Erythrocytes enhance lymphocyte rolling and arrest in vivo

Molecular Pathways of Vulnerable Carotid Plaques at Risk of Ischemic Stroke: A Narrative Review

The concept of vulnerable carotid plaques is pivotal in understanding the pathophysiology of ischemic stroke secondary to large-artery atherosclerosis. In macroscopic evaluation, vulnerable plaques are characterized by one or more of the following features: microcalcification; neovascularization; lipid-rich necrotic cores (LRNCs); intraplaque hemorrhage (IPH); thin fibrous caps; plaque surface ulceration; huge dimensions, suggesting stenosis; and plaque rupture. Recognizing these macroscopic characteristics is crucial for estimating the risk of cerebrovascular events, also in the case of non-significant (less than 50%) stenosis. Inflammatory biomarkers, such as cytokines and adhesion molecules, lipid-related markers like oxidized low-density lipoprotein (LDL), and proteolytic enzymes capable of degrading extracellular matrix components are among the key molecules that are scrutinized for their associative roles in plaque instability. Through their quantification and evaluation, these biomarkers reveal intricate molecular cross-talk governing plaque inflammation, rupture potential, and thrombogenicity. The current evidence demonstrates that plaque vulnerability phenotypes are multiple and heterogeneous and are associated with many highly complex molecular pathways that determine the activation of an immune-mediated cascade that culminates in thromboinflammation. This narrative review provides a comprehensive analysis of the current knowledge on molecular biomarkers expressed by symptomatic carotid plaques. It explores the association of these biomarkers with the structural and compositional attributes that characterize vulnerable plaques.

Contrast-enhanced ultrasound evaluation of plaque vulnerability and the relationship between peripheral blood leukocytes

OBJECTIVE

To evaluate plaque vulnerability by carotid contrast-enhanced ultrasound (CEUS) and to analyze the correlation between plaque vulnerability and peripheral blood leukocyte classification.

MATERIALS AND METHODS

135 patients with carotid plaque were examined by contrast-enhanced ultrasound. Plaque vulnerability was assessed by semiquantitative visual classification. Baseline clinical data and peripheral leukocyte classification were collected. Ordered logistic regression was used to analyze the correlation between plaque neovascularization grade and peripheral leukocyte classification count.

RESULTS

There were significant differences in leukocyte, monocyte, neutrophil, mean platelet volume, lymphocyte, and neutrophil counts between different neovascular plaque grades and peripheral blood (P < 0.05). Correlation analysis showed that leukocyte, monocyte, and neutrophil counts were significantly positively correlated.

CONCLUSION

The increase in plaque neovascularization is associated with an increase in circulating leukocytes, monocytes, and neutrophils. Therefore, CEUS combined with peripheral blood leukocytes may serve as an early warning of plaque vulnerability and provide a theoretical basis for clinical treatment.

The role of coagulome in the tumor immune microenvironment

The rising incidence and persistent thrombosis in multiple cancers including those that are immunosuppressive highlight the need for understanding the tumor coagulome system and its role beyond hemostatic complications. Immunotherapy has shown significant benefits in solid organ tumors but has been disappointing in the treatment of hypercoagulable cancers, such as glioblastoma and pancreatic ductal adenocarcinomas. Thus, targeting thrombosis to prevent immunosuppression seems a clinically viable approach in cancer treatment. Hypercoagulable tumors often develop fibrin clots within the tumor microenvironment (TME) that dictates the biophysical characteristics of the tumor tissue. The application of systems biology and single-cell approaches highlight the potential role of coagulome or thrombocytosis in shaping the tumor immune microenvironment (TIME). In-depth knowledge of the tumor coagulome would provide unprecedented opportunities to better predict the hemostatic complications, explore how thrombotic stroma modulates tumor immunity, reexamine the significance of clinical biomarkers, and enable steering the stromal versus systemic immune response for boosting the effectiveness of immune checkpoint inhibitors in cancer treatment. We focus on the role of coagulation factors in priming a suppressive TIME and the huge potential of existing anticoagulant drugs in the clinical settings of cancer immunotherapy.

Anti-Inflammatory Effects of the 35kDa Hyaluronic Acid Fragment (B-HA/HA35)

Background

Hyaluronic acid (HA) and HA fragments interact with a variety of human body receptors and are involved in the regulation of various physiological functions and leukocyte trafficking in the body. Accordingly, the development of an injectable HA fragment with good tissue permeability, the identification of its indications, and molecular mechanisms are of great significance for its clinical application. The previous studies showed that the clinical effects of injectable 35kDa B-HA result from B-HA binding to multiple receptors in different cells, tissues, and organs. This study lays the foundation for further studies on the comprehensive clinical effects of injectable B-HA.

Methods

We elaborated on the production process, bioactivity assay, efficacy analyses, and safety evaluation of an injectable novel HA fragment with an average molecular weight of 35 kDa (35 kDa B-HA), produced by recombinant human hyaluronidase PH20 digestion.

Results

The results showed that 35 kDa B-HA induced human erythrocyte aggregation (rouleaux formation) and accelerated erythrocyte sedimentation rates through the CD44 receptor. B-HA application and injection treatment significantly promoted the removal of mononuclear cells from the site of inflammation and into the lymphatic circulation. At a low concentration, 35 kDa B-HA inhibited production of reactive oxygen species and tumor necrosis factor by neutrophils; at a higher concentration, 35 kDa B-HA promoted the migration of monocytes. Furthermore, 35 kDa B-HA significantly inhibited the migration of neutrophils with or without lipopolysaccharide treatment, suggesting that in local tissues, higher concentrations of 35 kDa B-HA have antiinflammatory effects. After 99mTc radiolabeled 35 kDa B-HA was intravenously injected into mice, it quickly entered into the spleen, liver, lungs, kidneys and other organs through the blood circulation.

Conclusion

This study demonstrated that the HA fragment B-HA has good tissue permeability and antiinflammatory effects, laying a theoretical foundation for further clinical studies.

IL-18 Promotes Erythrophagocytosis and Erythrocyte Degradation by M1 Macrophages in a Calcific Microenvironment

BACKGROUND

Calcific aortic-valve disease (CAVD) is the most common cause of aortic valve replacement in developed countries. Intraleaflet hemorrhage has been found to be positively correlated with the progression of CAVD. Although most research has focused on erythrocyte degradation products, which promote progression of CAVD, the process of erythrophagocytosis and erythrocyte degradation by macrophages in intraleaflet hemorrhage areas has remained unexplored.

METHODS

The erythrocyte degradation products of aortic valve specimens were detected by Perls' staining and quantified. The gene and protein expression levels of interleukin (IL)-18 in THP-1-polarized macrophages cultured in osteogenic medium were tested. We also quantified the iron and heme degraded by macrophages and analyzed the expression of ferroportin (FPN) and heme oxygenase-1 (HO-1) in the osteogenic medium. Furthermore, we tested the mRNA and protein levels of osteoblast markers in valve interstitial cells after co-culture with M1 macrophages treated with IL-18 and erythrocytes.

RESULTS

Our experiments demonstrated that IL-18 activates HO-1 and FPN to promote erythrophagocytosis and erythrocyte degradation by macrophages in a calcific microenvironment via p38 and Erk1/2. We also found that the calcific microenvironment promotes IL-18 mRNA and protein expression in THP-1-polarized macrophages.

CONCLUSIONS

In conclusion, IL-18 promotes M1 macrophage-mediated erythrophagocytosis and erythrocyte degradation by regulating the activation of HO-1 and FPN via p38 and Erk1/2 in a calcific microenvironment.

Integrin α4β1/VCAM-1 Interaction Evokes Dynamic Cell Aggregation Between Immune Cells and Human Lung Microvascular Endothelial Cells at Infectious Hemolysis

Bacterial and viral infection is a common cause of pneumonia, respiratory failure, and even acute respiratory distress syndrome. Increasing evidence indicates that red blood cells (RBCs) may contribute to immune response and inflammation. However, the precise molecular mechanisms that link RBC and hemolysis to the development and progression of inflammatory pathologies are not entirely understood. In this study, we used bacterial endotoxin, lipopolysaccharide (LPS), to mimic an infectious hemolysis and found that RBCs dynamically regulated cell aggregation between immune cells and human lung microvascular endothelial cells (HLMVEC). When RBCs were treated with LPS, integrin α4β1 was increased and was accompanied by cytokines and chemokines release (TNF-α, IL-1β, IL-6, IL-8, IFN-γ, CXCL12, CCL5, CCL7 and CCL4). Upon α4β1 elevation, RBCs not only facilitated mature monocyte derived dendritic cell (mo-DCs) adhesion but also promoted HLMVEC aggregation. Furthermore, co-culture of the supernatant of LPS pre-treated RBCs with mo-DCs could promote naïve CD4 T cell proliferation. Notably, the filtered culture from LPS-lysed RBCs further promoted mo-DCs migration in a concentration dependent manner. From a therapeutic perspective, cyclic peptide inhibitor of integrin α4β1 combined with methylprednisolone (α4β1/Methrol) remarkably blocked RBCs aggregation to mo-DCs, HLMVEC, or mo-DCs and HLMVEC mixture. Moreover, α4β1/Methrol dramatically reduced mo-DCs migration up-regulated glucocorticoid-induced leucine zipper in mo-DCs, and ultimately reversed immune cell dysfunction induced by hemolysis. Taken together, these results indicate that integrin α4β1 on RBCs could mediate cell-cell interaction for adaptive immunity through influencing cell adhesion, migration, and T cell proliferation.

Endothelial Barrier Function and Leukocyte Transmigration in Atherosclerosis

The vascular endothelium is a highly specialized barrier that controls passage of fluids and migration of cells from the lumen into the vessel wall. Endothelial cells assist leukocytes to extravasate and despite the variety in the specific mechanisms utilized by different leukocytes to cross different vascular beds, there is a general principle of capture, rolling, slow rolling, arrest, crawling, and ultimately diapedesis via a paracellular or transcellular route. In atherosclerosis, the barrier function of the endothelium is impaired leading to uncontrolled leukocyte extravasation and vascular leakage. This is also observed in the neovessels that grow into the atherosclerotic plaque leading to intraplaque hemorrhage and plaque destabilization. This review focuses on the vascular endothelial barrier function and the interaction between endothelial cells and leukocytes during transmigration. We will discuss the role of endothelial dysfunction, transendothelial migration of leukocytes and plaque angiogenesis in atherosclerosis.

An implantable blood clot-based immune niche for enhanced cancer vaccination

Cancer immunotherapy using cancer vaccines has shown great potential in the prevention and treatment of cancer. Here, we report an implantable autologous blood clot scaffold for enhanced cancer vaccination. It comprises a gel-like fibrin network formed by coagulation of blood to trap a large number of red blood cells. Upon implantation, the cross-linked RBCs in the blood clot can attract and recruit a great number of immune cells, leading to the formation of an "immune niche." Encapsulated with tumor-associated antigen and adjuvant, the blood clot vaccine (BCV) can induce a robust anticancer immune response. The BCV combined with immune checkpoint blockade effectively inhibits tumor growth in B16F10 and 4T1 tumor models. The proposed implantable blood clot cancer vaccine can be readily made by mixing the blood from patients with cancer with immunomodulating agents ex vivo, followed by reimplantation into the same patient for personalized cancer immunotherapy in future clinical translation.

Rapid improvement in carotid adventitial angiogenesis and plaque neovascularization after rosuvastatin therapy in statin treatment-naïve subjects

BACKGROUND

Statin therapy can improve plaque stability. However, the time course of effects of statin on adventitial angiogenesis and plaque neovascularization has not been studied.

OBJECTIVE

The objective of the study was to investigate whether statin therapy reduces plaque neovascularization, associated with adventitial angiogenesis, over 24 months as assessed by using carotid dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI).

METHODS

Forty-three lipid treatment-naïve subjects with asymptomatic carotid atherosclerosis received rosuvastatin (5-20 mg/d) to lower low-density lipoprotein cholesterol to <80 mg/dL for 24 months. Carotid DCE-MRI was performed at baseline, 3, 12 and 24 months. Vascularity (V_p = fractional plasma volume) and vascular permeability (K^trans = transfer constant) derived from kinetic modeling of DCE-MRI were measured in both adventitia and plaque.

RESULTS

Adventitia V_p and adventitia K^trans were significantly correlated with plaque V_p and plaque K^trans at baseline. Rosuvastatin significantly reduced both adventitial and plaque V_p significantly at 3 months from 0.121 ± 0.064 to 0.085 ± 0.049 (P = .008) and from 0.096 ± 0.052 to 0.067 ± 0.043 (P = .013). Adventitial and plaque V_p continued to decrease by 43% and 34% at 12 months and by 49% and 45% at 24 months. However, the continued reductions from 3 to 12 months and from 12 to 24 months were not statistically significant. Adventitial and plaque K^trans showed similar trends, but nonstatistically significant decreases during the 24 months of treatment.

CONCLUSIONS

Rosuvastatin therapy rapidly and significantly decreased adventitial and plaque neovascularization at 3 months followed by continued, but nonstatistically significant, decreases at 12 and 24 months.

Proliferating tumor cells mimick glucose metabolism of mature human erythrocytes

Mature human erythrocytes are dependent on anerobic glycolysis, i.e. catabolism (oxidation) of one glucose molecule to produce two ATP and two lactate molecules. Proliferating tumor cells mimick mature human erythrocytes to glycolytically generate two ATP molecules. They deliberately avoid or switch off their respiration, i.e. tricarboxylic acid (TCA) cycle and oxidative phosphorylation (OXPHOS) machinery and consequently dispense with the production of additional 36 ATP molecules from one glucose molecule. This phenomenon is named aerobic glycolysis or Warburg effect. The present review deals with the fate of a glucose molecule after entering a mature human erythrocyte or a proliferating tumor cell and describes why it is useful for a proliferating tumor cell to imitate a mature erythrocyte. Blood consisting of plasma and cellular components (99% of the cells are erythrocytes) may be regarded as a mobile organ, constantly exercising a direct interaction with other organs. Therefore, the use of drugs, which influences the biological activity of erythrocytes, has an immediate effect on the entire organism.

Abbreviations: TCA: tricarboxylic acid cycle; OXPHOS: oxidative phosphorylation; GSH: reduced state of glutathione; NFκB: Nuclear factor of kappa B; PKB (Akt): protein kinase B; NOS: nitric oxide synthase; IgG: immune globulin G; H₂S: hydrogen sulfide; slanDCs: Human 6-sulfo LacNAc-expressing dendritic cells; IL-8: interleukin-8; LPS: lipopolysaccharide; ROS: reactive oxygen species; PPP: pentose phosphate pathway; NADPH: nicotinamide adenine dinucleotide phosphate hydrogen; R5P: ribose-5-phophate; NAD: nicotinamide adenine dinucleotide; FAD: flavin adenine dinucleotide; O₂^●−: superoxide anion; G6P: glucose 6-phosphate; HbO₂: Oxyhemoglobin; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GAP: glyceraldehyde-3-phosphate; 1,3-BPG: 1,3-bis-phosphoglycerate; 2,3-BPG: 2,3-bisphosphoglycerte; PGAM1: phosphoglycerate mutase 1; 3-PG: 3-phosphoglycerate; 2-PG: 2-phosphoglycerate; MIPP1: Multiple inositol polyphosphate phosphatase; mTORC1: mammalian target of rapamycin complex 1; Ru5P: ribulose 5-phosphate; ox-PPP: oxidative branch of pentose phosphate pathway; PGK: phosphoglycerate kinase; IFN-γ: interferon-γ; LDH: lactate dehydrogenase; STAT3: signal transducer and activator of transcription 3; Rheb: Ras homolog enriched in Brain; H₂O₂: hydrogen peroxide; ROOH: lipid peroxide; SOD: superoxide dismutase; MRC: mitochondrial respiratory chain; MbFe²⁺-O₂: methmyoglobin; RNR: ribonucleotide reductase; PRPP: phosphoribosylpyrophosphate; PP_i: pyrophosphate; GSSG: oxidized state of glutathione; non-ox-PPP: non-oxidative branch of pentose phosphate pathway; RPI: ribose-5-phosphate isomerase; RPE: ribulose 5-phosphate 3-epimerase; X5P: xylulose 5-phosphate; TK: transketolase; TA: transaldolase; F6P: fructose-6-phosphate; AR2: aldose reductase 2; SD: sorbitol dehydrogenase; HK: hexokinase; MG: mehtylglyoxal; DHAP: dihydroxyacetone phosphate; TILs: tumor-infiltrating lymphocytes; MCTs: monocarboxylate transporters; pHi: intracellular pH; Hif-1α: hypoxia-induced factor 1; NHE1: sodium/H⁺ (Na⁺/H⁺) antiporter 1; V-ATPase: vacuolar-type proton ATPase; CAIX: carbonic anhydrase; CO₂: carbon dioxide; HCO₃⁻: bicarbonate; NBC: sodium/bicarbonate (Na⁺/HCO₃⁻) symporter; pHe: extracellular pH; GLUT-1: glucose transporter 1; PGK-1: phosphoglycerate kinase 1

Influence of Erythrocyte Membrane Stability in Atherosclerosis

PURPOSE OF REVIEW

The purpose of this study is to show how an excess of cholesterol in the erythrocyte membrane contributes stochastically to the progression of atherosclerosis, leading to damage in blood rheology and O₂ transport, deposition of cholesterol (from trapped erythrocytes) in an area of intraplaque hemorrhage, and local exacerbation of oxidative stress.

RECENT FINDINGS

Cholesterol contained in the membrane of erythrocytes trapped in an intraplaque hemorrhage contributes to the growth of the necrotic nucleus. There is even a relationship between the amount of cholesterol in the erythrocyte membrane and the severity of atherosclerosis. In addition, the volume variability among erythrocytes, measured by RDW, is predictive of a worsening of this disease. Erythrocytes contribute to the development of atherosclerosis in several ways, especially when trapped in intraplate hemorrhage. These erythrocytes are oxidized and phagocytosed by macrophages. The cholesterol present in the membrane of these erythrocytes subsequently contributes to the growth of the atheroma plaque. In addition, when they rupture, erythrocytes release hemoglobin, which leads to the generation of free radicals. Finally, increased RDW may predict the worsening of atherosclerosis, due to the effects of inflammation and oxidative stress on erythropoiesis and erythrocyte volume. A better understanding of erythrocyte participation in atherosclerosis may contribute to the improvement of the prevention and treatment strategies of this disease.

Plaque angiogenesis and intraplaque hemorrhage in atherosclerosis

Acute cardiovascular events, due to rupture or erosion of an atherosclerotic plaque, represent the major cause of morbidity and mortality in patients. Growing evidence suggests that plaque neovascularization is an important contributor to plaque growth and instability. The vessels' immaturity, with profound structural and functional abnormalities, leads to recurrent intraplaque hemorrhage. This review discusses new insights of atherosclerotic neovascularization, including the effects of leaky neovessels on intraplaque hemorrhage, both in experimental models and humans. Furthermore, modalities for in vivo imaging and therapeutic interventions to target plaque angiogenesis will be discussed.

Role of the endothelial surface layer in neutrophil recruitment

Neutrophil recruitment in most tissues is limited to postcapillary venules, where E- and P-selectins are inducibly expressed by venular endothelial cells. These molecules support neutrophil rolling via binding of PSGL-1 and other ligands on neutrophils. Selectins extend ≤ 38 nm above the endothelial plasma membrane, and PSGL-1 extends to 50 nm above the neutrophil plasma membrane. However, endothelial cells are covered with an ESL composed of glycosaminoglycans that is ≥ 500 nm thick and has measurable resistance against compression. The neutrophil surface is also covered with a surface layer. These surface layers would be expected to completely shield adhesion molecules; thus, neutrophils should not be able to roll and adhere. However, in the cremaster muscle and in many other models investigated using intravital microscopy, neutrophils clearly roll, and their rolling is easily and quickly induced. This conundrum was thought to be resolved by the observation that the induction of selectins is accompanied by ESL shedding; however, ESL shedding only partially reduces the ESL thickness (to 200 nm) and thus is insufficient to expose adhesion molecules. In addition to its antiadhesive functions, the ESL also presents neutrophil arrest-inducing chemokines. ESL heparan sulfate can also bind L-selectin expressed by the neutrophils, which contributes to rolling and arrest. We conclude that ESL has both proadhesive and antiadhesive functions. However, most previous studies considered either only the proadhesive or only the antiadhesive effects of the ESL. An integrated model for the role of the ESL in neutrophil rolling, arrest, and transmigration is needed.

Crosstalk between red blood cells and the immune system and its impact on atherosclerosis

Atherosclerosis is a chronic multifactorial disease of the arterial wall characterized by inflammation, oxidative stress, and immune system activation. Evidence exists on a pathogenic role of oxidized red blood cells (RBCs) accumulated in the lesion after intraplaque hemorrhage. This review reports current knowledge on the impact of oxidative stress in RBC modifications with the surface appearance of senescent signals characterized by reduced expression of CD47 and glycophorin A and higher externalization of phosphatidylserine. The review summarizes findings indicating that oxidized, senescent, or stored RBCs, due to surface antigen modification and release of prooxidant and proinflammatory molecules, exert an impaired modulatory activity on innate and adaptive immune cells and how this activity contributes to atherosclerotic disease. In particular RBCs from patients with atherosclerosis, unlike those from healthy subjects, fail to control lipopolysaccharide-induced DC maturation and T lymphocyte apoptosis. Stored RBCs, accompanied by shedding of extracellular vesicles, stimulate peripheral blood mononuclear cells to release proinflammatory cytokines, augment mitogen-driven T cell proliferation, and polarize macrophages toward the proinflammatory M1 activation pathway. Collectively, literature data suggest that the crosstalk between RBCs with immune cells represents a novel mechanism by which oxidative stress can contribute to atherosclerotic disease progression and may be exploited for therapeutic interventions.

Deformable cell-cell and cell-substrate interactions in semi-infinite domain

Leukocyte trafficking in the microvasculature during inflammatory response is known to involve multiple adhesion molecules and is referred to as the leukocyte adhesion cascade (LAC). Surface-bound selectins and their respective ligands are primarily responsible for tethering and rolling of leukocytes over inflamed endothelium. Numerical modeling of this response is challenging due to the nature of cell-cell interactions in Stokes flow (i.e., large domain of influence for each cell over its neighbors). Here, we discuss a novel simulation capable of modeling several steps of the LAC. The new model includes relevant contact and lubrication forces and extends a physics-based model for single particle rolling interactions developed by Hammer and Apte (1992), for multiparticle interactions by King and Hammer (2001a), and for deformable particles by Gee and King (2006). We initially demonstrate the model for cell-cell collisions occurring near a planar substrate, and for cell-substrate adhesive interactions. The adhesion studies provide a new perspective of the contribution of Hertzian contact mechanics toward variations in contact area at the cell-substrate interface. The results confirm that interfacial contact area will increase as a result of the contact formulation and that this mechanism may enhance cell rolling interactions for cells driven toward endothelium by cell-cell collisions. As a result of cell compliance, rolling velocity may decrease significantly, compared to non-compliant cells.

Forces on a wall-bound leukocyte in a small vessel due to red cells in the blood stream

As part of the inflammation response, white blood cells (leukocytes) are well known to bind nearly statically to the vessel walls, where they must resist the force exerted by the flowing blood. This force is particularly difficult to estimate due to the particulate character of blood, especially in small vessels where the red blood cells must substantially deform to pass an adhered leukocyte. An efficient simulation tool with realistically flexible red blood cells is used to estimate these forces. At these length scales, it is found that the red cells significantly augment the streamwise forces that must be resisted by the binding. However, interactions with the red cells are also found to cause an average wall-directed force, which can be anticipated to enhance binding. These forces increase significantly as hematocrit values approach 25% and decrease significantly as the leukocyte is made flatter on the wall. For a tube hematocrit of 25% and a spherical protrusion with a diameter three-quarters that of the vessel, the average forces are increased by ~40% and the local forces are more than double those estimated with an effective-viscosity-homogenized blood. Both the enhanced streamwise and wall-ward forces and their unsteady character are potentially important in regard to binding mechanisms.

Extracellular RNA promotes leukocyte recruitment in the vascular system by mobilising proinflammatory cytokines

Extracellular RNA (eRNA), released from cells under conditions of injury or vascular disease, acts as potent prothrombotic factor and promotes vascular hyperpermeability related to oedema formation in vivo. In this study, we aimed to investigate the mechanism by which eRNA triggers inflammatory processes, particularly associated with different steps of leukocyte recruitment. Using intravital microscopy of murine cremaster muscle venules, eRNA (but not DNA) significantly induced leukocyte adhesion and transmigration in vivo, which was comparable in its effects to the function of tumour-necrosis-factor-α (TNF-α). In vitro, eRNA promoted adhesion and transmigration of monocytic cells on and across endothelial cell monolayers. eRNA-induced monocyte adhesion in vitro was mediated by activation of the vascular endothelial growth factor (VEGF)/VEGF-receptor-2 system and was abolished by neutralising antibodies against intercellular adhesion molecule-1 or the β2-integrin Mac-1. Additionally, eRNA induced the release of TNF-α from monocytic cells in a time- and concentration-dependent manner, which involved activation of TNF-α-converting enzyme (TACE) as well as the nuclear factor κB signalling machinery. In vivo, inhibiton of TACE significantly reduced eRNA-induced leukocyte adhesion. Our findings present evidence that eRNA in connection with tissue/vascular damage provokes a potent inflammatory response by inducing leukocyte recruitment and by mobilising proinflammatory cytokines from monocytes.

Redox imbalance of red blood cells impacts T lymphocyte homeostasis: implication in carotid atherosclerosis

Oxidative stress and immune/inflammatory responses are key pathogenetic factors of atherosclerotic disease. In this contest, mechanisms that regulate survival and death of immune cells may be relevant. Previous studies have demonstrated that red blood cells (RBCs) are physiologically able to inhibit apoptosis and to promote proliferation of activated T lymphocytes from healthy subjects. The aim of the present study was to evaluate whether RBCs from patients with carotid atherosclerosis maintain their property to modulate T cell homeostasis. Peripheral blood lymphocytes (PBLs) obtained from healthy subjects were activated in vitro by phytohemagglutinin in the presence/absence of RBCs from patients with carotid atherosclerosis or of in vitro oxidised RBCs from healthy subjects. Levels of reactive oxygen species (ROS) and aging markers of RBCs as well as susceptibility to apoptosis of PBLs were evaluated by flow cytometry. PBL proliferation was evaluated by 3H-methyl-thymidine incorporation assay whereas secretion of cytokines, analysed in view of their key role in T cell function, was assessed by ELISA. Levels of ROS and phosphatidyl-serine externalisation, a sign of RBC aging, resulted significantly higher in RBCs from patients than in those from healthy subjects, whereas surface glycophorin A expression and reduced glutathione content did the opposite. Unlike RBCs obtained from healthy subjects, RBCs from patients and in vitro oxidised RBCs did not protect activated T lymphocytes from apoptosis. Hence, RBCs from patients with carotid atherosclerosis, probably due to their oxidative imbalance, impact T cell integrity and function. Our results suggest a new regulatory role for RBCs in atherosclerosis.

Biomimetic postcapillary expansions for enhancing rare blood cell separation on a microfluidic chip

Blood cells naturally auto-segregate in postcapillary venules, with the erythrocytes (red blood cells, RBCs) aggregating near the axis of flow and the nucleated cells (NCs)--which include leukocytes, progenitor cells and, in cancer patients, circulating tumor cells--marginating toward the vessel wall. We have used this principle to design a microfluidic device that extracts nucleated cells (NCs) from whole blood. Fabricated using polydimethylsiloxane (PDMS) soft lithography, the biomimetic cell extraction device consists of rectangular microchannels that are 20-400 μm wide, 11 μm deep and up to 2 cm long. The key design feature is the use of repeated expansions/contractions of triangular geometry mimicking postcapillary venules, which enhance margination and optimize the extraction. The device operates on unprocessed whole blood and is able to extract 94 ± 4.5% of NCs with 45.75 ± 2.5-fold enrichment in concentration at a rate of 5 nl s(-1). The device eliminates the need to preprocess blood via centrifugation or RBC lysis, and is ready to be implemented as the initial stage of lab-on-a-chip devices that require enriched nucleated cells. The potential downstream applications are numerous, encompassing all preclinical and clinical assays that operate on enriched NC populations and include on-chip flow cytometry (A. Y. Fu et al., Anal. Chem., 2002, 74, 2451-2457; A. Y. Fu et al., Nat. Biotechnol., 1999, 17, 1109-1111), genetic analyses (M. M. Wang et al., Nat. Biotechnol., 2005, 23, 83-87; L. C. Waters et al., Anal. Chem., 1998, 70, 5172-5176) and circulating tumor cell extraction (S. Nagrath et al., Nature, 2007, 450, 1235-1241; S. L. Stott et al., Proc. Natl. Acad. Sci. U. S. A., 2010, 18392-18397; H. K. Lin et al., Clin. Cancer Res., 2010, 16, 5011-5018).

Red blood cells carry out T cell growth and survival bioactivities that are sensitive to cyclosporine A

Red blood cells (RBC) have emerged as a novel regulatory cell type endowed with bioactivities toward activated human T cells. Herein we show that the RBC bioactivities act on intracellular pathways initiated by T cell receptor (TCR)-dependent and -independent stimuli,including IL-2, IL-15, and the mixture of phorbol dibutyrate and ionomycin. The RBC bioactivities preserve the antioxidant status and are capable of rescuing activated T cells from cell death induced by serum deprivation. They are not mediated by glycosylphosphatidylinositol-linked receptors or sialic acids, and kinetic studies revealed that they hasten the entrance into the cell cycle. By using cyclosporine A (CsA) and rapamycin (Rapa) we show that the RBC bioactivities are calcineurin-dependent. Thus, treatment of T cells with CsA, but not Rapa, impaired RBC bioactivities, and preincubation of RBC with CsA completely abolished their bioactivities. We have demonstrated that RBC carry out bioactivities that are sensitive to CsA.

Biological effects of dynamic shear stress in cardiovascular pathologies and devices

Altered and highly dynamic shear stress conditions have been implicated in endothelial dysfunction leading to cardiovascular disease, and in thromboembolic complications in prosthetic cardiovascular devices. In addition to vascular damage, the pathological flow patterns characterizing cardiovascular pathologies and blood flow in prosthetic devices induce shear activation and damage to blood constituents. Investigation of the specific and accentuated effects of such flow-induced perturbations on individual cell-types in vitro is critical for the optimization of device design, whereby specific design modifications can be made to minimize such perturbations. Such effects are also critical in understanding the development of cardiovascular disease. This review addresses limitations to replicate such dynamic flow conditions in vitro and also introduces the idea of modified in vitro devices, one of which is developed in the authors' laboratory, with dynamic capabilities to investigate the aforementioned effects in greater detail.

Angiogenesis and endothelial cell repair in renal disease and allograft rejection

This review discusses the concept that the turnover and replacement of endothelial cells is a major mechanism in the maintenance of vascular integrity within the kidney. CD133+CD34+KDR+ endothelial cell progenitor cells emigrate from the bone marrow and differentiate into CD34+KDR+ expressing cells, which are present in high numbers within the circulation. These progenitor cells are available for recruitment into normal or inflamed tissues to facilitate endothelial cell repair. In several forms of renal disease, proinflammatory insults mediate oxidative stress, senescence, and sloughing of endothelial cells. A lack of growth factors or an inefficient recruitment of endothelial cell progenitors results in hypoxic tissue injury and accelerates the process of chronic renal failure. Augmentation of vascular repair by the provision of growth factors such as vascular endothelial growth factor or by the transfer of progenitor cells directly into the kidney can be protective and prevent ongoing interstitial damage. In allografts, persistent injury results in excessive turnover of graft vascular endothelial cells. Moreover, chronic damage elicits a response that is associated with the recruitment of both leukocytes and endothelial cell progenitors, facilitating an overlapping process of inflammation and angiogenesis. Because the angiogenesis reaction itself is proinflammatory, this process becomes self-sustaining. Collectively, these data indicate that angiogenesis and endothelial cell turnover are important in renal inflammatory processes and allograft rejection. Manipulation of the response may have therapeutic implications to protect against injury and chronic disease processes.

Monocyte recruitment to endothelial cells in response to oscillatory shear stress

Leukocyte recruitment to endothelial cells is a critical event in inflammatory responses. The spatial, temporal gradients of shear stress, topology, and outcome of cellular interactions that underlie these responses have so far been inferred from static imaging of tissue sections or studies of statically cultured cells. In this report, we developed micro-electromechanical systems (MEMS) sensors, comparable to a single endothelial cell (EC) in size, to link real-time shear stress with monocyte/EC binding kinetics in a complex flow environment, simulating the moving and unsteady separation point at the arterial bifurcation with high spatial and temporal resolution. In response to oscillatory shear stress (tau) at +/- 2.6 dyn/cm2 at a time-averaged shear stress (tau(ave))=0 and 0.5 Hz, individual monocytes displayed unique to-and-fro trajectories undergoing rolling, binding, and dissociation with other monocyte, followed by solid adhesion on EC. Our study quantified individual monocyte/EC binding kinetics in terms of displacement and velocity profiles. Oscillatory flow induces up-regulation of adhesion molecules and cytokines to mediate monocyte/EC interactions over a dynamic range of shear stress +/- 2.6 dyn/cm2 (P=0.50, n=10).

Red blood cells initiate leukocyte rolling in postcapillary expansions: a lattice Boltzmann analysis

Leukocyte rolling on the vascular endothelium requires initial contact between leukocytes circulating in the blood and the vessel wall. Although specific adhesion mechanisms are involved in leukocyte-endothelium interactions, adhesion patterns in vivo suggest other rheological mechanisms also play a role. Previous studies have proposed that the abundance of leukocyte rolling in postcapillary venules is due to interactions between red blood cells (RBCs) and leukocytes as they enter postcapillary expansions, but the details of the fluid dynamics have not been elucidated. We have analyzed the interactions of red and white blood cells as they flow from a capillary into a postcapillary venule using a lattice Boltzmann approach. This technique provides the complete solution of the flow field and quantification of the particle-particle forces in a relevant geometry. Our results show that capillary-postcapillary venule diameter ratio, RBC configuration, and RBC shape are critical determinants of the initiation of cell rolling in postcapillary venules. The model predicts that an optimal configuration of the trailing red blood cells is required to drive the white blood cell to the wall.

Analyzing the migration of labeled T cells in vivo: an essential approach with challenging features

T cells are involved in the pathogenesis of many diseases. To exert a pathological effect, T cells enter the tissues. We show that the determination of their entry site requires isolation of the respective T cell population, injection into genetically un-manipulated animals, and identification of the cells in vivo at various time points after injection. We indicate variables influencing in vivo migration experiments artificially, and outline how resulting problems can be either avoided or taken into account. Reviewing experiments performed according to the outlined criteria reveals two types of migration patterns for T cell subsets in vivo: 1). Naïve and memory T cells enter lymphoid and non-lymphoid organs in comparable numbers, but selectively accumulate in lymphoid tissues over time, 2). Effector T cells, too, enter lymphoid and non-lymphoid organs in comparable numbers. However, most of them die within 24 hours. Depending on the presence of cytokines, chemokines and extracellular matrix compounds they are able to survive, thereby preferentially accumulating in their target tissues. This information might help to understand the role of migration in the pathogenesis of T cell mediated diseases.

Dynamic deformation of migratory efferent lymph-derived cells "trapped" in the inflammatory microcirculation

The cellular immune response depends on the delivery of lymphocytes from the lymph node to the peripheral site of antigenic challenge. During their passage through the inflammatory microcirculaton, the migratory cells can become transiently immobilized or "trapped" in small caliber vessels. In this report, we used intravital microscopy and temporal area mapping to define the dynamic deformation of efferent lymph-derived mononuclear cells trapped in the systemic inflammatory microcirculation. Mononuclear cells obtained from the efferent lymph draining the oxazolone-stimulated microcirculation were labeled with fluorescent dye and reinjected into the feeding arterial circulation. Intravital video microscopy observed thousands of cells passing through the microcirculation; 35 cells were "trapped" in the oxazolone-stimulated microcirculation. Temporal area maps of the trapped cells demonstrated dramatic slowing and deformation. The cells were trapped in the microcirculation for a median of 8.90 sec (range 5-17 sec) prior to returning to the flow stream. During this period, the cells showed sustained movement associated with both antegrade locomotion (mean cell velocity = 7.92 microm/sec; range 1.16-14.23 microm/sec) and dynamic elongation (median cell length = 73.8 microm; range 58-144 microm). In contrast, efferent lymph-derived cells passing unimpeded through the microcirculation demonstrated rapid velocity (median velocity = 216 microm/sec) and spherical geometry (median diameter = 14.6 microm). Further, the membrane surface area of the "trapped" cells, calculated based on digital image morphometry and corrosion cast scanning electron microscopy, suggested that the fractional excess membrane of the cells in the efferent lymph was significantly greater than previous estimates of membrane excess. These data indicate that transient immobilization of efferent lymph-derived mononuclear cells in the systemic inflammatory microcirculation is rare. When "trapping" does occur, the shape changes and sustained cell movement facilitated by excess cell membrane may contribute to the return of the "trapped cells" into the flow stream.

Red blood cells augment leukocyte rolling in a virtual blood vessel

Leukocyte rolling and arrest on the vascular endothelium is a central event in normal and pathological immune responses. However, rigorous estimation of the fluid and surface forces involved in leukocyte-endothelial interactions has been difficult due to the particulate, non-Newtonian nature of blood. Here we present a Lattice-Boltzmann approach to quantify forces exerted on rolling leukocytes by red blood cells in a "virtual blood vessel." We report that the normal force imparted by erythrocytes is sufficient to increase leukocyte binding and that increases in tangential force and torque can promote rolling of previously adherent leukocytes. By simulating changes in hematocrit we show that a close "envelopment" of the leukocyte by the red blood cells is necessary to produce significant changes in the forces. This novel approach can be applied to a large number of biological and industrial problems involving the complex flow of particulate suspensions.

Targeting microparticles to select tissue via radiation-induced upregulation of endothelial cell adhesion molecules

PURPOSE

Certain endothelial cell adhesion molecules are up regulated in tissue that has been irradiated for therapeutic purposes. This up-regulation of adhesion molecules provides a potential avenue for targeting drugs to select tissues.

METHODS

Microspheres were coated with a mAb to ICAM-1 and the level of adhesion of the anti-ICAM-1 microspheres to irradiated tissue in vitro and in vivo was quantified.

RESULTS

Under in vitro flow conditions, the number of adherent microspheres on irradiated HUVEC was 4.8 +/- 0.9 times that of control; the adhesion of anti-ICAM-1 microspheres on irradiated HUVEC could be enhanced by more than 170% in the presence of RBC (20% hematocrit) in the medium. In vivo in a rat cranial window model, the number of adherent anti-ICAM-1 microspheres in locally irradiated cerebral tissue was 8 and 13 times that of IgG microspheres at 24 h and 48 h post-irradiation, respectively and returned to baseline 7 days post-irradiation. In locally irradiated animals, the number of adhering microspheres in unirradiated tissue remained at the basal level.

CONCLUSIONS

Radiation-induced up-regulation of endothelial cell adhesion molecules may be exploited to target drugs and/or genes to select segments of the endothelium.

Dissecting tumour pathophysiology using intravital microscopy

For a systemically administered therapeutic agent to reach neoplastic cells, it must enter the blood circulation, cross the vessel wall, move through the extracellular matrix and avoid getting cleared by the lymphatics. In tumours, each of these barriers is abnormal, changes with space and time, and depends on host-tumour interactions. Intravital microscopy has provided unprecedented molecular, cellular, anatomical and functional insights into these barriers and has revealed new approaches to improved detection and treatment.

Focal topographic changes in inflammatory microcirculation associated with lymphocyte slowing and transmigration

Microcirculation is the primary mechanism for delivering lymphocytes to inflammatory tissues. Blood flow within microvessels ensures a supply of lymphocytes at the blood-endothelial interface. Whether the structure of the inflammatory microcirculation facilitates lymphocyte transmigration is less clear. To illuminate the microcirculatory changes associated with lymphocyte transmigration, we used intravital videomicroscopy to examine the dermal microcirculation after application of the epicutaneous antigen oxazolone. Intravascular injection of fluorescein-labeled dextran demonstrated focal topographic changes in the microcirculation. These focal changes had the appearance of loops or hairpin turns in the oxazolone-stimulated skin. Changes were maximal at 96 h and coincided with peak lymphocyte recruitment. To determine whether these changes were associated with lymphocyte transmigration, lymphocytes obtained from efferent lymph of draining lymph nodes at 96 h were fluorescently labeled and reinjected into inflammatory microcirculation. Epifuorescence intravital video microscopy demonstrated focal areas were associated with lymphocyte slowing and occasional transmigration. In contrast, focal loops and lymphocyte slowing were rarely observed in the contralateral control microcirculation. Results suggest that structural adaptations in inflammatory microcirculation represented by focal topographic changes may contribute to regulation of tissue entry by recirculating lymphocytes.

Multiparticle adhesive dynamics. Interactions between stably rolling cells

A novel numerical simulation of adhesive particles (cells) reversibly interacting with an adhesive surface under flow is presented. Particle--particle and particle--wall hydrodynamic interactions in low Reynolds number Couette flow are calculated using a boundary element method that solves an integral representation of the Stokes equation. Molecular bonds between surfaces are modeled as linear springs and stochastically formed and broken according to postulated descriptions of force-dependent kinetics. The resulting simulation, Multiparticle Adhesive Dynamics, is applied to the problem of selectin-mediated rolling of hard spheres coated with leukocyte adhesion molecules (cell-free system). Simulation results are compared to flow chamber experiments performed with carbohydrate-coated spherical beads rolling on P-selectin. Good agreement is found between theory and experiment, with the main observation being a decrease in rolling velocity with increasing concentration of rolling cells or increasing proximity between rolling cells. Pause times are found to increase and deviation motion is found to decrease as pairs of rolling cells become closer together or align with the flow.

Delivery of molecular medicine to solid tumors: lessons from in vivo imaging of gene expression and function

Extraordinary advances in molecular medicine and biotechnology have led to the development of a vast number of anti-cancer therapeutic agents. To reach cancer cells in a tumor, a blood-borne therapeutic molecule, particle or cell must make its way into the blood vessels of the tumor and across the vessel wall into the interstitium and finally migrate through the interstitium. Unfortunately, tumors often develop in ways that hinder each of these steps. Our research goals are to analyze each of these steps experimentally and theoretically and then integrate the resulting information in a unified theoretical framework. This paradigm of analysis and synthesis has allowed us to obtain a better understanding of microcirculatory barriers in solid tumors and to develop novel strategies to exploit and/or to overcome these barriers for improved cancer detection and treatment.

Severe impairment of leukocyte rolling in venules of core 2 glucosaminyltransferase-deficient mice

Leukocyte capture and rolling are mediated by selectins expressed on leukocytes (L-selectin) and the vascular endothelium (P- and E-selectin). To investigate the role of core 2 beta1-6-N-glucosaminyltransferase (C2GlcNAcT-I) for synthesis of functional selectin ligands in vivo, leukocyte rolling flux and velocity were studied in venules of untreated and tumor necrosis factor-alpha (TNFalpha)-pretreated autoperfused cremaster muscles of C2GlcNAcT-I-deficient (core 2(-/-)) and littermate control mice. In untreated core 2(-/-) mice, leukocyte rolling was dramatically reduced with markedly increased rolling velocities (81 +/- 4 microm/s vs 44 +/- 3 microm/s). The reduced rolling in core 2(-/-) mice was due mainly to severely impaired binding of P-selectin to P-selectin glycoprotein ligand-1 (PSGL-1). Some rolling remained after blocking PSGL-1 in controls but not in core 2(-/-) mice. In TNFalpha-pretreated mice, rolling was markedly reduced in core 2(-/-) mice owing to impaired P-selectin- and E-selectin-mediated rolling. Rolling velocities in core 2(-/-) mice treated with an E-selectin-blocking monoclonal antibody (59 +/- 4 microm/s) were significantly higher than in controls (14 +/- 1 microm/s), which provides further evidence for the severe impairment in P-selectin-mediated rolling. In conclusion, P-selectin ligands including PSGL-1 are largely C2GlcNAcT-I dependent. In addition, E-selectin-mediated rolling in vivo is partially dependent on the targeted C2GlcNAcT-I. (Blood. 2001;97:3812-3819)

Red blood cells inhibit activation-induced cell death and oxidative stress in human peripheral blood T lymphocytes

Red blood cells (RBCs) are known to perform one prominent function: to carry and deliver oxygen to the tissues. Earlier studies, however, suggested a role for RBCs in potentiating T-cell proliferation in vitro. Here it is shown that the presence of RBCs in cultures of stimulated human peripheral blood lymphocytes strengthens T-cell proliferation and survival. Analysis of phosphatidylserine externalization and DNA fragmentation showed that RBCs inhibit T-cell apoptosis. This inhibition correlated with a reduction in CD71 but not CD95 expression. RBCs enhanced T-cell proliferation and survival upon activation with phytohemagglutinin and with OKT3 antibodies. Studies aimed at characterizing the cellular and molecular basis of the protection afforded to T cells by RBCs showed that (1) optimal protection required intact RBCs and red cell/T-cell contact but not monocytes; (2) RBCs markedly reduced the level of intracellular reactive oxygen species; and (3) RBCs inhibited the formation of protein-bound acrolein, a peroxidation adduct in biologic systems. Overall, these data indicate that human RBCs protect T cells from activation-induced cell death, at least in part by reducing the pro-oxidant state, and suggest a role for RBCs as conceivable modulators of T-cell homeostasis.