation RBC samples were incubated with human soluble fibrinogen and/or with a blocking antibody against CD47 followed by fluorescence confocal microscopy, flow cytometry acquisitions and zeta potential measurements. Our data show that soluble fibrinogen interacts with the human RBC membrane in an age-dependent manner, with younger RBCs interacting more with soluble fibrinogen than the older cells. Importantly, this interaction is abrogated in the presence of a specific antibody against CD47. Our results support a specific and age-dependent interaction of soluble fibrinogen with human RBC membrane; additionally we present CD47 as a putative mediator in this process. This interaction may contribute to RBC hyperaggregation in inflammation.

RNA aptamer therapy for vaso-occlusion in sickle cell disease

Patients with sickle cell disease (SCD) often suffer painful vaso-occlusive episodes caused in part by the adhesion of sickle erythrocytes (SS-RBC) to the vascular endothelium. To investigate inhibition of SS-RBC adhesion as a possible treatment for vaso-occlusion, 2 adhesion molecules, α(v)β(3) and P-selectin, were targeted by high-affinity RNA aptamers. An in vitro flow chamber assay was used to test the antiadhesion activity of α(v)β(3) aptamer clone 17.16. Human SS-RBC were passed across a confluent monolayer of thrombin-stimulated human umbilical vein endothelial cells (HUVEC) at a constant rate. α(v)β(3) aptamer reduced SS-RBC adhesion to activated endothelial cells to the level seen with untreated HUVEC. An aptamer reactive with complement component 8 was used as a negative control and exerted no inhibition, confirming the specificity of α(v)β(3) aptamer (P=0.04). At 2 dyn/cm(2) shear stress, 30 nM α(v)β(3) aptamer showed maximal effect in decreasing SS-RBC adhesion to HUVEC. The antiadhesive activity of the P-selectin aptamer clone PF377 was also tested using HUVEC pretreated with IL-13 to upregulate expression of P-selectin as seen in activated endothelial cells. At 1 dyn/cm(2) shear stress, 60 nM of P-selectin aptamer had antiadhesion activity similar to heparin, a known inhibitor of SS-RBC adhesion to P-selectin. A negative control did not prevent adhesion (P=0.05). These data show the potential utility of aptamers to block endothelial adhesion molecules to prevent or treat vaso-occlusion in SCD.

Results from transcranial Doppler examination on children and adolescents with sickle cell disease and correlation between the time-averaged maximum mean velocity and hematological characteristics: a cross-sectional analytical study

CONTEXT AND OBJECTIVE

Transcranial Doppler (TCD) detects stroke risk among children with sickle cell anemia (SCA). Our aim was to evaluate TCD findings in patients with different sickle cell disease (SCD) genotypes and correlate the time-averaged maximum mean (TAMM) velocity with hematological characteristics.

DESIGN AND SETTING

Cross-sectional analytical study in the Pediatric Hematology sector, Universidade Federal de São Paulo.

METHODS

85 SCD patients of both sexes, aged 2-18 years, were evaluated, divided into: group I (62 patients with SCA/Sß(0) thalassemia); and group II (23 patients with SC hemoglobinopathy/Sß(+) thalassemia). TCD was performed and reviewed by a single investigator using Doppler ultrasonography with a 2 MHz transducer, in accordance with the Stroke Prevention Trial in Sickle Cell Anemia (STOP) protocol. The hematological parameters evaluated were: hematocrit, hemoglobin, reticulocytes, leukocytes, platelets and fetal hemoglobin. Univariate analysis was performed and Pearson's coefficient was calculated for hematological parameters and TAMM velocities (P < 0.05).

RESULTS

TAMM velocities were 137 ± 28 and 103 ± 19 cm/s in groups I and II, respectively, and correlated negatively with hematocrit and hemoglobin in group I. There was one abnormal result (1.6%) and five conditional results (8.1%) in group I. All results were normal in group II. Middle cerebral arteries were the only vessels affected.

CONCLUSION

There was a low prevalence of abnormal Doppler results in patients with sickle-cell disease. Time-average maximum mean velocity was significantly different between the genotypes and correlated with hematological characteristics.

Erythroid adhesion molecules in sickle cell disease: effect of hydroxyurea

In sickle cell disease, the complex scenario of vaso-occlusive crisis (VOC) typical of this disease is clearly multifactorial and not fully understood. Cell-cell and cell-cell matrix interactions mediated by adhesive molecules present on blood cells and endothelial cells (ECs) are thought to play an important role. Early studies have shown that sickle red blood cells (RBCs) are abnormally adherent to ECs and some of the molecules involved in these interactions have been identified, such as the alpha4beta1 integrin and CD36, exclusively present on stress reticulocytes, and CD47 on mature RBCs. More recently, attention focused on Lu/BCAM, the unique RBC receptor for laminin, and on ICAM-4, a red cell-specific adhesion receptor, which is a ligand for a large repertoire of integrins (alphaLbeta2, alphaMbeta2, alphaxbeta2, alphaVbeta3). The counter-receptors on ECs and the role of plasma proteins forming bridges between blood cells and ECs have been clarified in part. It has also been shown that reticulocytes from SCD patients express higher levels of alpha4beta1 integrin and CD36, and that under hydroxyurea (HU) therapy, both cell adhesion to ECs or extracellular matrix proteins and the levels of these adhesion molecules are reduced. These findings are consistent with the view that enhanced adhesion of blood cells to ECs is largely determined by the membrane expression level of adhesion molecules and could be a crucial factor for triggering or aggravating vaso-occlusion. In SCD patients, membrane expression of Lu/BCAM (and perhaps ICAM-4) is enhanced on RBCs whose adherence to laminin or ECs is also increased. Interestingly, Lu/BCAM- and ICAM-4-mediated adhesion are enhanced by the stress mediator epinephrine through a PKA-dependent pathway initiated by a rise in intracellular cAMP and leading to receptor activation by phosphorylation according to the same signaling pathway. More recently, studies based on quantitative expression analysis of adhesion molecules on RBCs and during erythroid differentiation in patients undergoing HU therapy, surprisingly revealed that Lu/BCAM level was enhanced, although alpha4beta1, CD36 and ICAM-4 (to a lower extent) levels were indeed reduced. CD47 and CD147 expression were also enhanced in HU-treated patients. Based on these findings we suggest that the signalization cascade leading to receptor activation rather than the expression level only of adhesion molecules may be the critical factor regulating cell adhesion, although both mechanisms are not mutually exclusive.

Red-cell ICAM-4 is a ligand for the monocyte/macrophage integrin CD11c/CD18: characterization of the binding sites on ICAM-4

Intercellular adhesion molecule 4 (ICAM-4) is a unique member of the ICAM family because of its specific expression on erythroid cells and ability to interact with several types of integrins expressed on blood and endothelial cells. The first reported receptors for ICAM-4 were CD11a/CD18 and CD11b/CD18. In contrast to these 2, the cellular ligands and the functional role of the third beta2 integrin, CD11c/CD18, have not been well defined. Here, we show that ICAM-4 functions as a ligand for the monocyte/macrophage-specific CD11c/CD18. Deletion of the individual immunoglobulin domains of ICAM-4 demonstrated that both its domains contain binding sites for CD11c/CD18. Analysis of a panel of ICAM-4 point mutants identified residues that affected binding to the integrin. By molecular modeling the important residues were predicted to cluster in 2 distinct but spatially close regions of the first domain with an extension to the second domain spatially distant from the other residues. We also identified 2 peptides derived from sequences of ICAM-4 that are capable of modulating the binding to CD11c/CD18. CD11c/CD18 is expressed on macrophages in spleen and bone marrow. Inhibition of erythrophagocytosis by anti-ICAM-4 and anti-integrin antibodies suggests a role for these interactions in removal of senescent red cells.

Maturation and enucleation of primitive erythroblasts during mouse embryogenesis is accompanied by changes in cell-surface antigen expression

Primitive erythroblasts (EryPs) are the first hematopoietic cell type to form during mammalian embryogenesis and emerge within the blood islands of the yolk sac. Large, nucleated EryPs begin to circulate around midgestation, when connections between yolk sac and embryonic vasculature mature. Two to 3 days later, small cells of the definitive erythroid lineage (EryD) begin to differentiate within the fetal liver and rapidly outnumber EryPs in the circulation. The development and maturation of EryPs remain poorly defined. Our analysis of embryonic blood at different stages reveals a stepwise developmental progression within the EryP lineage from E9.5 to E12.5. Thereafter, EryDs are also present in the bloodstream, and the 2 lineages are not easily distinguished. We have generated a transgenic mouse line in which the human epsilon-globin gene promoter drives expression of green fluorescent protein exclusively within the EryP lineage. Here, we have used this line to characterize changes in cell morphology and surface-marker expression as EryPs mature and to track EryP numbers and enucleation throughout gestation. This study identifies previously unrecognized synchronous developmental stages leading to the maturation of EryPs in the mouse embryo. Unexpectedly, we find that EryPs are a stable cell population that persists through the end of gestation.

Red blood cell age determines the impact of storage and leukocyte burden on cell adhesion molecules, glycophorin A and the release of annexin V

The influence of the age of the red blood cell (RBC) within its 120-day lifecycle at the time of blood donation on the RBC storage lesion is not well understood. Expression of cell adhesion molecules (CAMs) (CD44, CD47, CD58 and CD147), glycophorin A (GPA) and phosphatidylserine (PS) on young and old RBCs density separated prior to storage of the RBC concentrate was determined by flow cytometry. Older RBCs showed significantly reduced expression of GPA throughout storage and CD44 and CD147 from Day 28 onwards compared to young RBCs. Storage in the presence of leukocytes caused a significant decline in the expression of CD44, CD58, CD147 and GPA, whereas RBCs that were pre-storage leukocyte depleted maintained a relatively consistent level of expression throughout storage. PS was not detected at the external RBC membrane of young or old RBCs during storage. Increased levels of annexin V were detected in the supernatant of RBCs stored in the presence of leukocytes, with significantly greater supernatant levels found for old RBCs compared to young RBCs. These findings provide new insight into the RBC storage lesion and indicate that RBC age at the time of donation impacts upon the quality of stored RBC concentrates.

Protein kinase A-dependent phosphorylation of Lutheran/basal cell adhesion molecule glycoprotein regulates cell adhesion to laminin alpha5

Lutheran (Lu) blood group and basal cell adhesion molecule (B-CAM) antigens reside on two glycoprotein (gp) isoforms Lu and Lu(v13) that belong to the Ig superfamily and differ only by the size of their cytoplasmic tail. Lu/B-CAM gps have been recognized as laminin alpha5 receptors on red blood cells and epithelial cells in multiple tissues. It has been shown that sickle red cells exhibit enhanced adhesion to laminin alpha5 when intracellular cAMP is up-regulated by physiological stimuli such as epinephrine and that this signaling pathway is protein kinase A- and Lu/B-CAM-dependent. In this study, we analyzed the relationship between the phosphorylation status of Lu/B-CAM gps and their adhesion function to laminin alpha5. We showed that Lu isoform was phosphorylated in sickle red cells as well as in erythroleukemic K562 and epithelial Madin-Darby canine kidney cells and that this phosphorylation is enhanced by different stimuli of the PKA pathway. Lu gp is phosphorylated by glycogen synthase kinase 3 beta, casein kinase II, and PKA at serines 596, 598, and 621, respectively. Alanine substitutions of serines 596 and 598 abolished phosphorylation by glycogen synthase kinase 3 beta and casein kinase II, respectively, but had no effect on adhesion of K562 cells to laminin under flow conditions. Conversely, mutation of serine 621 prevented phosphorylation by PKA and dramatically reduced cell adhesion. Furthermore, stimulation of K562 cells by epinephrine increased Lu gp phosphorylation by PKA and enhanced adhesion to laminin. It is postulated that modulation of the phosphorylation state of Lu gp might be a critical factor for the sickle red cells adhesiveness to laminin alpha5 in sickle cell disease.

Basigin (CD147) is the target for organomercurial inhibition of monocarboxylate transporter isoforms 1 and 4: the ancillary protein for the insensitive MCT2 is EMBIGIN (gp70)

Translocation of monocarboxylate transporters MCT1 and MCT4 to the plasma membrane requires CD147 (basigin) with which they remain tightly associated. However, the importance of CD147 for MCT activity is unclear. MCT1 and MCT4 are both inhibited by the cell-impermeant organomercurial reagent p-chloromercuribenzene sulfonate (pCMBS). Here we demonstrate by site-directed mutagenesis that removal of all accessible cysteine residues on MCT4 does not prevent this inhibition. pCMBS treatment of cells abolished co-immunoprecipitation of MCT1 and MCT4 with CD147 and enhanced labeling of CD147 with a biotinylated-thiol reagent. This suggested that CD147 might be the target of pCMBS, and further evidence for this was obtained by treatment of cells with the bifunctional organomercurial reagent fluorescein dimercury acetate that caused oligomerization of CD147. Site-directed mutagenesis of CD147 implicated the disulfide bridge in the Ig-like C2 domain of CD147 as the target of pCMBS attack. MCT2, which is pCMBS-insensitive, was found to co-immunoprecipitate with gp70 rather than CD147. The interaction between gp70 and MCT2 was confirmed using fluorescence resonance energy transfer between the cyan fluorescent protein- and yellow fluorescent protein-tagged MCT2 and gp70. pCMBS strongly inhibited lactate transport into rabbit erythrocytes, where MCT1 interacts with CD147, but not into rat erythrocytes where it interacts with gp70. These data imply that inhibition of MCT1 and MCT4 activity by pCMBS is mediated through its binding to CD147, whereas MCT2, which associates with gp70, is insensitive to pCMBS. We conclude that ancillary proteins are required to maintain the catalytic activity of MCTs as well as for their translocation to the plasma membrane.

Expansion of CD34 + Cells on Telomerized Human Stromal Cells without Losing Erythroid-Differentiation Potential in a Serum-Free Condition

Erythropoiesis progresses from stem cell expansion on stromal cells through the formation of an erythroblastic island. Our aim was to assess the feasibility of using human stromal cells for erythroid production and differentiation. When cord blood CD34+ cells were cocultured with telomerized human stromal cells (hTERT-stromal cells) for 2 weeks, the CD34+ cells and burst-forming units-erythroid (BFU-E) significantly expanded, and a few hematopoietic cells transmigrated below the stromal layer. When nonadherent hematopoietic progenitor cells that had expanded above the hTERT-stromal cells (group B) were collected and subjected to our erythroid-differentiation protocol, they differentiated into erythroblasts with a slight hemoglobin synthesis. When the few hematopoietic cells that had transmigrated below the stromal layer were expanded for an additional 2 to 6 weeks, they exhibited a cobblestone-like appearance, and a large amount of BFU-E clambered weekly from the underside of the stromal layer to above the stromal layer (group C). When the hematopoietic progenitor cells in group C were subjected to the erythroid-differentiation protocol, large numbers of mature erythroblasts (more than 300,000 times the initial CD34+ cell number) were produced. Our hTERT-stromal expansion protocol may contribute to the construction of a system for large-scale, long-term production of erythroid cells.

The red blood cell and vascular function in health and disease

Nitric oxide (NO) is widely accepted as a central regulator of vascular tone and a vast array of other cardiovascular signaling mechanisms. An emerging player in these mechanisms is hemoglobin (Hb), an erythrocytic protein that serves as the archetypical model for an allosteric protein. Specifically, red blood cells (RBC) are suggested to be integral in matching blood flow to tissue oxygen demands. The mechanisms proposed involve the ability of Hb to sense changes in oxygen concentrations and coupling this process to modulating vascular NO levels. The molecular basis of these mechanisms remains under investigation, but is clearly diverse and discussed in this article from the basis of the blood flow responses to hypoxia. Another emerging theme in RBC biology is the role of these cells during inflammatory disease in which disease processes promote the interaction of vascular NO and the RBC. This is exemplified in hemolytic diseases, in which released Hb has drastic affects on vascular homeostasis mechanisms. Additionally, it is becoming evident that RBC express numerous molecules that mediate interactions with the extracellular matrix and cellular mediators of inflammation. The functional implications for such interactions remain unclear but highlight potential roles of the RBC in modulating inflammatory disease.

Sickle red blood cells accumulate in tumor

The preferential accumulation of sickle blood cells in tumor vasculature is demonstrated noninvasively using MRI and sickle red blood cells loaded with Gd-DTPA and invasively by two other techniques. The distribution of red blood cells in rat brain tumors relative to normal brains were measured using three separate techniques: MRI of Gd-DTPA loaded cells, fluorescent microscopy detection of Oregon Green 488 fluorescence conjugated to a streptavidin-biotin complex that binds to red blood cell surface proteins, and autoradiography using a technetium (99m)Tc-labeling kit. Labeled red cells were infused intravenously in rats with brain tumors. Sickle cells preferentially accumulated in tumor relative to normal brain, with highest concentrations near the tumor / normal tissue boundary, whereas control normal red cells did not preferentially aggregate at the tumor periphery. This demonstrates the potential of sickle red blood cells to accumulate in the abnormal tumor vessel network, and the ability to detect their aggregation noninvasively and at high spatial resolution using MRI. The application of the noninvasive measurement of sickle cells for imaging tumor neovasculature, or as a delivery tool for therapy, requires further study.

Placenta growth factor activates monocytes and correlates with sickle cell disease severity

Sickle cell disease (SCD) results in chronic hypoxia and secondarily increased erythropoietin concentrations. Leukocytosis and activated monocytes are also observed in SCD in absence of infection or vaso-occlusion (steady state), the reasons for which are unknown. We found that erythroid cells produced placenta growth factor (PlGF), an angiogenic growth factor belonging to the vascular endothelial growth factor (VEGF) family, and its expression was induced in bone marrow CD34+ progenitor cells in the presence of erythropoietin. Furthermore, the steady state circulating PlGF levels in subjects with severe SCD (at least 3 vaso-occlusive crises [VOCs] per year) were 18.5 +/- 1.2 pg/mL (n = 9) compared with 15.5 +/- 1.2 pg/mL (n = 13) in those with mild SCD (fewer than 3 VOCs per year) and 11.3 +/- 0.7 pg/mL (n = 9) in healthy controls (P <.05), suggesting a correlation between PlGF levels and SCD severity. In addition, PlGF significantly increased mRNA levels of the proinflammatory cytochemokines interleukin-1beta, interleukin-8, monocyte chemoattractant protein-1, and VEGF in peripheral blood mononuclear cells (MNCs) of healthy subjects (n = 4; P <.05). Expression of these same cytochemokines was significantly increased in MNCs from subjects with SCD at steady state (n = 14), compared with healthy controls. Of the leukocyte subfractions, PlGF stimulated monocyte chemotaxis (P <.05, n = 3). Taken together, these data show for the first time that erythroid cells intrinsically release a factor that can directly activate monocytes to increase inflammation. The baseline inflammation seen in SCD has always been attributed to sequelae secondary to the sickling phenomenon. We show that PlGF contributes to the inflammation observed in SCD and increases the incidence of vaso-occlusive events.

Red blood cells promote survival and cell cycle progression of human peripheral blood T cells independently of CD58/LFA-3 and heme compounds

Red blood cells (RBC) are known to modulate T cell proliferation and function possibly through downregulation of oxidative stress. By examining parameters of activation, division, and cell death in vitro, we show evidence that the increase in survival afforded by RBC is due to the maintenance of the proliferative capacity of the activated T cells. We also show that the CD3+CD8+ T cell subset was preferentially expanded and rescued from apoptosis both in bulk peripheral blood lymphocyte cultures and with highly purified CD8+ T cells. The ability of RBC to induce survival of dividing T cells was not affected by blocking the CD58/CD2 interaction. Moreover, addition of hemoglobin, heme or protoporphyrin IX to cultures of activated T cells did not reproduce the effect of intact RBC. Considering that RBC circulate throughout the body, they could play a biological role in the modulation of T cell differentiation and survival in places of active cell division. Neither CD58 nor the heme compounds studied seem to play a direct relevant role in the modulation of T cell survival.

Intermittent flow increases endotoxin-induced adhesion of human erythrocytes to vascular endothelial cells

OBJECTIVE

To investigate the effects of different conditions of flow on endotoxin induced adhesion of human red blood cells (RBC) to human umbilical vein endothelial cells (HUVEC).

DESIGN AND SETTING

Prospective, randomized, controlled in vitro study in a university-affiliated cell biology laboratory. SUBJECTS. Human erythrocytes, human vascular endothelial cells.

INTERVENTIONS

Superfusion of HUVEC monolayers with human erythrocytes incubated with either saline (CON) or endotoxin (ETX) with different flow pattern (basic flow rates of 0.65 or 1.3 ml/min; intermittent flow, IMF). The CON/0.6, CON/1.3, CON-IMF/1.3 ( n=7/group) groups served as control, and in test groups ETX/0.6, ETX/1.3, ETX-IMF/0.6, and ETX-IMF/1.3 ( n=7/group) both RBC and HUVECs were incubated with ETX and flow pattern and rates varied. In the IMF experiments flow rates of 0.65 and 1.3 ml/min were combined with stop-and-go flow pattern.

MEASUREMENTS AND RESULTS

At continuous flow of 0.65 ml/min erythrocyte adhesion was 61+/-5 cells/mm(2) in CON and 172+/-25 cells/mm(2) after ETX. When flow rate was increased to 1.3 ml/min, adhesion decreased to 27+/-4 cells/mm(2) in CON and 93+/-18 cells/mm(2) after ETX. IMF conditions had no effect on RBC adhesion of naive RBC but increased the number of adhesive erythrocytes after incubation with ETX both at 0.65 ml/min (287+/-33 cells/mm(2)) and at 1.3 ml/min (148+/-13 cells/mm(2)).

CONCLUSIONS

RBC adhesion to vascular endothelium is affected by rate and pattern of blood flow. Higher flow rates or shear forces reduce RBC adhesion while stop-and-go flow pattern favored adhesion of ETX-treated erythrocytes to HUVECs. These findings suggest that altered RBCs interact with altered flow patterns potentially contributing to the microcirculatory injury observed in sepsis.

Red cell ICAM-4 is a novel ligand for platelet-activated alpha IIbbeta 3 integrin

ICAM-4 (LW blood group glycoprotein) is an erythroid-specific membrane component that belongs to the family of intercellular adhesion molecules and interacts in vitro with different members of the integrin family, suggesting a potential role in adhesion or cell interaction events, including hemostasis and thrombosis. To evaluate the capacity of ICAM-4 to interact with platelets, we have immobilized red blood cells (RBCs), platelets, and ICAM-Fc fusion proteins to a plastic surface and analyzed their interaction in cell adhesion assays with RBCs and platelets from normal individuals and patients, as well as with cell transfectants expressing the alpha(IIb)beta(3) integrin. The platelet fibrinogen receptor alpha(IIb)beta(3) (platelet GPIIb-IIIa) in a high affinity state following GRGDSP peptide activation was identified for the first time as the receptor for RBC ICAM-4. The specificity of the interaction was demonstrated by showing that: (i) activated platelets adhered less efficiently to immobilized ICAM-4-negative than to ICAM-4-positive RBCs, (ii) monoclonal antibodies specific for the beta(3)-chain alone and for a complex-specific epitope of the alpha(IIb)beta(3) integrin, and specific for ICAM-4 to a lesser extent, inhibited platelet adhesion, whereas monoclonal antibodies to GPIb, CD36, and CD47 did not, (iii) activated platelets from two unrelated type-I glanzmann's thrombasthenia patients did not bind to coated ICAM-4. Further support to RBC-platelet interaction was provided by showing that dithiothreitol-activated alpha(IIb)beta(3)-Chinese hamster ovary transfectants strongly adhere to coated ICAM-4-Fc protein but not to ICAM-1-Fc and was inhibitable by specific antibodies. Deletion of individual Ig domains of ICAM-4 and inhibition by synthetic peptides showed that the alpha(IIb)beta(3) integrin binding site encompassed the first and second Ig domains and that the G65-V74 sequence of domain D1 might play a role in this interaction. Although normal RBCs are considered passively entrapped in fibrin polymers during thrombus, these studies identify ICAM-4 as the first RBC protein ligand of platelets that may have relevant physiological significance.

WBC reduction reduces storage-associated RBC adhesion to human vascular endothelial cells under conditions of continuous flow in vitro

BACKGROUND

The effects of storage duration, WBC reduction, and irradiation on RBC adherence to vascular endothelia are unknown and are investigated under conditions of continuous flow.

STUDY DESIGN AND METHODS

Thirty-two RBC units were collected and divided into three groups, non-WBC-reduced (NWR), WBC-reduced (WR), and irradiated-WBC-reduced. Aliquots of RBCs were removed on Days 1, 15, and 28 of storage for analysis. The RBC suspensions were then perfused at a 1.5 percent Hct in a protein-poor medium under conditions of continuous flow over human umbilical vein endothelial cell monolayers. On each slide, 25 randomly chosen sites were videorecorded over 10 minutes, and the number of RBCs adherent to the endothelial cell monolayer was counted.

RESULTS

NWR RBCs stored for 28 days demonstrated a greater degree of adherence to endothelial cells compared to Days 1 and 15 (p < 0.03). The WR group had significantly fewer adherent RBCs than the NWR group on day 28 (p < 0.01). Irradiation had no effect on RBC adherence.

CONCLUSION

Prolonged storage of NWR RBCs increases RBC adherence to endothelial cells in vitro. WBC reduction before storage abrogates the effect of storage duration on increased adhesion. Studies to assess whether an in vivo effect occurs are required.