Selectins

Comprehensive analysis of L-PRF exudate components and their impact on whole blood platelets

OBJECTIVE

This study assessed the cellular composition and effects of leukocyte-platelet-rich fibrin (L-PRF) exudate on whole blood platelets from healthy volunteers. Key objectives included evaluating leukocyte subpopulations, platelet activation markers, platelet-leukocyte interactions and quantifying inflammatory cytokines within the L-PRF exudate.

MATERIALS AND METHODS

L-PRF was obtained from 20 healthy donors. Flow cytometry methodologies were used to assess intracellular calcium kinetics and activated GPIIbIIIa, and P-selectin expression. Leukocyte subpopulations and platelet-leukocyte interactions were characterized using monoclonal antibodies. Inflammatory cytokines (IL-8, IL-1β, IL-6, IL-10, TNF, IL-12p70) within L-PRF exudate were quantified using a cytometric bead array.

RESULTS

The expression of activated GPIIbIIIa, and P-selectin exhibited a significant increase (p < 0.001) when L-PRF exudate was added to platelets of whole blood. Regarding intracellular Ca2+ mobilization, the L-PRF exudate elicited significant responses (p < 0.001). L-PRF exudate contained different leukocytes populations, being TCD4 + the most representative of T cells. It was possible to stablish a profile of cytokines produced by the L-PRF exudate, with human IL-8 cytokine exhibiting the highest average (16.90 pg/mL).

CONCLUSIONS

Despite the study limitations, the research yielded important insights: 1- L-PRF exudate can stimulate platelet activation, essential in healing, tissue inflammation and remodeling. 2-The presence of leukocyte subpopulations within L-PRF exudate reflexes its complexity and potential to enhance immune responses. 3-The analysis of inflammatory cytokines within L-PRF exudate revealed its immunomodulatory potential. These findings are valuable evidences for understanding the potential role of L-PRF exudate in regenerative dentistry and medicine, offering innovative therapeutic strategies.

CLINICAL RELEVANCE

This research highlights crucial aspects that could significantly influence the clinical use of L-PRF exudate in the oral cavity. The findings support the application of L-PRF exudate in both surgical and regenerative dentistry, facilitating the development of innovative therapeutic strategies to enhance patient outcomes.

Crizanlizumab in sickle cell disease

Vaso-occlusion in sickle cell disease (SCD) leads to a myriad of manifestations driving morbidity and mortality in patients with SCD. Increased leucocyte adhesion and P-selectin expression on platelets and endothelial cells is an inciting event that leads to obstruction of microcirculation by adhesion with rigid sickled red blood cells. Crizanlizumab is a first-in-class monoclonal antibody that inhibits P-selectin and has been shown to decrease the frequency of vaso-occlusive pain crises in patients with SCD in clinical trials. The role of crizanlizumab in other manifestations of SCD still needs further investigation.

Engineering the Sialome

The surface of every eukaryotic cell is coated in a dense layer of structurally diverse glycans that together comprise the glycocalyx, a key interface between intracellular biochemistry and the external environment. Many of the glycans within the glycocalyx terminate in anionic monosaccharides belonging to the sialic acid family. Advances in our understanding of the biological processes mediated by sialic acids at the interfaces between cells have catalyzed interest in metabolic, enzymatic, and chemical strategies to edit the total complement of cellular sialic acids-the sialome. Here, we review strategies for altering the composition of the sialome with particular focus on glycan structures and state-of-the-art tools.

E-selectin negatively regulates polymorphonuclear neutrophil transmigration through altered endothelial junction integrity

Transendothelial migration (TEM) of neutrophils under blood flow is critical in the inflammatory cascade. However, the role of endothelial plasticity in this process is not fully understood. Therefore, we used an in vitro model to test the dynamics of human polymorphonuclear neutrophil (PMN) TEM across lipopolysaccharide-treated human umbilical vein endothelial cell (HUVEC) monolayers. Interestingly, shRNA-E-selectin knockdown in HUVECs destabilized endothelial junctional integrity by reducing actin branching and increasing stress fiber at cell-cell junctions. This process is accomplished by downregulating the activation of cortactin and Arp2/3, which in turn alters the adhesive function of VE-cadherin, enhancing PMN transmigration. Meanwhile, redundant P-selectins possess overlapping functions in E-selectin-mediated neutrophil adhesion, and transmigration. These results demonstrate, to our knowledge, for the first time, that E-selectins negatively regulate neutrophil transmigration through alterations in endothelial plasticity. Furthermore, it improves our understanding of the mechanisms underlying actin remodeling, and junctional integrity, in endothelial cells mediating leukocyte TEM.

Rational Design of Novel Glycomimetic Peptides for E-Selectin Targeting

E-selectin is a cell-adhesion receptor with specific recognition capacity toward sialo-fucosylated Lewis carbohydrates present in leukocytes and tumor cells. E-selectin interactions mediate the progress of inflammatory processes and tumor metastasis, which aroused the interest in using this protein as a biomolecular target to design glycomimetic inhibitors for active targeting or therapeutic purposes. In this work, we report the rational discovery of two novel glycomimetic peptides targeting E-selectin based on mutations of the reference selectin-binding peptide IELLQAR. Sixteen single or double mutants at Ile1, Leu3, Leu4, and Arg7 residues were evaluated as potential candidates for E-selectin targeting using 50 ns molecular dynamics (MD) simulations. Nine peptides showing a stable association with the functional pocket were modified by adding a cysteine residue to the N-terminus to confer versatility for further chemical conjugation. Subsequent 50 ns MD simulations resulted in five cysteine-modified peptides with retained or improved E-selectin binding potential. Then, 300 ns accelerated MD (aMD) simulations were used to examine the binding properties of the best five cysteine-modified peptides. CIEELQAR and CIELFQAR exhibit the most selective association with the functional pocket of E-selectin, as revealed by potential of mean force profiles. Microscale thermophoresis experiments confirmed the E-selectin binding capacity of the selected peptides with K_D values in the low micromolar range (CIEELQAR K_D = 35.0 ± 1.4 μM; CIELFQAR K_D = 16.4 ± 0.7 μM), which are 25-fold lower than the reported value for the native ligand sLe^x (K_D = 878 μM). Our findings support the potential of CIEELQAR and CIELFQAR as novel E-selectin-targeting peptides with high recognition capacity and versatility for chemical conjugation, which are critical for enabling future applications in active targeting.

P-Selectin Blockade in the Treatment of Painful Vaso-Occlusive Crises in Sickle Cell Disease: A Spotlight on Crizanlizumab

Microvascular vaso-occlusion driven pain crisis is the hallmark of sickle cell disease with profound morbidity and increased mortality. Selectins, most notably P-selectins have an integral role in this phenomenon. P-selection was first identified in 1989. In 2019, after 3 decades of basic, translational, and clinical work with this pathway, the US Food and Drug Administration approved a P-selectin antibody, crizanlizumab to reduce frequency of pain crisis in patients more than 16 years with sickle cell disease. We review the fundamentals of P-selectin pathobiology, P-selectin blocking agents, clinical data with the use of crizanlizumab and prospects of this novel class of drugs in the context of other treatments for painful vaso-occlusive episodes.

Immunoglobulin G in Platelet-Derived Wound Healing Factors

We intended to reformulate an existing platelet-derived wound healing formula to target each phase of the healing wound with the appropriate phase-specific molecules. A decreased perfusion of the skin, often associated with conditions such as thalassemia, sickle cell disease, diabetes mellitus, and chronic vascular disease, is the most common etiology of cutaneous ulcers and chronic wounds. We had previously shown that a PDWHF topically applied to a chronic nonhealing ulcer of a β-thalassemia homozygote stimulated and accelerated closure of the wound. The PDWHF was prepared from a pooled platelet concentrate of a matching blood group, consisting of a combination of platelet α-granule-derived factors. Processing of the apheresis-pooled platelets yielded various amounts of proteins (3.36 g/mL ± 0.25 (SD) (N = 10)) by the better lysis buffer method. Immunoglobulin G was found to be the most abundant α-granule-secreted protein. Equally broad quantities of the IgG (10.76 ± 12.66% (SD) (N = 10)) and IgG/albumin ratios (0.6 ± 0.4 (SD) (N = 10)) were quantified. We have developed a method using a reformulated lysis buffer followed by size exclusion chromatography and affinity chromatography to extract, identify, quantify, and purify IgG from activated platelets. IgG purification was confirmed by Western blot and flow cytometry. It was thought unlikely that the platelet IgG could be accounted for by adsorption of plasma protein, though the variable quantities could account for diversity in wound healing rates. The IgG could protect the wound even from subclinical infections and functionally advance healing. It may be useful in the management of skin ulcers in the early phase of wound healing.

Impact of real-time shedding on binding kinetics of membrane-remaining L-selectin to PSGL-1

L-selectin shedding induced by various cytokines is crucial in activating neutrophils (PMNs) in inflammatory cascade. While the real-time shedding in vivo lasts ~10 min after PMN activation, the impact of time-dependent shedding on binding kinetics of membrane-remaining L-selectins to its ligands is poorly understood at transient or steady state. Here, we developed an in vitro L-selectin shedding dynamics approach, together with competitive assays of cell adhesion, and proposed a theoretical model for quantifying the impact of real-time shedding on the binding kinetics of membrane-remaining L-selectins to P-selectin glycoprotein ligand-1 (PSGL-1). Our data indicated that the extent of L-selectin shedding on PMA activation is higher, but the terminating time is longer for Jurkat cells than those for human PMNs. Meanwhile, fMLF or IL-8 stimulation yields the longer terminating time than that on PMA stimulation but results in a similar shedding extent for PMNs. L-selectin shedding reduces L-selectin-PSGL-1-mediated cell adhesion in three ways: decreasing membrane-anchored L-selectins, increasing soluble L-selectins competitively binding to ligands, and presenting conformational alteration of membrane-remaining L-selectins themselves. Compared with those on intact cells, the binding affinities of membrane-remaining L-selectin-PSGL-1 pairs were all enhanced at initial and lowered at the late shedding phase for both PMN and Jurkat cells even with varied transition time points. The rolling velocities of both PMNs and Jurkat cells were increased following mechanically or biochemically induced shedding of L-selectin under shear flow. These findings help to further our understanding of the function of time-dependent L-selectin shedding during the inflammation cascade.

Standardization and reference ranges for whole blood platelet function measurements using a flow cytometric platelet activation test

Introduction

Platelet function testing with flow cytometry has additional value to existing platelet function testing for diagnosing bleeding disorders, monitoring anti-platelet therapy, transfusion medicine and prediction of thrombosis. The major challenge is to use this technique as a diagnostic test. The aim of this study is to standardize preparation, optimization and validation of the test kit and to determine reference values in a population of 129 healthy individuals.

Methods

Platelet function tests with 3 agonists and antibodies against P-selectin, activated αIIbβ3 and glycoprotein Ib (GPIb), were prepared and stored at -20°C until used. Diluted whole blood was added and platelet activation was quantified by the density of activation markers, using flow cytometry. Anti-mouse Ig κ particles were included to validate stability of the test and to standardize results. Reference intervals were determined.

Results

Blood stored at room temperature (RT) for up to 4h after blood donation and preheated/tested at 37°C resulted in stable results (%CV<10%), in contrast to measuring at RT. The intra-assay %CV was <5%. Incubation of anti-mouse Ig κ particles with antibodies stored for up to 12 months proved to give a stable fluorescence. The inter-individual variation measured in the 129 individuals varied between 23% and 37% for P-selectin expression and αIIbβ3 activation, respectively.

Conclusions

The current study contributes to the translation of flow cytometry based platelet function testing from a scientific tool to a diagnostic test. Platelet function measurements, using prepared and stored platelet activation kits, are reproducible if executed at 37°C. The reference ranges can be validated in clinical laboratories and ongoing studies are investigating if reduced platelet reactivity in patients with bleeding complications can be detected.

Preventive Effect of α-Tocopherol and Glycyrrhizin against Platelet-Neutrophil Complex Formation Induced by Hemodialysis Membranes

Background

The intradialytic activation of leukocytes is a major cause of hemodialysis (HD)-associated complications. Contact between blood and HD membranes frequently induces the formation of microaggregates composed of activated platelets and leukocytes, causing leukocyte activation that includes the generation of reactive oxygen species (ROS). This complex formation is mediated primarily by the interaction between P-selectin on activated platelets and its counter-ligands on leukocytes.

Objective

We examined the preventive effects of α-tocopherol and glycyrrhizin in vitro against platelet-neutrophil microaggregate formation and neutrophil ROS production induced by HD membranes.

Methods and Results

Microaggregate formation induced by the incubation of heparinized whole blood with polysulfone (PS) HD membranes was effectively inhibited by α-tocopherol and glycyrrhizin. α-Tocopherol, but not glycyrrhizin, was found to inhibit PS membrane-induced P-selectin expression on the platelet surface; however, glycyrrhizin did inhibit both the formation of neutrophil-platelet microaggregates induced by adenosine diphosphate (ADP) and the adhesion of HL60 leukemic cells to P-selectin-expressing Chinese hamster ovary (CHO) cells, suggesting that glycyrrhizin acts as a competitive inhibitor of P-selectin-mediated cell adhesion. Finally, these compounds almost completely abrogated PS membrane-induced and platelet-dependent ROS production by neutrophils.

Conclusions

These results suggest that α-tocopherol and glycyrrhizin may function as preventive agents of HD-associated leukocyte activation though the modulation of platelet-leukocyte interaction.

Suilysin-induced Platelet-Neutrophil Complexes Formation is Triggered by Pore Formation-dependent Calcium Influx

Platelet activation and platelet–neutrophil interactions have been found to be involved in inflammation, organ failure and soft-tissue necrosis in bacterial infections. Streptococcus suis, an emerging human pathogen, can cause streptococcal toxic-shock syndrome (STSS) similarly to Streptococcus pyogenes. Currently, S. suis–platelet interactions are poorly understood. Here, we found that suilysin (SLY), the S. suis cholesterol-dependent cytolysin (CDC), was the sole stimulus of S. suis that induced platelet-neutrophil complexes (PNC) formation. Furthermore, P-selectin released in α-granules mediated PNC formation. This process was triggered by the SLY-induced pore forming-dependent Ca²⁺ influx. Moreover, we demonstrated that the Ca²⁺ influx triggered an MLCK-dependent pathway playing critical roles in P-selectin activation and PNC formation, however, PLC-β-IP3/DAG-MLCK and Rho-ROCK-MLCK signalling were not involved. Additionally, the “outside-in” signalling had a smaller effect on the SLY-induced P-selectin release and PNC formation. Interestingly, other CDCs including pneumolysin and streptolysin O have also been found to induce PNC formation in a pore forming-dependent Ca²⁺ influx manner. It is possible that the bacterial CDC-mediated PNC formation is a similar response mechanism used by a wide range of bacteria. These findings may provide useful insight for discovering potential therapeutic targets for S. suis-associated STSS.

Dynamic contributions of P- and E-selectins to β2-integrin-induced neutrophil transmigration

Leukocyte transendothelial migration is a key step in their recruitment to sites of inflammation. However, synergic regulation of endothelium-expressed selectins on leukocyte transmigration remains unclear. In this study, an in vitro model was developed to investigate the dynamic contributions of P- and E-selectin to polymorphonuclear neutrophil (PMN) transmigration under static conditions. Human umbilical vein endothelial cells (HUVECs) were treated with LPS for 4 or 12 h to induce different expression of selectins and intercellular adhesion molecule (ICAM)-1. PMN transmigration was increased significantly by LPS stimulation, which was higher on 4-h than on 12-h LPS-treated HUVECs. Blocking and competitive tests indicated that P-selectin engages PSGL-1 to activate β₂-integrin and initiate PMN transmigration within the first 15 min, whereas E-selectin engages CD44 to influence PMN transmigration after 15 min. P- and E-selectin-induced β₂-integrin activation is likely conducted through the spleen tyrosine kinase signaling pathway. Complicated complementary and competitive mechanisms are involved in the interaction of P-/E-selectins and their ligands to promote PMN transmigration. These results provide direct evidence of the distinct and dynamic contribution of P- and E-selectins in mediating PMN transmigration and give new insight into PMN interaction with the vessel wall.-Gong, Y., Zhang, Y., Feng, S., Liu, X., Lü, S., Long, M. Dynamic contributions of P- and E-selectins to β₂-integrin-induced neutrophil transmigration.

Thrombin-Mediated Platelet Activation of Lysed Whole Blood and Platelet-Rich Plasma: A Comparison Between Platelet Activation Markers and Ultrastructural Alterations

Platelet ultrastructural alterations representing spurious activation have been identified in pathological conditions. A limitation of platelet studies is that sample preparation may lead to artifactual activation processes which may confound results, impacting the use of scanning electron microscopy as a supplemental diagnostic tool. We used scanning electron microscopy and flow cytometry to analyze platelet activation in platelet-rich plasma (PRP) and whole blood (WB) samples. PRP generated using a single high g force centrifugation, and WB samples treated with a red blood cell lysis buffer, were exposed to increasing concentrations of the agonist thrombin. Platelets in lysed WB samples responded to thrombin by elevating the activation marker CD62p definitively, with corresponding ultrastructural changes indicating activation. Conversely, CD62p expression in PRP preparations remained static. Ultrastructural analysis revealed fully activated platelets even under low concentration thrombin stimulation, with considerable fibrin deposition. It is proposed that the method for PRP production induced premature platelet activation, preventable by using an inhibitor of platelet aggregation and fibrin polymerization. Nevertheless, our results show a definitive correspondence between flow cytometry and scanning electron microscopy in platelet activation studies, highlighting the potential of the latter technique as a supplemental diagnostic tool.

Pulmonary Protection Strategies in Cardiac Surgery: Are We Making Any Progress?

Pulmonary dysfunction is a common complication of cardiac surgery. The mechanisms involved in the development of pulmonary dysfunction are multifactorial and can be related to the activation of inflammatory and oxidative stress pathways. Clinical manifestation varies from mild atelectasis to severe respiratory failure. Managing pulmonary dysfunction postcardiac surgery is a multistep process that starts before surgery and continues during both the operative and postoperative phases. Different pulmonary protection strategies have evolved over the years; however, the wide acceptance and clinical application of such techniques remain hindered by the poor level of evidence or the sample size of the studies. A better understanding of available modalities and/or combinations can result in the development of customised strategies for the different cohorts of patients with the potential to hence maximise patients and institutes benefits.

Benzophenone-based photochemical micropatterning of biomolecules to create model substrates and instructive biomaterials

The extracellular matrix (ECM) is a dynamic and heterogeneous environment that controls many aspects of cell behavior. Not surprisingly, many different approaches have focused on creating model substrates that recapitulate the biomolecular, topographical, and mechanical properties of the ECM for in vitro studies of cell behavior. This chapter details a general, versatile method for the spatially controlled deposition of multiple biomolecules onto both planar and topographically complex support structures with micrometer resolution. This approach is based upon the well-understood photochemical UV crosslinking of benzophenone (BP) to solution-phase biomolecules. This is a molecularly general strategy that can be utilized to immobilize biomolecules onto any surface prefunctionalized with BP. Examples described herein include modification of planar and corrugated glass substrates as well as collagen-glycosaminoglycan biomaterials configured either as highly porous scaffolds or nonporous membranes with a variety of biomolecular targets, including proteins, glycoproteins, and carbohydrates.

Glycosylation inhibitors efficiently inhibit P-selectin-mediated cell adhesion to endothelial cells

Adhesion molecules play a critical role in the adhesive interactions of multiple cell types in sickle cell disease (SCD). We previously showed that anti-P-selectin aptamer efficiently inhibits cell adhesion to endothelial cells (ECs) and permits SCD mice to survive hypoxic stress. In an effort to discover new mechanisms with which to inhibit P-selectin, we examined the role of glycosylation. P-selectin is a 90 kDa protein but was found to migrate as 90 and 140 kDa bands on gel electrophoresis. When P-selectin isolated from ECs was digested with peptide N-glycosidase F, but not O-glycosidase, the 140 kDa band was lost and the 90 kDa band was enhanced. Treatment of ECs with tunicamycin, an N-glycosylation inhibitor, suppressed CD62P (P-selectin) expression on the cell surface as well as the 140 kDa form in the cytoplasm. These results indicate that the 140 kDa band is N-glycosylated and glycosylation is critical for cell surface expression of P-selectin in ECs. Thrombin, which stimulates P-selectin expression on ECs, induced AKT phosphorylation, whereas tunicamycin inhibited AKT phosphorylation, suggesting that AKT signaling is involved in the tunicamycin-mediated inhibition of P-selectin expression. Importantly, the adhesion of sickle red blood cells (sRBCs) and leukocytes to ECs induced by thrombin or hypoxia was markedly inhibited by two structurally distinct glycosylation inhibitors; the levels of which were comparable to that of a P-selectin monoclonal antibody which most strongly inhibited cell adhesion in vivo. Knockdown studies of P-selectin using short-hairpin RNAs in ECs suppressed sRBC adhesion, indicating a legitimate role for P-selectin in sRBC adhesion. Together, these results demonstrate that P-selectin expression on ECs is regulated in part by glycosylation mechanisms and that glycosylation inhibitors efficiently reduce the adhesion of sRBCs and leukocytes to ECs. Glycosylation inhibitors may lead to a novel therapy which inhibits cell adhesion in SCD.

Effect of air exposure and suction on blood cell activation and hemolysis in an in vitro cardiotomy suction model

Cardiopulmonary bypass (CPB) elicits a systemic inflammatory response. The cause may include surface-induced leukocyte activation and hemolysis. A study was designed to describe the effects of both suction and an air-blood interface independently and in combination on leukocyte and platelet activation, and hemolysis in an in vitro model. Fresh human blood was drawn and tested in four different conditions including control (A), 10 minutes of -600 mm Hg suction (B), 10 minutes of blood exposure to room air at 100 ml/min (C), and 10 minutes of simultaneous suction and air flow (D). Samples were analyzed by flow cytometry (platelets and leukocytes) and plasma-free hemoglobin (PFHb). Leukocyte CD11b expression and platelet P-selectin (CD62P) were analyzed by flow cytometry. In comparison with baseline, granulocytes were significantly activated by air (group C, p = 0.0029) and combination (group D, p = 0.0123) but not by suction alone (group B). Monocytes and platelets were not significantly activated in any group. The PFHb increased significantly in group C (p < 0.001) and group D (p < 0.001). This study suggests that the inflammatory response and associated hemolysis during CPB may be related to air exposure, which could be reduced by minimizing the air exposure of air to blood during cardiotomy suction.

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.

Cytokine secretion from human monocytes potentiated by P-selectin-mediated cell adhesion

BACKGROUND/AIM

P-selectin is a carbohydrate-recognizing cell adhesion molecule expressed on activated platelets and endothelial cells. It plays a crucial role in the recruitment of leukocytes to inflammatory and hemorrhagic sites. Cell adhesion mediated by P-selectin induces leukocyte activation, such as the generation of reactive oxygen species and the expression of blood coagulation factors. We assessed how P-selectin-mediated cell adhesion affects cytokine secretion from monocytes.

METHODS

Human peripheral blood monocytes were cultured in a plate that had been coated with P-selectin purified from human platelets, and cytokines released in the culture supernatant from monocytes were determined by ELISA.

RESULTS

The secretion of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-8, IL-12 and macrophage inflammatory protein-1β increased 3- to 10-fold in response to P-selectin compared with unstimulated monocytes. We next examined the effects of cytokine treatment of monocytes on their susceptibility to P-selectin. The secretion of TNF-α from monocytes in response to P-selectin was increased when monocytes were preincubated with granulocyte/macrophage colony-stimulating factor, monocyte chemotactic protein-1 or interferon-γ (IFN-γ); IFN-γ was the most effective in potentiating TNF-α secretion from monocytes.

CONCLUSION

These results suggest that the interaction of monocytes with P-selectin plays an important role not only in their trafficking but also in the regulation of cytokine production by these cells.

Probing dynamic cell-substrate interactions using photochemically generated surface-immobilized gradients: application to selectin-mediated leukocyte rolling

Model substrates presenting biochemical cues immobilized in a controlled and well-defined manner are of great interest for their applications in biointerface studies that elucidate the molecular basis of cell receptor-ligand interactions. Herein, we describe a direct, photochemical method to generate surface-immobilized biomolecular gradients that are applied to the study of selectin-mediated leukocyte rolling. The technique employs benzophenone-modified glass substrates, which upon controlled exposure to UV light (350-365 nm) in the presence of protein-containing solutions facilitate the generation of covalently immobilized protein gradients. Conditions were optimized to generate gradient substrates presenting P-selectin and PSGL-1 (P-selectin glycoprotein ligand-1) immobilized at site densities over a 5- to 10-fold range (from as low as ∼200 molecules μm(-2) to as high as 6000 molecules μm(-2)). The resulting substrates were quantitatively characterized via fluorescence analysis and radioimmunoassays before their use in the leukocyte rolling assays. HL-60 promyelocytes and Jurkat T lymphocytes were assessed for their ability to tether to and roll on substrates presenting immobilized P-selectin and PSGL-1 under conditions of physiologically relevant shear stress. The results of these flow assays reveal the combined effect of immobilized protein site density and applied wall shear stress on cell rolling behavior. Two-component substrates presenting P-selectin and ICAM-1 (intercellular adhesion molecule-1) were also generated to assess the interplay between these two proteins and their effect on cell rolling and adhesion. These proof-of-principle studies verify that the described gradient generation approach yields well-defined gradient substrates that present immobilized proteins over a large range of site densities that are applicable for investigation of cell-materials interactions, including multi-parameter leukocyte flow studies. Future applications of this enabling methodology may lead to new insights into the biophysical phenomena and molecular mechanism underlying complex biological processes such as leukocyte recruitment and the inflammatory response.

Platelets as central mediators of systemic inflammatory responses

Systemic inflammatory responses are associated with high morbidity and mortality and represent a diverse and clinically challenging group of diseases. Platelets are increasingly linked to inflammation, in addition to their well-known roles in hemostasis and thrombosis. There is agreement that traditional functions of platelets, including adherence, aggregation, and secretion of preformed mediators, contribute to systemic inflammatory responses. However, emerging evidence indicates that platelets function in non-traditional ways. In this review, we focus on new functions of platelets that may be involved in the host response to infection.

Platelet proinflammatory activity in clinically stable patients with CF starts in early childhood

BACKGROUND

Early onset chronic inflammation is present in CF. Platelets may contribute to inflammation by cytokine release and interaction with leukocytes.

METHODS

Parameters of platelet proinflammatory function (soluble CD62P, soluble CD40L, the percentage of platelet-leukocyte aggregates, platelet CD62P) and platelet procoagulatory function (PAC-1-binding to activated integrin alpha(IIb)beta(3) and expression of integrin alpha(IIb)beta(3)=CD41a) were measured in patients and controls.

RESULTS

Levels of sCD62P, sCD40L were increased in CF irrespective of age and activity of inflammation. The number of platelet-leukocyte aggregates was elevated in older CF patients. PAC-1-binding to platelets decreased with growing activity of inflammation. Exocytosis of CD41a upon platelet activation was reduced.

CONCLUSION

In CF, platelet proinflammatory activity is increased at very young age already and might promote inflammation and tissue damage. On the other hand, platelets seem to downregulate the activation of their most important integrin (alpha(IIb)beta(3)) for clot formation.

P-selectin-dependent platelet aggregation and apoptosis may explain the decrease in platelet count during Helicobacter pylori infection

P-selectin expression has been shown in Helicobacter pylori-infected persons, an infection that has been clinically associated with platelet-related diseases, such as idiopathic thrombocytopenic purpura. However, the role of P-selectin expression during H pylori infection remains unclear. In this study, we hypothesized that P-selectin expression was associated with platelet aggregation during H pylori infection. Using flow cytometry, we examined the levels of adhesion between H pylori and platelets as well as the levels of P-selectin expression and platelet phosphatidylserine (PS) expression during H pylori infection. Significantly high levels of adhesion between pro-aggregatory bacteria and platelets were observed. We identified that H pylori IgG is required for bacteria to induce P-selectin expression and that a significant release of P-selectin is essential for H pylori to induce aggregation. In addition, cellular apoptotic signs, such as membrane blebbing, were observed in platelet aggregates. PS expression was also detected in platelets during infection with both pro-aggrogatory and nonaggregatory strains of H pylori. These results suggest that the decrease in platelet counts seen during H pylori infection is the result of P-selection-dependent platelet aggregation and PS expression induced by the bacteria.

Endoplasmic reticulum HSP90b1 (gp96, grp94) optimizes B-cell function via chaperoning integrin and TLR but not immunoglobulin

Endoplasmic reticulum (ER) unfolded protein response (UPR) plays pivotal roles in both early B-cell development and plasma cell differentiation. As a major ER chaperone to mediate the UPR and a master chaperone for Toll-like receptors (TLRs), HSP90b1 (grp94, gp96) has long been implicated to facilitate the assembly of immunoglobulin. We hereby critically and comprehensively examine the roles of HSP90b1 in B-cell biology in vivo using B-cell-specific HSP90b1-null mice. We found that knockout B cells developed normally. There were no apparent problems with plasma cell differentiation, Ig assembly, class-switching, and Ig production. Strikingly, although both mutant conventional and innatelike B cells failed to compartmentalize properly due to loss of select but not all integrins, HSP90b1 was required for neither germinal center formation nor memory antibody responses in vivo. The only significant defect associated with HSP90b1 ablation in B cells was an attenuated antibody production in the context of TLR stimulation. Thus, our study has resolved the long-standing question regarding HSP90b1 in B-cell biology: HSP90b1 optimizes the function of B cells by chaperoning TLRs and integrins but not immunoglobulin. This study also has important implications in resolving the controversial roles of TLR in B-cell biology.

Redistribution of P-selectin ligands on neutrophil cell membranes and the formation of platelet-neutrophil complex induced by hemodialysis membranes

The formation of platelet-neutrophil microaggregates and successive activation of neutrophils are closely related to hemodialysis-associated complications. The microaggregate is mediated primarily by the interaction between P-selectin (CD62P) expressed on activated platelets and P-selectin glycoprotein ligand-1 (PSGL-1, CD162) expressed on neutrophils. We previously reported that the clustered distribution of PSGL-1 on the cell membranes of chemokine-treated neutrophils caused upregulation of the microaggregate formation. In this study, we found that neutrophils treated with human plasma that had been incubated with hemodialysis membranes greatly enhanced the microaggregate formation. The membrane-treated plasma also induced PSGL-1 to form a cap-like cluster on the neutrophil surface. Analysis of several hemodialysis membranes with different materials indicated that the inducibility for the cap-like cluster formation of PSGL-1 parallels their ability to activate the complement system. Both the enhancement of microaggregate formation and the redistribution of PSGL-1 induced by the hemodialysis membrane-treated plasma were almost completely abrogated in the presence of a specific antagonist for the complement component C5a receptor, W-54011. These results strongly suggest that the generation of anaphylatoxin C5a through complement activation induced by hemodialysis membranes is responsible for the clustered redistribution of PSGL-1 in neutrophils leading to the increase in the platelet-neutrophil microaggregate formation. The present study indicates the importance of synergistic exacerbation of complement activation and platelet-neutrophil microaggregate formation in developing hemodialysis-associated complications.

Nanomechanical control of cell rolling in two dimensions through surface patterning of receptors

We envisioned that label-free control of the transport of cells in two dimensions through receptor-ligand interactions would enable simple separation systems that are easy to implement yet retain the specificity of receptor-ligand interactions. Here we demonstrate nanomechanical control of cell transport in two dimensions via transient receptor-ligand adhesive bonds by patterning of receptors that direct cell rolling through an edge effect. HL-60 cells rolling on P-selectin receptor patterns were deflected at angles of 5-10 degrees with respect to their direction of travel. Absence of this effect in the case of rigid microsphere models of cell rolling suggests that this two-dimensional motion depends on nanomechanical properties of the rolling cell. This work suggests the feasibility of simple continuous-flow microfluidic cell separation systems that minimize processing steps and yet retain the specificity of receptor-ligand interactions.

Radiation-guided P-selectin antibody targeted to lung cancer

PURPOSE

P-selectin expression is significantly increased in tumor microvasculature following exposure to ionizing radiation. The purpose of this study was to image radiation-induced P-selectin expression in vivo using optical imaging and gamma camera imaging in a heterotopic lung cancer model by using ScFv antibodies to P-selectin.

PROCEDURES

In vitro studies using endothelial cells were done using 3 Gy radiation and selected ScFv antibodies to P-selectin. In vivo studies were performed using Lewis lung carcinoma cells subcutaneously injected into the hind limbs of nude mice. Mice were treated with 6 Gy radiation and sham radiation 10 days post-inoculation. P-selectin expression was assessed with near-infrared imaging using Cy7 labeled antibody, and gamma camera imaging using( 111)In-DTPA labeled antibody.

RESULTS

In vitro studies showed antibody binding to P-selectin in radiation treated endothelial cells. In vivo optical imaging and gamma camera imaging studies showed significant tumor-specific binding to P-selectin in irradiated tumors compared to unirradiated tumors.

CONCLUSIONS

Optical imaging and gamma camera imaging are effective methods for visualizing in vivo targeting of radiation-induced P-selectin in lung tumors. This study suggests that fluorescent-labeled and radiolabeled ScFv antibodies can be used to target radiation-induced P-selectin for the tumor-specific delivery of therapeutic drugs and radionuclides in vivo.

Immunology

The concept of forbidden foods that should not be eaten goes back to the Garden of Eden and apart from its religious meanings it may also have foreshadowed the concept of foods that can provoke adverse reactions. Thus we could say that allergic diseases have plagued mankind since the beginning of life on earth. The prophet Job was affected by a condition that following the rare symptoms described by the Holy Bible might be identified as a severe form of atopic dermatitis (AD). The earliest record of an apparently allergic reaction is 2621 B.C., when death from stinging insects was first described by hieroglyphics carved into the walls of the tomb of Pharaoh Menes depicting his death following the sting of a wasp. In 79 A.D., the death of the Roman admiral Pliny the Elder was ascribed to the SO₂-rich gases emanating from the eruption of Mount Vesuvius. Hippocrates (460–377 B.C.) was probably the first to describe how cow’s milk (CM) could cause gastric upset and hives, proposing dietetic measures including both treatment and prevention for CM allergy.

Adhesion characteristics and stability assessment of lectin-modified liposomes for site-specific drug delivery

Carbohydrate moieties of the cellular glycocalyx have been suggested to play an important role in biological recognition processes during pathologic conditions, such as inflammation and cancer. Herein, we describe lectin-modified liposomes which might have potential for site-specific drug delivery during the therapy of such diseases. Specific interactions of plain (i.e., unmodified) and PEGylated, lectin-grafted liposomes with model membranes were investigated under real-time flow conditions using a quartz crystal microbalance. In addition, the morphology of the liposomal systems was assessed by atomic force microscopy. Plain liposomes exhibited only unspecific adhesion to glycolipid membranes and had a tendency to coalesce. The degree of membrane interaction was significantly increased when plain liposomes were modified with the lectin, Concanavalin A. However, vesicle fusion also markedly increased as a result of lectin modification. Additional PEGylation of liposomes reduced unspecific adhesion phenomena, as well as coalescence. Moreover, our studies enabled us to establish quartz crystal microbalance and atomic force microscopy as powerful and complementary methods to characterize adhesion properties of targeted drug delivery systems.

Redistribution of P-selectin glycoprotein ligand-1 (PSGL-1) in chemokine-treated neutrophils: a role of lipid microdomains

P-selectin glycoprotein ligand-1 (PSGL-1) is a mucin-like cell adhesion molecule expressed on leukocyte plasma membranes and involved in platelet-leukocyte and endothelium-leukocyte interactions. The treatment of neutrophils with a low concentration of IL-8 induced the redistribution of PSGL-1 to one end of the cell to form a cap-like structure. We investigated the role of lipid microdomains in the redistribution of PSGL-1 and its effect on the adhesive characteristics of IL-8-treated neutrophils. The redistribution of PSGL-1 induced by IL-8 was inhibited by cholesterol-perturbing agents such as methyl-beta-cyclodextrin and filipin. Sucrose density gradient centrifugation analysis revealed that PSGL-1 was enriched in a low-density fraction together with the GM1 ganglioside after solubilization of the cell membranes with a nonionic detergent, Brij 58. However, when Triton X-100 was used for the solubilization, PSGL-1 was no longer recovered in the low-density fraction, although GM1 ganglioside remained in the low-density fraction. Furthermore, immunofluorescence microscopic observation demonstrated that the localization of PSGL-1 differed from that of GM1 ganglioside, suggesting that PSGL-1 is associated with a microdomain distinct from that containing the GM1 ganglioside. Treatment of neutrophils with IL-8 increased the formation of microaggregates composed of neutrophils and activated platelets, and this treatment also enhanced reactive oxygen species production in neutrophils induced by the cross-linking of PSGL-1 with antibodies. These results suggest that the association of PSGL-1 with lipid microdomains is essential for its redistribution induced by IL-8 stimulation and that the redistribution modulates neutrophil functions mediated by interactions with P-selectin.

Fucosylation of serum α1-acid glycoprotein in rheumatoid arthritis patients treated with infliximab

To analyze fucosylation of alpha(1)-acid glycoprotein (AGP) and to identify relations between AGP fucosylation and clinical and biochemical indices of disease activity in patients with rheumatoid arthritis (RA) treated with monoclonal antitumor necrosis factor (TNF) antibody infliximab, we examined 22 patients with RA who underwent a 54-week treatment with infliximab according to ATTRACT protocol. Blood samples were collected at baseline and before every infusion of infliximab. AGP fucosylation was measured using lectin-binding enzyme-linked immunosorbent assay utilizing fucose-specific lectin Aleuria aurantia (AAL). Moreover, the clinical status/activity, erythrocyte sedimentation rate, serum C-reactive protein (CRP), antitrypsin, alpha(1)-antichymotrypsin, AGP reactivity with concanavalin A, serum C3 and C4 complement components, and serum concentrations of TNF and soluble TNF type 1 and type 2 receptors were determined. In most patients, the fucosylation of AGP decreased rapidly after first infusion of infliximab and remained low during the 54-week therapy (p < 0.001). The decrease in AGP affinity to AAL closely followed changes in clinical and laboratory activity of RA and correlated with pretreatment concentrations of CRP (r = 0.4986, p < 0.05) and TNF (r = 0.5181, p < 0.05). The fucosylation of AGP can be a part of a negative feedback loop regulating migration of inflammatory cells and collagenase-3 activity in RA. The decrease in AGP fucosylation accompanied by improvement in clinical and biochemical parameters of RA could possibly reflect reduced migration of inflammatory cells to inflamed joints and AGP-mediated inhibition of collagenase-3 as a response to infliximab treatment.

Characteristics of two CD75-related cell-surface expressed antigens of human lymphocytes

The structure of cell surface carbohydrates expressed on human leukocytes is dependent on the cell's developmental stage, differentiation, and activation. Although modification of oligosaccharide side chains by sialylation is quite common, antigenic determinants on lymphocytes associated with the presence of sialoglycans are still incompletely defined. In the study presented here, monoclonal antibodies (mAbs) were used to characterize two novel but related cell surface carbohydrate antigens. One antigen, denominated as B8, is largely masked by sialyl residues on most lymphocytes, while it is detectable on the majority of B cells. Treatment with sialidase resulted in the exposure of B8 on the surface of blood cells including lymphocytes. Although the second carbohydrate antigen, C1, was sialidase-sensitive, its molecular properties and cellular distribution place it in close vicinity to B8. B8(+) as well as C1(+) lymphocytes were found predominantly in the mantle zone of secondary follicles of tonsillar tissue. These findings raised the possibility that B8 and C1 are closely related to a category of carbohydrate antigens previously classified as CDw76 (recently assigned to CD75s). MAbs directed against B8 or C1 precipitated 34, 37, 43, and 200kDa glycoproteins from tonsillar lymphocytes, indicating that identical cell surface proteins are associated with both antigens. In contrast to B8, however, the expression of C1 was increased on lymphocytes upon activation. Together the results suggest that CD75-related epitopes are distinct molecular entities which may be exposed on glycoproteins and are differently expressed on lymphocytes.

Simultaneous tether extraction contributes to neutrophil rolling stabilization: a model study

Neutrophil rolling is the initial step of neutrophil recruitment to sites of inflammation. During the rolling, membrane tethers are very likely extracted from both the neutrophil and the endothelial cell lining of vessel walls. Here, we present a two-dimensional neutrophil-rolling model to investigate whether and how membrane tethers contribute to stable neutrophil rolling. In our model, neutrophils are assumed to be rigid spheres covered with randomly distributed deformable microvilli, and endothelial cells are modeled as flat membrane surfaces decorated with evenly distributed ligands. The instantaneous rolling velocity and other unknowns of the model are calculated by coupling the hydrodynamic resistance functions, the geometric relationships, and the constitutive equations that govern microvillus extension and tether extraction. Our results show that glutaraldehyde-fixed neutrophils (without microvillus extension or tether extraction) roll unstably on a P-selectin-coated substrate with large variance in rolling velocity. In contrast, normal neutrophils roll much more stably, with small variance in rolling velocity. Compared with tether extraction from the neutrophil alone, simultaneous tether extraction from the neutrophil and endothelial cell greatly increases the lifetime of the adhesive bond that mediates the rolling, allows more transient tethers to make the transition into stable rolling, and enables rolling neutrophils to be more shear-resistant.

Tissue inhibitor of metalloproteinase-2 inhibits T-cell infiltration and preserves pancreatic β-cell function in an in vitro type 1 diabetes mellitus model

Type 1 diabetes mellitus (T1DM) results from autoreactive T-cells that attack and destroy insulin producing pancreatic beta-cells. This knowledge has provided a framework for numerous efforts to prevent or mitigate T1DM at various stages of the disease. In this study, we utilized an organ culture model of type 1 diabetes to determine whether tissue inhibitors of metalloproteinases (TIMPs) could block T-cell migration into the pancreas and ultimately preserve beta-cell function. We measured T-cell repertoires, insulin secretion, and performed immunohistochemistry and confocal laser microscopy in order to evaluate the effect of TIMP-1, TIMP-2, and TIMP-3 on our in vitro T1DM organ culture model. TIMP-2 decreased T-cell transmigration and preserved insulin production in our T1DM organ culture model. Moreover, TIMP-2 inhibited transmigration of diabetogenic T-cells across an islet microvascular endothelial cell layer. Our findings suggest that TIMP-2 is effective at blocking infiltration of autoreactive T-cells into target pancreas tissue thereby preserving pancreatic beta-cell mass.

Cellular, molecular and immunological mechanisms in the pathophysiology of vein graft intimal hyperplasia

Coronary artery disease, leading to myocardial infarction and ischaemia, affects millions of persons and is one of the leading causes of morbidity and mortality worldwide. Invasive techniques such as coronary artery bypass grafting are used to alleviate the sequelae of arterial occlusion. Unfortunately, restenosis or occlusion of the grafted conduit occurs over a time frame of months to years with a gradual reduction in patency, especially in vein grafts. The events leading to intimal hyperplasia (IH) formation involve numerous cellular and molecular components. Various cellular elements of the vessel wall are involved as are leucocyte-endothelial interactions that trigger the coagulation cascade leading to localized thrombus formation. Subsequent phenotypic modification of the medial smooth muscle cells and their intimal migration is the basis of the lesion formation that is thought to be propagated by an immune-mediated reaction. Despite intense scrutiny, the pathophysiology of IH remains an enigma. Although several growth factors, cytokines and numerous other biomolecules have been implicated and their relationship to prohyperplasia pathways such as the phosphatidyl-inositol 3-kinase (PI3K)-Akt pathway has been established, many pieces of the puzzle are still missing. An in-depth understanding of early vein graft adaptation and progression is necessary to improve the long-term prognosis and develop more effective therapeutic measures. In this review, we have critically evaluated and summarized the literature to elucidate and interlink the numerous established and emerging factors that play a key role in the development of IH leading to vein graft restenosis.

Tick lectins: structural and functional properties

Few papers have been published on tick lectins so far, and therefore more data are needed to complete the mosaic of knowledge of their structural and functional properties. Tissue-specific lectin/haemagglutinin activities of both soft and hard ticks have been investigated. Some tick lectins are proteins with binding affinity for sialic acid, various derivatives of hexosamines and different glycoconjugates. Most tick lectin/haemagglutinin activities are blood meal enhanced, and could serve as molecular factors of self/non-self recognition in defence reactions against bacteria or fungi, as well as in pathogen/parasite transmission. Dorin M, the plasma lectin of Ornithodoros moubata, is the first tick lectin purified so far from tick haemolymph, and the first that has been fully characterized. Partial characterization of other tick lectins/haemagglutinins has been performed mainly with respect to their carbohydrate binding specificities and immunochemical features.

Oxidative stress and adhesion molecules in children with type 1 diabetes mellitus: a possible link

OBJECTIVE

To examine whether oxidative stress parameters were correlated with adhesion molecules derived from endothelial/platelet activation in a group of juveniles with type 1 diabetes mellitus (T1DM).

SUBJECTS AND METHODS

Indicative parameters of patient oxidant/antioxidant capacity were measured and associated with P-selectin and tetranectin (TN), markers of endothelial/platelet activation, in the plasma of 45 diabetic children and adolescents and 20 healthy age-matched subjects (HS).

RESULTS

Significantly, higher nitrate/nitrite (NOx) and lipid hydroperoxide (LPO) levels (p=0.049 and p=0.0011, respectively), lower glutathione peroxidase activity (GPx; p=0.038), and elevated TN and P-selectin plasma levels (p=0.0046 and p=0.042, respectively) were found in T1DM children compared with HS. Well-controlled T1DM children (HbA1c <or= 7%) showed significantly lower GPx (p=0.0259), higher NOx and LPO (p=0.01093 and p=0.0092, respectively) compared with HS, while poorly controlled patients (HbA1c >7%) showed significantly higher TN, sP-selectin and LPO (p=0.0064, p=0.0234 and p=0.0121, respectively), a tendency to higher NOx (p=0.063) compared with HS and only TN higher (p=0.0123) compared with well-controlled patients. Patients with shorter diabetes duration (<or=3 yr) showed significantly higher LPO and TN (p=0.034 and 0.017, respectively), a tendency to higher NOx and lower GPx and higher P-selectin, while those with longer duration (>3 yr) differed significantly in all the examined parameters (TN, p=0.0015; GPx, p=0.0420; NOx, p=0.0196; LPO, p=0.0054; sP-selectin, p=0.0187) compared with HS.

CONCLUSIONS

Decreased antioxidative protection from simultaneous LPO and NOx overproduction is evident in T1DM juveniles with a parallel endothelial/platelet activation even in the first years of the disease, being more pronounced later in diabetes progression, contributing to the vascular complications of the disease.

Raised Plasma Soluble P-Selectin in Peripheral Arterial Occlusive Disease Enhances Leukocyte Adhesion

Raised levels of soluble P-selectin (sP-selectin) have been reported in the plasma of patients with vascular diseases; however, the functional importance of this ligand remains unclear. In this study we have examined a potential role for plasma sP-selectin in regulating neutrophil adhesion in patients with peripheral arterial occlusive disease (PAOD). Patients with PAOD had significantly higher levels of sP-selectin (mean±SD: 73.3±13.0 versus 16.7±6.4 ng/mL) and enhanced whole blood leukocyte adhesion to platelets under shear. To examine whether the raised sP-selectin levels can directly influence leukocyte adhesion, isolated neutrophils were incubated with plasma from PAOD patients before and after immunodepletion of sP-selectin. Neutrophil adhesion to fibrinogen increased 2-fold following incubation with PAOD plasma, which was abrogated on sP-selectin immunodepletion. We subsequently demonstrated that recombinant sP-selectin dose-dependently (75 to 250 ng/mL) increased leukocyte adhesion to fibrinogen and platelet monolayers. This increase was PSGL-1 and Src kinase-dependent and correlated with an increase in sP-selectin-mediated Mac-1 activation. sP-selectin–stimulated neutrophil adhesion to platelet monolayers was inversely correlated with shear, such that at low shear (50 s −1 ) a 92.7%±15.7 increase in adhesion was observed decreasing to 38.5%±11.9 at 150 s −1 and 10.1%±7.4 at 300 s −1 . These studies suggest a potentially important role for sP-selectin in modulating neutrophil adhesion in patients with PAOD, particularly at sites of low shear, where it raises the possibility that raised plasma sP-selectin levels may enhance leukocyte recruitment to vascular injury and promote disease progression.