Investigation of platelet-neutrophil interactions in whole blood by flow cytometry

Evaluation of a simultaneous adsorption device for cytokines and platelet-neutrophil complexes in vitro and in a rabbit acute lung injury model

Background

Platelet–neutrophil complexes (PNCs) readily migrate into tissues and induce tissue damage via cytokine or other pathogenic factors release. These actions are involved in onset and progression of acute respiratory distress syndrome (ARDS). Thus, simultaneous removal of cytokines and activated neutrophils, including PNCs by blood purification may prevent development of ARDS and enhance drug effects. The goal of this study was to examine the effect of a newly developed adsorption column (NOA-001) that eliminates cytokines and activated neutrophils in a lung injury model.

Results

Adsorption of cytokines, such as IL-8, IL-6 and HMGB-1, and PNCs was first measured in vitro. Lung injury was induced by HCl and lipopolysaccharide intratracheal infusion in rabbits ventilated at a low tidal volume (7–8 mL/kg) and PEEP (2.5 cmH₂O) for lung protection. Arterial blood gas, hematologic values, plasma IL-8, blood pressure and heart rate were measured, and lung damage was evaluated histopathologically in animals treated with 8-h direct hemoperfusion with or without use of NOA-001. The in vitro adsorption rates for IL-8, IL-6, HMGB-1, activated granulocytes and PNCs were 99.5 (99.4–99.5)%, 63.9 (63.4–63.9)%, 57.6 (57.4–62.1)%, 9.9 (-4.4–21.3)% and 60.9 (49.0–67.6)%, respectively. Absorption of PNCs onto fibers was confirmed microscopically. These adsorption effects were associated with several improvements in the rabbit model. In respiratory function, the PaO₂/FIO₂ ratios at 8 h were 314 ± 55 mmHg in the NOA-001 group and 134 ± 41 mmHg in the sham group. The oxygenation index and PaCO₂ at 8 h were 9.6 ± 3.1 and 57.0 ± 9.6 mmHg in the sham group and 3.0 ± 0.8 and 40.4 ± 4.5 mmHg in the NOA-001 group, respectively (p < 0.05). Blood pH at 8 h reached 7.18 ± 0.06 in the sham group, but was maintained at 7.36 ± 0.03 (within the normal range) in the NOA-001 group (p < 0.05). In lung histopathology, fewer hyaline membrane and inflammatory cells were observed in the NOA-001 group.

Conclusion

A column for simultaneous removal of cytokines and PNCs showed efficacy for improvement of pulmonary function in an animal model. This column may be effective in support of treatment of ARDS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40635-021-00414-7.

Role of Platelets in Leukocyte Recruitment and Resolution of Inflammation

Platelets are most often recognized for their crucial role in the control of acute hemorrhage. However, current research has greatly expanded the appreciation of platelets beyond their contribution to primary hemostasis, indicating that platelets also actively participate in leukocyte recruitment and the regulation of the host defense in response to exogenous pathogens and sterile injury. Early recruitment of leukocytes, especially neutrophils, is the evolutionary stronghold of the innate immune response to successfully control exogenous infections. Platelets have been shown to physically interact with different leukocyte subsets during inflammatory processes. This interaction holds far-reaching implications for the leukocyte recruitment into peripheral tissues as well as the regulation of leukocyte cell autonomous functions, including the formation and liberation of neutrophil extracellular traps. These functions critically depend on the interaction of platelets with leukocytes. The host immune response and leukocyte recruitment must be tightly regulated to avoid excessive tissue and organ damage and to avoid chronification of inflammation. Thus, platelet-leukocyte interactions and the resulting leukocyte activation and recruitment also underlies tight regulation by several inherited feedback mechanisms to limit the extend of vascular inflammation and to protect the host from collateral damage caused by overshooting immune system activation. After the acute inflammatory phase has been overcome the host defense response must eventually be terminated to allow for resolution from inflammation and restoration of tissue and organ function. Besides their essential role for leukocyte recruitment and the initiation and propagation of vascular inflammation, platelets have lately also been implicated in the resolution process. Here, their contribution to phagocyte clearance, T cell recruitment and macrophage reprogramming is also of outmost importance. This review will focus on the role of platelets in leukocyte recruitment during the initiation of the host defense and we will also discuss the participation of platelets in the resolution process after acute inflammation.

Comparison of capillary and venous blood in the analysis of concentration and function of leucocyte sub-populations

PURPOSE

Compare capillary and venous blood in the analysis of concentration and function of leucocyte sub-populations. This study hypothesised that capillary samples may be used in a site-specific manner as an alternative source of blood samples for assays of leucocyte concentration and neutrophilic phagocytic function and reactive oxygen species (ROS) production, allowing acquisition of multiple samples to better monitor transient but significant post-exercise immune modulation.

METHODS

Resting blood samples were simultaneously obtained from vein, finger and earlobe of healthy subjects (n = 10, age: 25.1 ± 3.1 years). Leucocyte concentrations were measured using a five-part differential haematological analyser. Leucocyte sub-populations (CD3, CD4, CD8, CD19, CD56, CD14) and granulocytic functional-related (CD11b, CD18, CD16b, CD66b) surface antigen markers, neutrophil phagocytosis (FITC-labelled Escherichia coli) and stimulated ROS production (DHR) were quantified utilizing flow cytometry. A MANOVA (α < 0.05 significance) analysed the effects of the different sampling sites in the concentrations of leucocyte populations, their surface antigen expression and granulocytic functions.

RESULTS

Leucocyte concentration and neutrophilic ROS production yielded non-significant differences between sampling sites. Expression of granulocytic surface antigens was increased in both capillary sites compared to venous site (p = 0.008), particularly for adhesion markers CD11b/CD18. The percentage of neutrophils performing phagocytosis was higher in venous samples compared to finger (p = 0.025). Increased number of E. coli ingested was observed in venous sample compared to finger (p = 0.001) and to earlobe (p = 0.006).

CONCLUSION

Whilst attention must be paid for varying neutrophilic surface antigen expression and further studies are needed to establish appropriate reference ranges, this study supports the use of capillary blood samples in a site-specific manner to enhance sampling capabilities field-based research.

Platelet-neutrophil complex formation-a detailed in vitro analysis of murine and human blood samples

Platelets form complexes with neutrophils during inflammatory processes. These aggregates migrate into affected tissues and also circulate within the organism. Several studies have evaluated platelet-neutrophil complexes as a marker of cardiovascular diseases in human and mouse. Although multiple publications have reported platelet-neutrophil complex counts, we noticed that different methods were used to analyze platelet-neutrophil complex formation, resulting in significant differences, even in baseline values. We established a protocol for platelet-neutrophil complex measurement with flow cytometry in murine and human whole blood samples. In vitro platelet-neutrophil complex formation was stimulated with ADP or PMA. We tested the effect of different sample preparation steps and cytometer settings on platelet-neutrophil complex detection and noticed false-positive counts with increasing acquisition speed. Platelet-neutrophil complex formation depends on platelet P-selectin expression, and antibody blocking of P-selectin consequently prevented ADP-induced platelet-neutrophil complex formation. These findings may help generating more comparable data among different research groups that examine platelet-neutrophil complexes as a marker for cardiovascular disease and novel therapeutic interventions.

Platelet-Dependent Neutrophil Function Is Dysregulated by M Protein from Streptococcus pyogenes

Platelets are rapidly responsive sentinel cells that patrol the bloodstream and contribute to the host response to infection. Platelets have been reported to form heterotypic aggregates with leukocytes and may modulate their function. Here, we have investigated platelet-neutrophil complex formation and neutrophil function in response to distinct agonists. The endogenous platelet activator thrombin gave rise to platelet-dependent neutrophil activation, resulting in enhanced phagocytosis and bacterial killing. Streptococcus pyogenes is an important causative agent of severe infectious disease, which can manifest as sepsis and septic shock. M1 protein from S. pyogenes also mediated platelet-neutrophil complex formation; however, these neutrophils were dysfunctional and exhibited diminished chemotactic ability and bacterial killing. This reveals an important agonist-dependent neutrophil dysfunction during platelet-neutrophil complex formation and highlights the role of platelets during the immune response to streptococcal infection.

Platelets in leucocyte recruitment and function

Platelets have a longstanding recognition as an essential cellular component of the coagulation system. However, substantial research over the last decade has added another important aspect to platelet function in that they are also an integral part of the innate immune system. Complex organisms are facing a constant threat of infections by invading pathogens, and they have developed a sophisticated and elegant measure to combat this threat, namely the immune system. Leucocyte recruitment to sites of infections is an essential step at the forefront of the immune response. Platelets have been shown to be involved in several steps of this process and they are an integrated connecting element among haemostasis, host defence, and additional immunological functions (e.g. neutrophil extracellular traps formation). However, the immune system also requires a tight regulation, as an overshooting immune response carries the risk of harming the host itself. This review aims at highlighting the unique features and molecular mechanisms that allow for the interactions of platelets and leucocytes and the regulation of this process. Furthermore, this article identifies the functional relevance of these events for the immune response.

Nutritional Effect of Oral Supplement Enriched in ω-3 Fatty Acids, Arginine, RNA on Immune Response and Leukocyte-platelet Aggregate Formation in Patients Undergoing Cardiac Surgery

The aim of the present study was to investigate the influence of a supplement enriched in ω-3 fatty acids on immune responses and platelet–leukocyte complex formation in patients undergoing cardiac surgery. Patients in the supplement group (n = 7) took a supplement enriched in ω-3 fatty acids (Impact^®) in addition to a hospital diet for five successive days before surgery; those in the control group (n = 7) took only hospital diet and did not take Impact^®. Blood samples in both groups were collected at same time points. Before surgery, samples were collected five days before surgery, at the start of supplementation (baseline), and the end of supplementation (postoperative day (POD)-0). After surgery, samples were collected on POD-1 and POD-7. The expression of human leukocyte antigen (HLA)-DR, the ratio of CD4-/CD8-positive cells, the production of interferon (IFN)-γ by CD4-positive cells, plasma levels of cytokines, and leukocyte–platelet aggregates were measured. Before surgery (POD-0), the supplement caused significant increases in HLA-DR expression, CD4/CD8 ratio, and plasma levels of IFN-γ; these levels were significantly higher compared to those in the control group (P < 0.05, respectively). After surgery (POD-1), all values dramatically decreased in comparison with those of POD-0; however, the values in the supplement group were significantly higher compared to their respective markers in the control group (P < 0.05, respectively). Significant differences of HLA-DR expression and CD4/CD8 ratio persisted through POD-7. Before surgery (POD-0), plasma levels of interleukin (IL)-10 in the supplement group decreased significantly compared with those in the control group (P < 0.05). After surgery (POD-1), plasma levels of IL-10 in both the control and supplement groups increased; these levels in the supplement group were significantly lower than those in the control group (P < 0.05). Significant decreases in the percentage of leukocyte–platelet aggregates were found after supplementation; the difference between the supplement and the control groups was found on POD-0 and POD-1 (P < 0.05, respectively). In conclusion, the dietary supplement increased HLA-DR expression, the CD4/CD8 ratio, and the production of IFN-γ by CD4-positive cells; conversely, the levels of IL-10 and the formation of leukocyte–platelet aggregates before and after surgery were suppressed. These beneficial effects may decrease the incidence of complications after surgery.

Neutrophil and platelet complexes and their relevance to neutrophil recruitment and activation

The manifestation of platelet 'satallitism' around neutrophils in whole blood is a long acknowledged phenomenon [1]. Circulating platelet-neutrophil complexes (PNC) occur in a diverse range of inflammatory disorders and infections that affect numerous organs of the body. Animal models have revealed that the formation of PNC is required for the recruitment of neutrophils to inflamed tissue, since platelets 'prime' neutrophils for efficient adhesion to vascular endothelium via the up-regulation of integrins and enhanced responsiveness to chemokines (Fig. 1). Perhaps surprisingly, the surface contact between platelets and neutrophils additionally enhances other neutrophil functions, such as chemotaxis that is required for migration into tissues, trans-cellular production of eicosanoids, phagocytosis and trapping of pathogens, increased respiratory burst leading to the production of reactive oxygen species (ROS), and modulation of neutrophil apoptosis (Fig. 1). Platelet P-selectin appears to have a particular role in enhancing the majority of these activities, and the influence of platelet P-selectin is not therefore confined to the initial rolling events in the process of neutrophil extravasation.

Effect of aerobic interval training and caffeine on blood platelet function

PURPOSE

Hyperactive platelets contribute to the thrombotic response in humans, and exercise transiently increases platelet function. Caffeine is routinely used by athletes as an ergogenic aid, but the combined effect of exercise and caffeine on platelet function has not been investigated.

METHODS

Twelve healthy males were randomly assigned to one of four groups and undertook four experimental trials of a high-intensity aerobic interval training (AIT) bout or rest with ingestion of caffeine (3 mg·kg(-1)) or placebo. AIT was 8 × 5 min at approximately 75% peak power output (approximately 80% V˙O2peak) and 1-min recovery (approximately 40% peak power output, approximately 50% V˙O2peak) intervals. Blood/urine was collected before, 60, and 90 min after capsule ingestion and analyzed for platelet aggregation/activation.

RESULTS

AIT increased platelet reactivity to adenosine diphosphate (placebo 30.3%, caffeine 13.4%, P < 0.05) and collagen (placebo 10.8%, caffeine 5.1%, P < 0.05) compared with rest. Exercise placebo increased adenosine diphosphate-induced aggregation 90 min postingestion compared with baseline (40.5%, P < 0.05), but the increase when exercise was combined with caffeine was small (6.6%). During the resting caffeine protocol, collagen-induced aggregation was reduced (-4.3%, P < 0.05). AIT increased expression of platelet activation marker PAC-1 with exercise placebo (P < 0.05) but not when combined with caffeine.

CONCLUSION

A single bout of AIT increases platelet function, but caffeine ingestion (3 mg·kg(-1)) does not exacerbate platelet function at rest or in response to AIT. Our results provide new information showing caffeine at a dose that can elicit ergogenic effects on performance has no detrimental effect on platelet function and may have the potential to attenuate increases in platelet activation and aggregation when undertaking strenuous exercise.

Platelet-neutrophil aggregate formation in blood samples from dogs with systemic inflammatory disorders

OBJECTIVE

To evaluate platelet-neutrophil aggregate (PNA) formation and neutrophil shape as indicators of neutrophil activation in dogs with systemic inflammatory diseases and after blood sample incubation with various platelet and neutrophil agonists.

ANIMALS

20 dogs with systemic inflammatory response syndrome (SIRS) and 10 healthy Beagles.

PROCEDURES

Neutrophils were isolated from blood samples directly after blood sample collection and after incubation of blood samples with phorbol myristate acetate, collagen, adenosine diphosphate, epinephrine, or various concentrations of lipopolysaccharide or arachidonic acid. CD61+ neutrophils as an indicator of PNA formation were evaluated, and neutrophil size and granularity were assessed via flow cytometry.

RESULTS

Dogs with SIRS had more PNA formation, larger neutrophil size, and less granularity relative to control dogs, but no differences were evident when these dogs were grouped by whether they had sepsis (n = 6) or disseminated intravascular coagulation (12). A significant increase in PNA formation occurred after neutrophil incubation with all agonists, and incubation with phorbol myristate acetate elicited the strongest response. Neutrophils increased in size and decreased in granularity after incubation with all agonists except epinephrine. Incubation with lipopolysaccharide or arachidonic acid resulted in a dose-dependent effect on PNA formation and neutrophil shape.

CONCLUSIONS AND CLINICAL RELEVANCE

SIRS appeared to increase the degree of PNA formation and neutrophil shape change. Similar changes after neutrophil incubation with platelet agonists suggested that platelet activation has a role in PNA formation. Additional studies are necessary to determine the clinical importance and diagnostic value of PNA formation in dogs with SIRS and sepsis.

Structure-function relationships of human milk oligosaccharides

Human milk contains more than a hundred structurally distinct oligosaccharides. In this review, we provide examples of how the structural characteristics of these human milk oligosaccharides (HMO) determine functionality. Specific α1-2-fucosylated HMO have been shown to serve as antiadhesive antimicrobials to protect the breast-fed infant against infections with Campylobacter jejuni, one of the most common causes of bacterial diarrhea. In contrast, α1-2-fucosylation may abolish the beneficial effects of HMO against Entamoeba histolytica, a protozoan parasite that causes colitis, acute dysentery, or chronic diarrhea. In a different context, HMO need to be both fucosylated and sialylated to reduce selectin-mediated leukocyte rolling, adhesion, and activation, which may protect breast-fed infants from excessive immune responses. In addition, our most recent data show that a single HMO that carries not 1 but 2 sialic acids protects neonatal rats from necrotizing enterocolitis, one of the most common and often fatal intestinal disorders in preterm infants. Oligosaccharides currently added to infant formula are structurally different from the oligosaccharides naturally occurring in human milk. Thus, it appears unlikely that they can mimic some of the structure-specific effects of HMO. Recent advances in glycan synthesis and isolation have increased the availability of certain HMO tri- and tetrasaccharides for in vitro and in vivo preclinical studies. In the end, intervention studies are needed to confirm that the structure-specific effects observed at the laboratory bench translate into benefits for the human infant. Ultimately, breastfeeding remains the number one choice to nourish and nurture our infants.

Effects of various doses of aspirin on platelet activity and endothelial function

Although aspirin has become an established medicine for cardiac and cerebrovascular diseases, the optimal dose remains unknown. We evaluated the optimal dose of aspirin on platelet activity and endothelial function by administering 11 healthy male volunteers (32 ± 6 years of age) doses of aspirin that were increased in a stepwise manner (0, 81, 162, 330 and 660 mg/day) every 3 days. Platelet activity was assessed as surface P-selectin expression (%) measured by flow cytometry and the platelet aggregation ratio. Endothelial function in the brachial artery was assessed by measuring flow-mediated dilation (FMD) before and after reactive hyperemia. Platelet aggregation and P-selectin expression were significantly and dose-dependently suppressed (81-660 mg), and the FMD ratio tended to increase from 0 to 162 mg, but decreased significantly at 660 mg. In conclusion, although aspirin suppressed platelet activity and even surface P-selectin expression, higher doses worsened endothelial-mediated arterial dilation.

Circulating platelet-neutrophil complexes are important for subsequent neutrophil activation and migration

Previous studies in our laboratory have shown that platelets are essential for the migration of eosinophils into the lungs of allergic mice, and that this is dependent on the functional expression of platelet P-selectin. We sought to investigate whether the same is true for nonallergic, acute inflammatory stimuli administered to distinct anatomic compartments. Neutrophil trafficking was induced in two models, namely zymosan-induced peritonitis and LPS-induced lung inflammation, and the platelet dependence of these responses investigated utilizing mice rendered thrombocytopenic. The relative contribution of selectins was also investigated. The results presented herein clearly show that platelet depletion (>90%) significantly inhibits neutrophil recruitment in both models. In addition, we show that P-selectin glycoprotein ligand-1, but not P-selectin, is essential for neutrophil recruitment in mice in vivo, thus suggesting the existence of different regulatory mechanisms for the recruitment of leukocyte subsets in response to allergic and nonallergic stimuli. Further studies in human blood demonstrate that low-dose prothrombotic and pro-inflammatory stimuli (CCL17 or CCL22) synergize to induce platelet and neutrophil activation, as well as the formation of platelet-neutrophil conjugates. We conclude that adhesion between platelets and neutrophils in vivo is an important event in acute inflammatory responses. Targeting this interaction may be a successful strategy for inflammatory conditions where current therapy fails to provide adequate treatment.

Platelets and innate immunity

Although platelets are best known as primary mediators of hemostasis, this function intimately associates them with inflammatory processes, and it has been increasingly recognized that platelets play an active role in both innate and adaptive immunity. For example, platelet adhesive interactions with leukocytes and endothelial cells via P-selectin can lead to several pro-inflammatory events, including leukocyte rolling and activation, production of cytokine cascades, and recruitment of the leukocytes to sites of tissue damage. Superimposed on this, platelets express immunologically-related molecules such as CD40L and Toll-like receptors that have been shown to functionally modulate innate immunity. Furthermore, platelets themselves can interact with microorganisms, and several viruses have been shown to cross-react immunologically with platelet antigens. This review discusses the central role that platelets play in inflammation, linking them with varied pathological conditions, such as atherosclerosis, sepsis, and immune thrombocytopenic purpura, and suggests that platelets also act as primary mediators of our innate defences.

Impact of coincidence on granulocyte-platelet complex determination by flow cytometry is evaluated by a novel computer simulation model of coincidence

Cell complexes composed of two different cells labeled with different fluorophores can be detected as double positive events in the flow cytometer. Double positivity can originate not only from real complexes but from non-interacting coinciding cells as well. Coincidence has a high impact on the determination of the amount of platelet-granulocyte complexes since platelet concentration is in the orders of magnitude higher than that of the granulocytes. A computer model has been developed to simulate coincidence in the flow cytometer to reveal the contribution of coincidence to the overestimation of the total amount of platelet-granulocyte complexes. Mixtures of non-interacting fluorescent beads as well as EDTA-anticoagulated blood samples were analyzed in the flow cytometer. An excellent fit was found between computer simulated and measured data pairs. Bead mixture in the flow cytometer and simulation of that resulted in 37.3+/-1.3 and 35.7+/-0.6% double positivity, respectively. 30.2+/-4.3% double positivity was measured for EDTA-anticoagulated blood samples while simulation of that resulted in 28.3+/-0.6%. Double positivity attributed to platelet-granulocyte complexes in slightly diluted blood samples might originate in coincidence and not from true complexes.

Granulocyte– and monocyte–platelet adhesion index in coronary and peripheral blood after extracorporeal circulation and reperfusion

BACKGROUND

Neutrophil-granulocyte and mononuclear-cell functional changes occur during cardiopulmonary bypass and cardiovascular surgery. In particular, leukocyte-platelet interaction, leading to generation of heterotypic coaggregates, represents an amplification mechanism of the local inflammatory response and tissue damage.

METHODS

Samples of 20 patients were drawn from venous coronary sinus before cardioplegic arrest and immediately after reperfusion, as well as from peripheral blood at 5 and 24 h postoperatively. The granulocyte and monocyte surface expression of CD162, CD15s, CD18, and CD11b were quantified by flow cytometry at the different times. Parallel variations of circulating leukocyte-platelet conjugates (percentages) and a derived (cell number-normalized) leukocyte-platelet adhesion index were measured using a combination of antibodies against CD45, CD14, and CD41a. The evaluation of platelet functional state was carried out using antibodies against CD62P (P-selectin) and PAC-1.

RESULTS

Monocyte and granulocyte cell number increased markedly in coronary blood at reperfusion and in peripheral blood postoperatively when compared with measurements done before cardioplegia. A very different course characterized the changes of the leukocyte-platelet adhesion index with respect to the variations of circulating leukocyte-platelet coaggregates (percentages). Leukocyte molecules expression showed no significant variations for CD15s on both the leukocyte subsets, while a significant up-modulation for CD162 was observed on monocytes at 24 h after extracorporeal circulation (P = 0.0002), and for CD11b on granulocytes at 5 h postoperatively (P = 0.033). A loss of CD162 expression was observed in coronary blood at reperfusion (P = 0.0038) on granulocytes, associated to a down-modulation of CD18 (P = 0.0033) and CD11b (P = 0.0184) in peripheral blood at 24 h postoperatively. No significant up-regulation of platelet activatory molecules expression was found at coronary reperfusion, as well as postoperatively in the peripheral blood, when compared with the before-cardioplegia derived data.

CONCLUSIONS

The over time variations of a normalized leukocyte-platelet adhesion index seem to reflect the cumulative leukocyte-platelet functional interaction more accurately than the parallel measurements of cellular conjugates. The absence of platelet activation suggests that the leukocyte membrane modifications play a main role in controlling the formation and stability of heterotypic leukocyte-platelet coaggregates after cardiac surgery with extracorporeal circulation.

Detection of activated platelets in canine blood by use of flow cytometry

OBJECTIVE

To evaluate whether markers of platelet activation, including P-selectin expression, phosphatidylserine exposure, platelet-leukocyte aggregates, and microparticle formation, could be measured in nonstimulated and stimulated canine blood samples and develop a standardized protocol for detection of activated platelet markers in canine blood.

SAMPLE POPULATION

Blood samples from 10 dogs.

PROCEDURE

Platelet activation was determined by flow cytometric measurement of platelets with P-selectin expression, platelet-leukocyte aggregates, platelet microparticles, and platelets with phosphatidylserine exposure. Changes in specific markers of platelet activation in nonstimulated versus stimulated samples were assessed by use of varying concentrations of 2 platelet agonists, platelet-activating factor (PAF) and adenosine diphosphate. Flow cytometry was used to detect platelet CD61 (glycoprotein IIIa), CD62P (P-selectin), and the leukocyte marker CD45. Annexin V was used to identify exposed phosphatidylserine.

RESULTS

A significant difference was detected in the percentages of platelets with P-selectin, plateletleukocyte aggregates, microparticles, and platelets with annexin V exposure (phosphatidylserine) in samples stimulated with 10nM PAF versus the nonstimulated samples, with platelet-leukocyte aggregates having the greatest difference.

CONCLUSIONS AND CLINICAL RELEVANCE

Platelet activation is essential for thrombus formation and hemostasis and may be potentially useful for evaluation of dogs with suspected thromboembolic disease. Prior to development of a thrombotic state, a prothrombotic state may exist in which only a small number of platelets is activated. Identification of a prothrombotic state by use of activated platelets may help direct medical intervention to prevent a thromboembolic episode.

Confounding effects of platelets on flow cytometric analysis and cell-sorting experiments using blood-derived cells

BACKGROUND

Flow cytometric analysis and cell-sorting of peripheral blood leukocytes is commonplace; however, platelet contamination is typically ignored during immunophenotypic analysis and sorting of blood-derived cells.

METHODS

Red blood cells, platelets, T & B lymphocytes, monocytes, and granulocytes were sorted from rat blood preparations. Presort enrichment was performed by differential centrifugation for all cell types. Additionally, leukocyte samples were prepared by ammonium chloride lysis of red blood cells.

RESULTS

Unless proper precautions were taken, significant numbers of platelets were sorted along with (nonplatelet) cells of interest. The amount of platelet contamination varied greatly from experiment to experiment with the highest level of leukocyte-platelet association observed in the neutrophil/granulocyte population in samples prepared using ammonium chloride-based red blood cell-lysing solution.

CONCLUSIONS

Addition of an immunophenotypic marker for platelet identification is a simple, yet prudent, measure to help evaluate the impact of platelets on immunophenotypic staining when performing flow cytometric analysis or sorting of blood-derived cells and should become a routine practice. Platelet presence in postsort fractions can be due to free platelets as well as target cell-associated platelets and both sources of contamination must be addressed.

Interference of neutrophil-platelet interaction by YC-1: a cGMP-dependent manner on heterotypic cell-cell interaction

N-Formyl-Met-Leu-Phe (fMLP) activated neutrophils and then induced neutrophil-platelet complex formation in co-incubation condition. In addition, fMLP induce intracellular calcium mobilization in platelets, only when it is incubated along with neutrophils. This data established that fMLP-stimulated neutrophils activate platelets. 9E1, a monoclonal antibody of P-selectin, significantly blocks the formation of neutrophil-platelet complex induced by fMLP, indicating the involvement of P-selectin in the neutrophil-platelet complex formation. 3-(5'-hydroxymethyl-2'-furyl-1-benzylindazole (YC-1), an unique nitric oxide-independent activator of soluble guanylate cyclase, was evaluated for its effect on neutrophil-platelet complex. YC-1 inhibits fMLP-induced neutrophil-platelet complex formation in a concentration-dependent manner with an IC50 value of 15.3+/-3.5 microM. However, this effect of YC-1 is partially reversed by pre-treatment of 1H-(1,2,4)oxadiazolo[4,3-a]quinozalin-1-one (ODQ; 10 microM), which is a soluble guanylate cyclase inhibitor. Pre-treatment of either neutrophils or platelets with YC-1 (50 microM) prevent the fMLP-induced neutrophil-platelet complex formation, indicating that YC-1 could potentially exert its effects individually on either neutrophils or platelets alone. Cathepsin G released from fMLP-stimulated neutrophil activates the nearby platelets. YC-1 was also shown to inhibit this release of cathepsin G in a concentration-dependent manner. The IC50 value was 6.2+/-0.2 microM. This inhibitory effect of YC-1 on cathepsin G release is reversed by ODQ (10 microM) and a protein kinase G inhibitor [1-oxo-9.12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-l][1,6]benzodiazocine-10-carbooxylic acid methyl ester (KT5835); 1 microM]. YC-1 inhibits cathepsin G-induced P-selectin expression on human platelet at the IC50 value of 32.5+/-2.6 microM. A further study showed that YC-1 inhibits fMLP-induced neutrophil-platelet complex formation in whole blood at the IC50 value of 35.8+/-8.1 microM in a concentration-dependent manner. According to these data, it was hypothesized that fMLP stimulates neutrophils to release cathepsin G, which subsequently activates the nearby platelets, creating neutrophil-platelet complexes. YC-1 inhibits fMLP-induced neutrophil from releasing cathepsin G via a cGMP-dependent pathway. This inhibitory effect of YC-1 on cathepsin G release is a major mechanism for affecting fMLP-induced neutrophil-platelet complex. YC-1's inhibition P-selectin expression on platelet may potentiate its effects. These inhibitory effects may contribute to the inhibition of neutrophil-platelet complex formation in whole blood.

Association between arterial stiffness and platelet activation

Increased arterial stiffness is strongly associated with atherosclerosis, while platelet activation is an important trigger of thrombotic events in patients with atherosclerosis. However, little is known about the effect of arterial stiffness on platelet activation. We therefore investigated the association between arterial stiffness and platelet activation in 38 normal volunteers (20 men and 18 women) aged 23-77 years (mean = 49 +/- 15 years). Arterial stiffness was assessed by measuring brachial-ankle pulse wave velocity (ba-PWV) and heart-brachial PWV (hb-PWV). Flow cytometric analyses were performed to evaluate platelet activation by measuring surface expression of P-selectin and platelet-neutrophil complexes (PNC) before and after activation by ADP. We also calculated the difference between basal and stimulated states of P-selectin and PNC to assess platelet activation reserve. PWVs were significantly correlated with age and BP (r = 0.60-0.81). For platelet activation and activation reserve, correlations with age were less strong but remained significant (r = 0.36-0.61), with the exception of P-selectin (not significant, NS), and correlations with SBP were similar (r = 0.35-0.53). A significant correlation was found between PWVs and platelet activation (r = 0.43-0.74). Multiple regression analysis demonstrated significant correlations between platelet activation and reserve and PWVs (coefficient = 2.17-6.59), when both age and BP were adjusted for simultaneously. In conclusion, platelet activation was associated with arterial stiffness, suggesting that arterial stiffness may play an important role in thrombotic events.

Human milk oligosaccharides reduce platelet-neutrophil complex formation leading to a decrease in neutrophil beta 2 integrin expression

Human milk is thought by many authorities to be preferable to formula as a source of nutrients for infants. Some of the benefits may stem from its high concentration of unbound oligosaccharides (5-10 g/L). These sugars have structural similarities to selectin ligands, known to mediate important cell-cell interactions in the immune system. Platelet-neutrophil complexes (PNC) exist in healthy individuals but have been implicated in disease states. Formation of these complexes requires selectins and as such, could be influenced by human milk oligosaccharides (HMO). Here, we investigate this possibility by examining the effect of HMO on the formation of PNC and activation of associated neutrophils. We collected blood from 10 healthy volunteers, activated platelets with adenosine 5'-diphosphate, and added HMO, oligosaccharide standards, or phosphate-buffered saline as a control. We determined the influence of HMO on PNC formation and adjacent neutrophil activation with fluorescein-activated cell sorter analysis after labeling with antibodies for the platelet marker CD42a and the neutrophil activation marker CD11b. Within physiologically achievable concentrations (6.25-125 microg/mL), an acidic HMO fraction reduced PNC formation up to 20%, which was similar to the effect seen with high concentrations of sialyl-Lewis x. Associated neutrophils showed a dose-dependent decrease in beta 2 integrin expression, up to 30%, at high but physiological concentrations. The neutral HMO fraction had no effect. These results support the hypothesis that acidic HMO serve as anti-inflammatory components of human milk and thus, contribute to the lower incidence of inflammatory diseases such as necrotizing enterocolitis in breast-fed versus formula-fed infants.

Formation of platelet-leukocyte aggregates in inflammatory bowel disease

OBJECTIVES

Formation of platelet-leukocyte aggregates (PLAs) is increased in several inflammatory and thrombotic conditions. This may result from and enhance platelet and neutrophil activation and could contribute to the inflammatory process in inflammatory bowel disease (IBD). We investigated platelet-leukocyte aggregation in patients with IBD and its relation to treatment, disease activity and platelet and neutrophil activation.

METHODS

PLAs, platelet activation (P-selectin expression) and neutrophil activation (L-selectin expression) were assessed 30 and 180 minutes after drawing blood into EDTA/citrate-theophylline-adenosine and dipyridamole, a novel anticoagulant, using fluorescent antibodies to CD45 (for leukocytes), CD42a (for platelets), CD62P (P-selectin) and CD62L (L-selectin) and flow cytometry. Platelet activation was also measured using the ADVIA 120 hematology analyser.

RESULTS

Samples from 67 patients with IBD measured within 30 minutes had a higher platelet count (P < 0.001), more platelets expressing P-selectin (P = 0.01), and more PLAs (P < 0.01) than from 20 healthy controls and more PLAs (P < 0.05) than from 9 controls with inflammatory arthropathies. IBD patients on thiopurines had fewer PLAs than those not taking them (P < 0.05); corticosteroids and aminosalicylates had no such effects. Incubation for 180 minutes increased the number of platelets expressing P-selectin (P < 0.0001), and the number of PLAs (P < 0.0001). The PLAs correlated with the number of platelets expressing P-selectin before (r=+0.40, P < 0.001) and after (r=+0.66, P < 0.0001) incubation.

CONCLUSIONS

The number of PLAs is higher in patients with IBD than in healthy and inflammatory controls, but their numbers are lowered by thiopurines. Increased PLA formation may in part be due to increased platelet activation and could be pathogenic in IBD.

Obligatory role of lipid mediators in platelet-neutrophil adhesion

Platelet-neutrophil interactions play an important role in thrombotic and inflammatory responses. Although it is well known that adhesion of platelets to neutrophils requires interactions of adhesion molecules on platelets such as P-selectin, or GPIIb/IIIa with their counterparts on neutrophils, little is known on the role of lipid mediators in this response. Here we studied involvement of thromboxane (TX) A2, platelet activating factor (PAF) and cysteinyl leukotrienes (cysLTs) in the mechanisms of platelet-neutrophil adhesion that was induced by thrombin (10-100 mU/ml), fMLP (0.01-1 microM) or LPS (0.001-100 microg/ml). All three stimulators in a concentration- and time-dependent manner induced platelet-neutrophil adhesion as quantified by the method of Jungi et al. [Blood 67(3) (1986) 629]. Platelet-neutrophil adhesion induced by each of the three activators was inhibited by blocking antibodies towards P-selectin, GPIIb/IIIa or CD18, but it was not affected by anti-E selectin antibody. Moreover, platelet-neutrophil adhesion induced by thrombin, fMPL or LPS was inhibited by the inhibitor of cyclooxygenase (aspirin), by TXA2 synthase inhibitor (camonagrel), by PAF receptor antagonist (WEB 2170), by the inhibitor of FLAP (MK 886) and by cysLTs receptors antagonist (MK 571). On the other hand, the selective inhibitor of COX-2 (rofecoxib) as well as the inhibitor of cytochrome P450-dependent monoxygenase (17-ODYA) were ineffective. In summary, adhesion of platelets to neutrophils is regulated not only by specific interaction between adhesion molecules on platelets and neutrophils, but also by lipid mediators such as TXA2, PAF and cysLTs released upon activation of platelets or/and neutrophils.

Lack of influence of the COX inhibitors metamizol and diclofenac on platelet GPIIb/IIIa and P-selectin expression in vitro

Background

The effect of non-steroidal anti-inflammatory drugs (NSAIDs) for reduced platelet aggregation and thromboxane A₂ synthesis has been well documented. However, the influence on platelet function is not fully explained. Aim of this study was to examine the influence of the COX-1 inhibiting NSAIDs, diclofenac and metamizol on platelet activation and leukocyte-platelet complexes, in vitro. Surface expression of GPIIb/IIIa and P-selectin on platelets, and the percentage of platelet-leukocyte complexes were investigated.

Methods

Whole blood was incubated with three different concentrations of diclofenac and metamizol for 5 and 30 minutes, followed by activation with TRAP-6 and ADP. Rates of GPIIb/IIIa and P-selectin expression, and the percentage of platelet-leukocyte complexes were analyzed by a flow-cytometric assay.

Results

There were no significant differences in the expression of GPIIb/IIIa and P-selectin, and in the formation of platelet-leukocyte complexes after activation with ADP and TRAP-6, regarding both the time of incubation and the concentrations of diclofenac and metamizol.

Conclusions

Accordingly, the inhibitory effect of diclofenac and metamizol on platelet aggregation is not related to a reduced surface expression of P-selectin and GPIIb/IIIa on platelets.

Platelet-neutrophil conjugate formation is increased in diabetic women with cardiovascular disease

Background

More than seventeen million Americans are afflicted with diabetes and these people have four times the rate of coronary heart disease (CHD) as non-diabetics. Furthermore, diabetic women have a 3.8 fold greater risk for CHD compared to diabetic men. Little is known why diabetic women are at an increased risk for CHD. It is possible that diabetic women with cardiovascular disease (CVD) have a greater inflammatory response resulting in an increased platelet neutrophil conjugate formation than diabetic men with CVD or non-diabetic women with CVD. This study tested the hypothesis that platelet-neutrophil conjugates, which are associated with several cardiovascular diseases, are increased in diabetic women with CVD compared to diabetic men with CVD and non-diabetic women with CVD.

Methods

Platelet-neutrophil conjugates were quantified by flow cytometry. The primary method is through direct binding of the neutrophil PSGL-1 receptor with P-selectin expressed on the platelet.

Results

In this study, we found when the blood was stimulated with PAF (platelet activating factor), diabetic women without CVD demonstrated an increase in platelet-neutrophil conjugates compared to diabetic women with CVD and non-diabetic women with CVD (% conjugates: 63.3 ± 5.2 vs 46.8 ± 4.3 vs 48.6 ± 3.4, p < 0.05). The stimulation ratio was significantly increased in diabetic and non-diabetic women with CVD in comparison to diabetic men with CVD (ratio: 3.3 ± 0.4 vs 3.3 ± 0.3 vs 2.1 ± 0.3, p < 0.05).

Conclusion

These results suggest that platelets and neutrophils in diabetic women have a greater potential for activation compared to diabetic men and may contribute to thrombosis/inflammation and the greater severity of coronary heart disease observed in diabetic women as compared to diabetic men.

Platelets are essential for leukocyte recruitment in allergic inflammation

BACKGROUND

The role of platelets in inflammation is recognized but poorly characterized, and little is known of their interaction with leukocytes. However, platelet-leukocyte interactions have been demonstrated in cardiovascular disease, culminating in enhanced leukocyte recruitment.

OBJECTIVES

This study was undertaken to assess the possibility and potential role of similar phenomena occurring in asthmatic patients, a murine model of allergic inflammation, and in vitro adhesion studies.

METHODS

Asthmatic patients had blood taken at various time points to document the degree of leukocyte activation and the presence of platelet-leukocyte aggregates through FACS analysis before and after allergen exposure. Similar studies were carried out in mice exposed to allergen after previous sensitization, with some groups being selectively depleted of platelets through both an immunologic (antiplatelet antiserum) and nonimmunologic (busulfan) method. Additionally, lavage fluid and airway tissue were analyzed to assess the degree of pulmonary leukocyte recruitment. The importance of platelets on leukocyte adhesion to the endothelium was then assessed with in vitro incubation of radiolabeled leukocytes in the presence of activated platelets on cultured human vascular endothelial cells.

RESULTS

We have observed circulating platelet-leukocyte aggregates in the blood of allergic asthmatic patients during the allergen-induced late asthmatic response and in sensitized mice after allergen exposure. In platelet-depleted mice infiltration of leukocytes into airways after allergen challenge was significantly reduced and could be restored by means of infusion of platelets from allergic animals, indicating an essential role for platelets in leukocyte recruitment. CD11b expression on leukocytes involved in aggregates with platelets, although not on free leukocytes, was upregulated. Furthermore, the presence of autologous platelets augmented the adhesion of human polymorphonuclear leukocytes to cultured vascular endothelial cells, an effect that was found to be endothelial cell dependent and to involve platelet activation.

CONCLUSION

These results suggest that platelet participation in cell recruitment occurs at the level of the circulation and might involve the priming of leukocytes for subsequent adhesion and transmigration into tissues.

Platelet chemokines and chemokine receptors: linking hemostasis, inflammation, and host defense

Blood platelets play critical roles in hemostasis, providing rapid essential protection against bleeding and catalyzing the important slower formation of stable blood clots via the coagulation cascade. They are also involved in protection from infection by phagocytosis of pathogens and by secreting chemokines that attract leukocytes. Platelet function usually is activated by primary agonists such as adenosine diphosphate (ADP), thrombin, and collagen, whereas secondary agonists like adrenalin do not induce aggregation on their own but become highly effective in the presence of low levels of primary agonists. Current research has revealed that chemokines represent an important additional class of agonists capable of causing significant activation of platelet function. Early work on platelet alpha-granule proteins suggested that platelet factor 4, now known as CXCL4, modulated aggregation and secretion induced by low agonist levels. Subsequent reports revealed the presence in platelets of messenger RNA for several additional chemokines and chemokine receptors. Three chemokines in particular, CXCL12 (SDF-1), CCL17 (TARC), and CCL22 (MDC), recently have been shown to be strong and rapid activators of platelet aggregation and adhesion after their binding to platelet CXCR4 or CCR4, when acting in combination with low levels of primary agonists. CXCL12 can be secreted by endothelial cells and is present in atherosclerotic plaques, whereas CCL17 and CCL22 are secreted by monocytes and macrophages. Platelet activation leads to the release of alpha-granule chemokines, including CCL3 (MIP-1alpha), CCL5 (RANTES), CCL7 (MCP-3), CCL17, CXCL1 (growth-regulated oncogene-alpha), CXCL5 (ENA-78), and CXCL8 (IL-8), which attract leukocytes and further activate other platelets. These findings help to provide a direct linkage between hemostasis, infection, and inflammation and the development of atherosclerosis.

Severe meningococcal disease is characterized by early neutrophil but not platelet activation and increased formation and consumption of platelet-neutrophil complexes

Approximately 25% of polymorphonuclear leukocytes (PMNL) circulate in heterotypic complexes with one or more activated platelets. These platelet-neutrophil complexes (PNC) require platelet CD62P expression for their formation and represent activated subpopulations of both cell types. In this study, we have investigated the presence, time course, and mechanisms of PNC formation in 32 cases of severe pediatric meningococcal disease (MD) requiring intensive care. There were marked early increases in PMNL CD11b/CD18 expression and activation, and reduced CD62L expression compared with intensive care unit control cases. Minimal platelet expression of the active form of alphaIIbbeta3 (GpIIb/IIIa) was seen. PNC were reduced on presentation and fell to very low levels after 24 h. Immunostaining of skin biopsies demonstrated that PNC appear outside the circulation in MD. In vitro studies of anticoagulated whole blood inoculated with Neisseria meningitidis supported these clinical findings with marked increases in PMNL CD11b/CD18 expression and activation but no detectable changes in platelet-activated alphaIIbbeta3 or CD62P expression. In vitro PMNL activation with N. meningitidis (or other agonists) potentiated the formation of PNC in response to platelet activation with adenine diphosphate. Therefore, in severe MD, PMNL activation is likely to promote PNC formation, and we suggest that the reduced levels of PNC seen in established MD reflect rapid loss of PNC from the circulation rather than reduced formation.

Platelets abrogate leukotriene B(4) generation by human blood neutrophils stimulated with monosodium urate monohydrate or f-Met-Leu-Phe in vitro

Neutrophils are physiologically associated with platelets in whole blood. Inflammatory reactions can be modulated by the presence of platelets. To investigate the influence of platelets on neutrophil activity, we studied the 5-lipoxygenase (5-LOX) metabolic pathway in normal human blood neutrophils stimulated with f-Met-Leu-Phe (fMLP) or monosodium urate monohydrate (MSUM) in the presence of autologous platelets. Platelets inhibited by more than 90% the synthesis of leukotriene B(4) and 5-HETE in neutrophils activated with fMLP or MSUM. The addition of exogenous arachidonic acid did not reverse the inhibitory effect of platelets on 5-LOX-generated metabolites in fMLP- or MSUM-activated neutrophils. Preincubation of neutrophils with adenosine deaminase reversed the inhibitory effect of platelets in fMLP-treated neutrophils, indicating that adenosine was responsible for the platelet inhibition of leukotriene B(4) and 5-HETE formation. In contrast, adenosine deaminase had no influence on the inhibitory effects of platelets in MSUM-stimulated cells. These results suggest that platelets can inhibit the synthesis of 5-LOX products (a). by acting mainly downstream to phospholipase A(2) in cells stimulated by fMLP or MSUM, (b). through adenosine when neutrophils are activated with fMLP, and (c). by an adenosine-independent mechanism in MSUM-activated neutrophils by an as-yet-unidentified mediator.

Platelet satellitism, spurious neutropenia, and cutaneous vasculitis: casual or causal association?

About 90 cases of platelet satellitism (PS) have been published, most of them involving neutrophils, a few comprising monocytes, and one case involving basophils. The case of a 30-year-old female patient with cutaneous vasculitis who developed asymptomatic severe neutropenia is reported. All blood smears (BS) prepared from peripheral blood samples collected with either ethylenediaminetetraacetic acid, trisodium citrate, and heparin showed PS involving neutrophils, eosinophils, and monocytes. Immunohistochemistry analysis of her skin biopsy and BS, employing peroxidase stain for the detection of antibodies directed against IgG, IgA, IgM, and C3, revealed an intense positive reaction only for IgG in the endothelium and leukocyte clumps within the microvasculature, as well as in peripheral blood neutrophils displaying the PS phenomenon. Transfer of the PS phenomenon was demonstrated by incubating the patient's plasma with leukocytes from an ABO-compatible healthy donor. In our patient, PS did not disappear after incubation at 37 degrees C, suggesting that this might be a different or "atypical" PS phenomenon probably mediated by an autoimmune process involving an IgG-class antibody responsible for both conditions, PS, and cutaneous vasculitis.

Immunomodulatory effects of breast milk oligosaccharides

Breast milk oligosaccharides are excreted in urine in amounts that suggest that they may exist in the circulation at levels compatible with a physiological function. Some oligosaccharides have structural similarity to cellular adhesion molecules and may influence adhesion of cells in breast fed infants. In this study, breast milk oligosaccharides were purified and incubated in assays of cell adhesion. They were found to inhibit neutrophil adhesion to stimulated vascular endothelial cells in a dose dependent fashion. In contrast they enhanced platelet-neutrophil complex formation. These results indicate that breast milk oligosaccharides may play a physiological role in modulating cellular adhesion in vivo.

Are leukocytes in salvaged washed autologous blood harmful for the recipient? The results of a pilot study

To explore whether polymorphonuclear leukocytes (PMNL) are activated to the priming threshold through intraoperative blood salvage, and are thus able to induce endothelial damage, we investigated chemotactic response (n = 20) and respiratory burst (RB; n = 20) of PMNL without (basal respiratory burst, bPMNL-RB) and after in vitro stimulation with formyl-Met-Leu-Phe (fMLP-RB) and phorbol myristate acetate (PMA-RB). Blood was processed with a continuous autotransfusion device (CATS). Heparin (Heparin group) and sodium citrate (Citrate group) were used alternately as an anticoagulant for each half of the chemotaxis and RB studies. Comparison of measurements from the processed autologous erythrocyte concentrates (paEC) to pre- and intraoperative arterial blood samples showed no statistically significant difference for any test of PMNL functional responses in an orthopedic patient population. Analysis of intraindividual changes demonstrated a significantly increased bPMNL-RB (both groups, P = 0.0032; Heparin group, P = 0.0098), fMLP-RB (both groups, P = 0.0484; Citrate group, P = 0.0371), and PMA-RB (Citrate group, P = 0.002) in the paEC compared with intraoperative arterial samples, whereas the chemotactic response did not change. Nevertheless, median values of all RB measurements in the paEC were within the range of pre- and intraoperative values, indicating that PMNLs contained in the paEC are neither impaired nor activated to the priming threshold. The results confirm the clinical experience that intraoperative blood salvage is safe to use during major orthopedic surgery and questions the beneficial effect of special leukocyte-removing filters.

Increased circulating platelet-leukocyte aggregates in myeloproliferative disorders is correlated to previous thrombosis, platelet activation and platelet count

Platelet-leukocyte adhesion may occur as a consequence of platelet activation and possibly plays a key role in the deposition of activated platelets and fibrin in the thrombotic plug. The aim of the present study was to assess by whole blood flow cytometry the presence of circulating platelet-leukocyte aggregates (PLA) and the platelet-leukocyte response to platelet agonist stimulation (ADP and TRAP) in 50 patients with chronic myeloproliferative disorders (MPD) and 30 controls. PLA were identified as platelet-granulocyte/monocyte aggregates (PGMA), platelet-monocyte aggregates (PMA) and defined as the percentage of leukocytes coexpressing the platelet-specific marker glycoprotein Ib. Compared to controls the mean percentage of PGMA and PMA was increased in unstimulated whole blood from patients with MPD (7.98 vs. 1.76%; p<0.001 and 12.34 vs. 3.2%; p<0.001, respectively). The percentage of PGMA was correlated to the platelet count (r=0.46; p<0.001), percentage of P-selectin (r=0.69; p<0.001) and thrombospondin (r=0.58; p<0.001) positive platelets and platelet expression of GPIV (r=0.33; p=0.02). The mean percentage of PGMA and PMA was significantly increased in ADP-stimulated whole blood of patients (57.14 vs. 47.92%; p=0.009 and 54.91 vs. 45.89%; p<0.001, respectively). Compared to patients without a history of thrombosis, patients having experienced microvascular disturbances or a thrombotic event had a higher mean percentage of PGMA and PMA in non-stimulated whole blood (10.07 vs. 6.34%; p=0.025 and 14.81 vs. 10.48%; p=0.021, respectively) and a higher percentage of PGMA in ADP stimulated whole blood (64.32 vs. 51.50%; p<0.01). These data document an increased frequency of PLA in non-stimulated whole blood in MPD associated with a previous history of thrombosis or microvascular disturbances.

Oligosaccharides in human milk: structural, functional, and metabolic aspects

Research on human milk oligosaccharides (HMOs) has received much attention in recent years. However, it started about a century ago with the observation that oligosaccharides might be growth factors for a so-called bifidus flora in breast-fed infants and extends to the recent finding of cell adhesion molecules in human milk. The latter are involved in inflammatory events recognizing carbohydrate sequences that also can be found in human milk. The similarities between epithelial cell surface carbohydrates and oligosaccharides in human milk strengthen the idea that specific interactions of those oligosaccharides with pathogenic microorganisms do occur preventing the attachment of microbes to epithelial cells. HMOs may act as soluble receptors for different pathogens, thus increasing the resistance of breast-fed infants. However, we need to know more about the metabolism of oligosaccharides in the gastrointestinal tract. How far are oligosaccharides degraded by intestinal enzymes and does oligosaccharide processing (e.g. degradation, synthesis, and elongation of core structures) occur in intestinal epithelial cells? Further research on HMOs is certainly needed to increase our knowledge of infant nutrition as it is affected by complex oligosaccharides.

Platelet and leucocyte activation in childhood sickle cell disease: association with nocturnal hypoxaemia

We hypothesized that vaso-occlusive events in childhood sickle cell disease (SCD) may relate to inflammatory cell activation as well as interactions between sickle erythrocytes and vascular endothelium. Peripheral blood was examined from 24 children with SCD, of whom 12 had neurological sequelae and seven had frequent painful crises, and 10 control subjects. Platelet (CD62P and CD40L expression) and granulocyte (CD11b expression) activation and levels of platelet-erythrocyte and platelet-granulocyte complexes were determined by flow cytometry. Platelets (P = 0.019), neutrophils (P = 0.02) and monocytes (P = 0.001) were more activated and there were increased platelet-erythrocyte complexes (P = 0.026) in SCD patients compared with controls. Platelet-granulocyte complexes were not raised. There were no differences between the different groups of SCD. As hypoxia activates monocytes, platelets and endothelial cells and causes sickling of SCD erythrocytes, we also investigated 20 SCD patients with overnight pulse oximetry. Minimum overnight saturation correlated with the level of platelet-erythrocyte complexes (Spearman's rho -0.668, P < 0.02), neutrophil CD11b (Spearman's rho -0.466, P = 0.038) and monocyte CD11b (Spearman's rho -0.652, P = 0. 002). These findings provide important clues about the mechanism by which SCD patients may become predisposed to vaso-occlusive events.

Heparin, platelet aggregation, neutrophils, and cardiopulmonary bypass

Cardiopulmonary bypass (CPB) is associated with both neutrophil activation and failure of platelets to form large stable aggregates. We aimed to determine the effects of heparin and of neutrophil activation on platelet aggregation in whole blood. Fourteen patients undergoing routine aortocoronary bypass grafting and NSAID-free for over 7 days were studied before and after heparinisation, and at end-CPB. Whole blood, anticoagulated with rHirudin, was stirred for 3 minutes, and macroaggregation in response to collagen (0.6 microg. mL(-1)) or the neutrophil stimulant fMLP (10(-7)M) was determined by whole blood impedance aggregometry. Microaggregation was measured by counting unaggregated single platelets (corrected for haemodilution). The blood of volunteers was studied in vitro.

PATIENTS

Before CPB, heparin effectively abolished platelet macroaggregation induced by collagen (20.5 to 1.4 Ohms) or fMLP (3.9 to 0 Ohms (p<0.0001). CPB had no additional effect. Heparinisation also reduced the platelet count from 127 (110-170) to 95 (64-117). The inhibition of macroaggregation could not be reversed by ex vivo heparinase.

VOLUNTEERS

In vitro, the same heparin concentration, as measured in vivo (4 micromL(-1)), inhibited collagen-induced macroaggregation (20.3 to 14.7 Omega), but this effect was less than that observed ex vivo and was reversed by heparinase. In vitro heparin promoted fMLP macroaggregation (2.9 to 8.6 Omega). The inhibition of macroaggregation resulted from heparinisation, per se, rather than CPB and was insensitive to heparinase. There was less inhibition by in vitro heparin, which was reversible by heparinase, indicating a direct effect of heparin in vitro. The disparate findings are suggestive of an indirect action by heparin in vivo on macroaggregation, although heparin had a small direct stimulatory action on microaggregation.

The preanalytic phase. An important component of laboratory medicine

The preanalytic phase is an important component of total laboratory quality. A wide range of variables that affect the result for a patient from whom a specimen of blood or body fluid has been collected, including the procedure for collection, handling, and processing before analysis, constitute the preanalytic phase. Physiologic variables, such as lifestyle, age, and sex, and conditions such as pregnancy and menstruation, are some of the preanalytic phase factors. Endogenous variables such as drugs or circulating antibodies might interact with a specific method to yield spurious analytic results. The preanalytic phase variables affect a wide range of laboratory disciplines.

The use of flow cytometry to measure neutrophil function

Neutrophils are important professional phagocytic cells that provide the host with a first line of defense against acute bacterial and fungal diseases and recurrent, severe or unusual infections are associated with inherited defects of neutrophil function. Furthermore, abundant evidence links inappropriate neutrophil-mediated tissue damage to the pathogenesis of conditions such as acute respiratory distress syndrome, septicemia with multiorgan failure, ischemia-reperfusion injury and rheumatoid arthritis. Flow cytometry has been increasingly used to evaluate the functional capabilities of neutrophils. In this review, we discuss the use of flow cytometry to assess neutrophil functional responses including calcium mobilization, F-actin assembly, adhesion, aggregation, degranulation, phagocytosis and reactive oxygen species (ROS) production. The use of flow cytometry to identify neutrophil priming is also discussed. The advantage of flow cytometry is that the majority of neutrophil functions can be measured using a small volume of whole blood that reduces artifactual changes in function caused by purification procedures. The advent of numerous new fluorochromes and multiparametric analysis allows the simultaneous measurement of several neutrophil functions in the same population of cells. Flow cytometric analysis provides a rapid screen for abnormalities of neutrophil function and reflects more accurately their behavior in vivo.

Functional expression of transmembrane 4 superfamily molecules on human eosinophils

BACKGROUND

Transmembrane 4 superfamily (TM4SF) molecules are exclusively found on hematopoietic cells. Several members of the TM4SF are reported to be associated with other cell surface molecules, including integrins, and might participate in signal transduction, but little is known about their role on eosinophils. In the present study, we determined the expression and function of TM4SF molecules on human eosinophils.

METHODS

Surface expression of TM4SF molecules on purified peripheral blood eosinophils was examined using indirect immunofluorescence and flow cytometry. Purified eosinophils were incubated with anti-TM4SF monoclonal antibodies (mAbs) for up to 24 h. Eosinophil activation was evaluated by measuring eosinophil homotypic aggregation as well as changes in surface expression of CD11b or CD62L by flow cytometry.

RESULTS

Freshly isolated eosinophils expressed CD9, CD37, CD53, CD63 and CD81. Incubation with anti-CD9 mAb but not with anti-CD37, CD53, CD63 or CD81 mAb induced significant eosinophil homotypic aggregation. Incubation with any of the anti-TM4SF mAb for 30 min failed to alter the expression of either CD11b or CD62L on eosinophils. In contrast, the expression of CD11b was significantly enhanced after 24 h of incubation with anti-CD53 mAb, while the expression of CD62L was significantly reduced with anti-CD81 mAb.

CONCLUSIONS

Cross-linking of some surface TM4SF molecules induced significant eosinophil homotypic aggregation, upregulation of CD11b expression, or CD62L shedding, consistent with activation of eosinophils. Our data suggest that several TM4SF molecules are functionally expressed on human eosinophils, and therefore might participate in allergic inflammation.

Circulating platelet-neutrophil complexes represent a subpopulation of activated neutrophils primed for adhesion, phagocytosis and intracellular killing

Platelets play a prominent role in linking the processes of inflammation, haemostasis and thrombosis. Recent studies have shown that platelets form heterotypic aggregates with leucocytes via platelet CD62P and leucocyte beta2 integrins. These interactions have been observed in vitro in blood taken from healthy volunteers and in clinical conditions in which thrombosis and inflammation are prominent. This study investigated the properties of platelet-neutrophil complexes (PNCs) in anticoagulated whole blood. At rest, neutrophils in PNCs exhibit a significantly more activated adhesion molecule profile than free neutrophils with increased CD11b expression and activation (increased binding of the CD11b/CD18 'activation reporter' monoclonal antibody 24) and decreased CD62L expression. In addition, neutrophils in PNCs phagocytosed significantly more Neisseria meningitidis and produced more toxic oxygen metabolites than free neutrophils. Stimulation with the platelet agonist adenosine diphosphate (ADP) led to further increases in CD11b expression and activation, loss of CD62L as well as increased phagocytosis and toxic oxygen metabolite production throughout the whole neutrophil population. When these experiments were repeated with the CD62P blocking antibody G1 the effects were inhibited to a variable extent, dependent upon the parameter under investigation. These results indicate that both soluble and contact-dependent factors contribute to platelet-mediated neutrophil activation. Platelet neutrophil complexes represent a large subpopulation of neutrophils with a more activated adhesion molecule profile, and a greater capacity for phagocytosis and toxic oxygen metabolite production. This study provides further support for a role for PNCs in both health and disease.