Interaction with autologous platelets multiplies interleukin-1 and tumor necrosis factor production in mononuclear cells

Platelet transfusions in a murine model of neonatal polymicrobial sepsis: Divergent effects on inflammation and mortality

BACKGROUND

Platelet transfusions (PTxs) are often given to septic preterm neonates at high platelet count thresholds in an attempt to reduce bleeding risk. However, the largest randomized controlled trial (RCT) of neonatal transfusion thresholds found higher mortality and/or major bleeding in infants transfused at higher thresholds. Using a murine model, we investigated the effects of adult PTx on neonatal sepsis-induced mortality, systemic inflammation, and platelet consumption.

STUDY DESIGN AND METHODS

Polymicrobial sepsis was induced via intraperitoneal injection of cecal slurry preparations (CS1, 2, 3) into P10 pups. Two hours after infection, pups were transfused with washed adult Green Flourescent Protein (GFP+) platelets or control. Weights, platelet counts, and GFP% were measured before 4 and 24 h post-infection. At 24 h, blood was collected for quantification of plasma cytokines.

RESULTS

The CS batches varied in 24 h mortality (11%, 73%, and 30% in CS1, 2, and 3, respectively), due to differences in bacterial composition. PTx had differential effects on sepsis-induced mortality and systemic inflammatory cytokines, increasing both in mice infected with CS1 (low mortality) and decreasing both in mice infected with CS2 and 3. In a mathematical model of platelet kinetics, the consumption of transfused adult platelets was higher than that of endogenous neonatal platelets, regardless of CS batch.

DISCUSSION

Our findings support the hypothesis that transfused adult platelets are consumed faster than endogenous neonatal platelets in sepsis and demonstrate that PTx can enhance or attenuate neonatal inflammation and mortality in a model of murine polymicrobial sepsis, depending on the composition of the inoculum and/or the severity of sepsis.

Monocytes complexed to platelets differentiate into functionally deficient dendritic cells

In addition to their role in hemostasis, platelets store numerous immunoregulatory molecules such as CD40L, TGFβ, β2-microglobulin, and IL-1β and release them upon activation. Previous studies indicate that activated platelets form transient complexes with monocytes, especially in HIV infected individuals and induce a proinflammatory monocyte phenotype. Because monocytes can act as precursors of dendritic cells (DCs) during infection/inflammation as well as for generation of DC-based vaccine therapies, we evaluated the impact of activated platelets on monocyte differentiation into DCs. We observed that in vitro cultured DCs derived from platelet-monocyte complexes (PMCs) exhibit reduced levels of molecules critical to DC function (CD206, dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin, CD80, CD86, CCR7) and reduced antigen uptake capacity. DCs derived from PMCs also showed reduced ability to activate naïve CD4+ and CD8+ T cells, and secrete IL-12p70 in response to CD40L stimulation, resulting in decreased ability to promote type-1 immune responses to HIV antigens. Our results indicate that formation of complexes with activated platelets can suppress the development of functional DCs from such monocytes. Disruption of PMCs in vivo via antiplatelet drugs such as Clopidogrel/Prasugrel or the application of platelet-free monocytes for DCs generation in vitro, may be used to enhance immunization and augment the immune control of HIV.

Using Dendritic Cell-Based Immunotherapy to Treat HIV: How Can This Strategy be Improved?

Harnessing dendritic cells (DC) to treat HIV infection is considered a key strategy to improve anti-HIV treatment and promote the discovery of functional or sterilizing cures. Although this strategy represents a promising approach, the results of currently published trials suggest that opportunities to optimize its performance still exist. In addition to the genetic and clinical characteristics of patients, the efficacy of DC-based immunotherapy depends on the quality of the vaccine product, which is composed of precursor-derived DC and an antigen for pulsing. Here, we focus on some factors that can interfere with vaccine production and should thus be considered to improve DC-based immunotherapy for HIV infection.

The role of platelet MyD88 in host response during gram-negative sepsis

BACKGROUND

Beside their role in hemostasis, platelets serve as sentinel cells in host defense during infection. In sepsis, platelets have been implicated in both beneficial (antibacterial) and detrimental responses (thrombosis and organ damage). Toll-like receptors and their common adaptor, myeloid differentiation factor 88 (MyD88), are essential for pathogen recognition and protective immunity. Platelets express functional Toll-like receptors and MyD88, which participate in platelet responsiveness to bacterial agonists.

OBJECTIVE

Considering the pivotal involvement of platelets and MyD88 in the host response to bacteria, we studied the role of platelet MyD88 in gram-negative sepsis using intravenous and airway infections with the common human sepsis pathogen Klebsiella pneumoniae.

METHODS

Platelet-specific Myd88(-/-) mice were generated by crossing mice with a conditional Myd88 flox allele with mice expressing Cre recombinase controlled by the platelet factor 4 promoter. In a reverse approach, full Myd88(-/-) mice were transfused with wild-type platelets.

RESULTS

In both settings, platelet MyD88 did not impact on bacterial growth or dissemination. In addition, platelet MyD88 did not influence hallmark sepsis responses such as thrombocytopenia, coagulation or endothelial activation, or distant organ injury. Platelet MyD88 played no role in lung pathology during pneumonia-derived sepsis.

CONCLUSION

Despite known literature, platelet MyD88-dependent TLR signaling does not contribute to the host response during gram-negative sepsis.

Thrombocytopenia impairs host defense in gram-negative pneumonia-derived sepsis in mice

Thrombocytopenia is a common finding in sepsis and associated with a worse outcome. We used a mouse model of pneumonia-derived sepsis caused by the human pathogen Klebsiella pneumoniae to study the role of platelets in host response to sepsis. Platelet counts (PCs) were reduced to less than a median of 5 × 10(9)/L or to 5 to 13 × 10(9)/L by administration of a depleting antibody in mice infected with Klebsiella via the airways. Thrombocytopenia was associated with strongly impaired survival during pneumonia-derived sepsis proportional to the extent of platelet depletion. Thrombocytopenic mice demonstrated PC-dependent enhanced bacterial growth in lungs, blood, and distant organs. Severe thrombocytopenia resulted in hemorrhage at the primary site of infection, but not in distant organs. PCs of 5 to 13 × 10(9)/L were sufficient to largely maintain hemostasis in infected lungs. Thrombocytopenia did not influence lung inflammation or neutrophil recruitment and did not attenuate local or systemic activation of coagulation or the vascular endothelium. PCs <5 × 10(9)/L even resulted in enhanced coagulation and endothelial cell activation, which coincided with increased proinflammatory cytokine levels. In accordance, low PCs in whole blood enhanced Klebsiella-induced cytokine release in vitro. These data suggest that platelets play an important role in host defense to Klebsiella pneumosepsis.

Platelets protect from septic shock by inhibiting macrophage-dependent inflammation via the cyclooxygenase 1 signalling pathway

Although it has long been known that patients with sepsis often have thrombocytopenia and that septic patients with severe thrombocytopenia have a poor prognosis and higher mortality, the role of platelets in the pathogenesis of sepsis is poorly understood. Here we report a protective role of platelets in septic shock. We show that experimental thrombocytopenia induced by intraperitoneal injection of an anti-glycoprotein Ibα monoclonal antibody increases mortality and aggravates organ failure, whereas transfusion of platelets reduces mortality in lipopolysaccharide-induced endotoxemia and a bacterial infusion mouse sepsis model. Plasma concentrations of proinflammatory cytokines TNF-α and IL-6 are elevated by thrombocytopenia and decreased by platelet transfusion in septic mice. Furthermore, we identify that platelets protect from septic shock by inhibiting macrophage-dependent inflammation via the COX1/PGE₂/EP4-dependent pathway. Thus, these findings demonstrate a previously unappreciated role for platelets in septic shock and suggest that platelet transfusion may be effective in treating severely septic patients.

Antithrombin reduces monocyte and neutrophil CD11b up regulation in addition to blocking platelet activation during extracorporeal circulation

BACKGROUND

Patients undergoing cardiac surgery requiring cardiopulmonary bypass develop a systemic inflammatory reaction. Antithrombin III (AT) has anticoagulant effects but also shows evidence of anti-inflammatory activity. The aim of this study was to examine whether exogenous AT could reduce white blood cell activation (CD11b up regulation or elastase release), in addition to inhibiting platelet (PLT) activation and fibrin generation, during simulated cardiopulmonary bypass (sCPB), undertaken in the absence of endothelium.

STUDY DESIGN AND METHODS

sCPB was carried out with minimally heparinized (2 U/mL) human blood for 90 minutes in controls and with supplementation by low-dose (1 U/mL) and high-dose (5 U/mL) AT.

RESULTS

High-dose AT blunted thrombin generation during sCPB (prothrombin fragment 1.2); both doses significantly inhibited thrombin activity (fibrinopeptide A). Complement activation (C3a and C5b-9) was unaffected by AT. High-dose AT inhibited PLT activation (P-selectin expression and P-selectin-dependent monocyte-PLT conjugate formation). AT supplementation at the higher dose significantly abrogated monocyte and neutrophil CD11b up regulation and neutrophil elastase release.

CONCLUSION

In addition to anticoagulant and anti-PLT effects, pharmacologic AT doses significantly blunted monocyte and neutrophil CD11b up regulation and neutrophil elastase release during sCPB, independent of endothelial effects. These data provide evidence for the direct anti-inflammatory activity of AT that has clinical relevance for CPB complications.

Phosphodiesterase III Inhibition Affects Platelet-Monocyte Aggregate Formation Depending on the Axis of Stimulation

OBJECTIVE

The purpose of this study was to investigate the effect of the phosphodiesterase (PDE) type 3 inhibitor milrinone on the adhesion of platelets to monocytes in vitro.

DESIGN

Prospective study.

SETTING

University experimental laboratory.

PARTICIPANTS

Ten healthy volunteers.

INTERVENTIONS

Whole blood was incubated with 1, 10, or 100 micromol/L of milrinone. After stimulation with N-formyl-methionyl-leucyl-phenylalanine (FMLP) or adenosine-5-diphosphate (ADP), platelet-monocyte adhesion and CD11b, PSGL-1, GPIIb/IIIa, and P-selectin expression were measured by flow cytometry.

MEASUREMENTS AND RESULTS

The formation of platelet-monocyte conjugates after PDE3 inhibition depended on the type of stimulation. In unstimulated and FMLP-stimulated blood platelet monocytes, aggregation was enhanced by increasing concentrations of milrinone. This augmentation was accompanied by a rise in P-selectin expression in platelets. In ADP-stimulated blood the number of platelet-monocyte aggregates decreased with increasing concentrations of milrinone. Concurrent with the reported antiinflammatory properties of PDE-inhibition, an inhibition of CD11b expression was found in monocytes after stimulation with FMLP. In contrast, in unstimulated samples lower concentrations of milrinone caused an increase in CD11b.

CONCLUSIONS

These findings suggest that the effects of PDE3 inhibition on platelets and monocytes are modified by the type of stimulation and only partially suppress the inflammatory response of platelets and monocytes. The increase in platelet-monocyte conjugates in unstimulated and FMLP-stimulated blood suggested that PDE3 inhibition may also trigger proinflammatory reactions.

Detection of human P2X7 nucleotide receptor polymorphisms by a novel monocyte pore assay predictive of alterations in lipopolysaccharide-induced cytokine production

The nucleotide receptor P2X(7) is expressed by most leukocytes and initiates signaling events that amplify numerous LPS responses. We tested the hypothesis that loss-of-function polymorphisms in the human P2X(7) gene predispose to the production of an anti-inflammatory mediator balance. Accordingly, we developed a novel P2X(7) pore assay in whole blood that magnifies the activity from wild-type alleles and preserves the gene dosage effect for the 1513 C polymorphism (AA, 69 +/- 4; AC, 42 +/- 4; and CC, 6 +/- 1-fold stimulation). Thirty of 200 healthy individuals were identified as having low P2X(7) pore activity. Seven low pore subjects were 1513 CC, 3 and 11 participants had the other known variants 946 GA and 1729 TA respectively; the remaining 9 volunteers likely have novel polymorphisms. Because platelets are a large source of extracellular ATP during inflammation, whole blood was treated ex vivo with Salmonella typhimurium LPS in the absence of exogenous nucleotides. LPS-stimulated whole blood from individuals in the low pore activity group generated reduced plasma levels of TNF-alpha (p = 0.036) and higher amounts of IL-10 (p < 0.001) relative to the high pore controls. This reduction in the TNF-alpha to IL-10 ratio persisted to at least 24 h and is further decreased by cotreatment with 2-methylthio-ATP. The ability of P2X(7) polymorphisms to regulate the LPS-induced TNF-alpha to IL-10 ratio suggests that 15% of healthy adults may exhibit anti-inflammatory mediator responses during major infectious perturbations of the immune system, which can be predicted by P2X(7) pore activity.

The influence of platelets on the promotion of invasion by tumor cells and inhibition by antiplatelet agents

OBJECTIVE

Using a chemoinvasion assay, we show that platelets promote invasiveness of 5 pancreatic adenocarcinoma cell lines.

METHODS

Gelatin zymography and Western blot analysis were performed to detect metalloproteinase-9 (MMP-9) secreted from tumor cells in the presence or absence of platelets. The effects of antiplatelet agents on the invasiveness of tumor cells and the secretion level of MMP-9 were evaluated.

RESULTS

The number of traversed tumor cells significantly increased when incubated with platelets compared without platelets in all cell lines. The MMP-9 band was detected in all tumor cell lines, and the intensity was obviously greater in conditions of incubation with platelets than without. In the experiment of antiplatelet agents effects, it was confirmed that invasiveness of tumor cells significantly decreased following incubation with cilostazol depending on the concentration in spite of the presence of platelets. The level of MMP-9 also significantly decreased in the ELISA analysis.

CONCLUSIONS

These data mean platelets activate invasiveness of tumor cells because of enhanced MMP-9 secretion. Furthermore, anti-platelet drugs may inhibit invasiveness of tumor cells due to decreased MMP-9 secretion, and this inhibition may lead to the suppression of tumor cell invasion. We propose that antiplatelet agents are applicable in clinical treatment to inhibit metastasis of malignant tumor cells.

Comparison of two apheresis systems for the collection of CD14+ cells intended to be used in dendritic cell culture

BACKGROUND

Monocytes collected by leukapheresis are increasingly used for dendritic cell (DC) culture in cell factories suitable for DC vaccination in cancer.

STUDY DESIGN AND METHODS

Using modified MNC programs on two apheresis systems (Cobe Spectra and Fresenius AS.TEC204), leukapheresis components collected from 84 patients with metastatic malignant melanoma and from 31 healthy male donors were investigated. MNCs, monocytes, RBCs, and platelets (PLTs) in donors and components were analyzed by cell counters, WBC differential counts, and flow cytometry.

RESULTS

In 5-L collections, Astec showed better results regarding monocyte collection rates (11.0 vs. 7.4 x 10(6)/min, p = 0.04) and efficiencies (collection efficiency, 51.9 vs. 31.9%; p < 0.001). Both devices resulted in monocyte yields at an average of 1 x 10(9) (donors) and 2.5 x 10(9) (patients), whereas Astec components contained high residual RBCs. Compared to components with low residual PLTs, high PLT concentration resulted in higher monocyte loss (48 vs. 20%, p < 0.0001) before DC culture.

CONCLUSION

The Astec is more efficient in 5-L MNC collections compared to the Spectra. Components with high residual PLTs result in high MNC loss by purification procedures. Thus, optimizing MNC programs is essential to obtain components with high MNC yields and low residual cells as prerequisite for high DC yields.

Oxidative stress in septic shock and disseminated intravascular coagulation

Oxidative stress results from an oxidant/antioxidant imbalance, an excess of oxidants and/or a depletion of antioxidants. A considerable body of recent evidence suggests that oxidant stress plays a major role in several aspects of septic shock and disseminated intravascular coagulation (DIC), and it is the subject of this review. Immunohistochemical and biochemical evidence demonstrate the significant role of reactive oxygen species (ROS) in endotoxic and hemorrhagic shock, and in endothelial injury associated with DIC syndrome. Initiation of lipid peroxidation, direct inhibition of mitochondrial respiratory chain enzymes, inactivation of glyceraldehyde-3-phosphate dehydrogenase, inhibition of membrane Na+/K+ ATP-ase activity, inactivation of membrane sodium channels, and other oxidative protein modifications contribute to the cytotoxic effect of ROS. In addition, reactive oxygen species are potent triggers of DNA strand breakage, with subsequent activation of the nuclear enzyme poly-ADP ribosyl synthetase, with eventual severe energy depletion of the cells. Pharmacological evidence suggests that the peroxynitrite-poly-ADP ribosyl synthetase pathway contributes to the cellular injury in shock and endothelial injury. Treatment with superoxide dismutase mimetics (SODms), which selectively mimic the catalytic activity of the human superoxide dismutase enzymes, have been shown to prevent in vivo shock and the cellular energetic failure associated with shock.

Human platelets express heat shock protein receptors and regulate dendritic cell maturation

Immunizations using the endoplasmic reticulum-resident heat shock protein Gp96 induce specific immune responses. Specificity is based on the major histocompatibility complex class I-restricted cross-presentation of Gp96-associated peptides derived from endogenous proteins. Initiation of the immune response depends on the ability of Gp96 to induce the production of proinflammatory cytokines by macrophages and dendritic cells (DCs) and of their maturation in a fashion presumably independent of associated peptide. Both events are mediated by Gp96 receptors on antigen-presenting cells. It is known that Gp96 is released from cells at necrosis induced, for example, by virus infection. Although this event supports the efficient induction of immune responses, it might also interfere with processes that are susceptible to chronic inflammation, such as wound healing after tissue damage. Therefore, Gp96-mediated stimulation of the immune system requires tight regulation. Here we show that human thrombocytes specifically interact with Gp96 and that binding of Gp96 to platelets is enhanced more than 10-fold on activation by thrombin. Gp96 interferes with neither thrombin-induced platelet activation nor platelet aggregation. However, the presence of platelets during Gp96-mediated DC activation reduces the secretion of proinflammatory cytokines and the activation of DCs. This effect is independent of soluble platelet factors and cell-to-cell contact between DCs and thrombocytes. Thus, we provide evidence for a regulatory mechanism that neutralizes Gp96 molecules systemically, especially in the blood. This effect might be of significance in wounds in which chronic inflammation and immune responses against autoantigens have to be prevented.

Collection of autologous monocytes for dendritic cell vaccination therapy in metastatic melanoma patients

BACKGROUND

Dendritic cells (DCs) for immunotherapy of malignant melanoma can be generated from partially enriched monocytes prepared from PBMNCs. The feasibility of a single steady-state leukapheresis procedure to enrich monocytes for a complete vaccination series with up to 10 vaccinations was investigated.

STUDY DESIGN AND METHODS

Thirty-eight patients (27 males and 11 females) with metastatic melanoma were enrolled in the study. All leukapheresis procedures were performed by a continuous flow method (Spectra, Cobe BCT) with a standard MNC program.

RESULTS

An average of 11.7 L (range, 8-14 L) of whole blood was processed within 197.3 +/- 23.7 minutes, and a mean of 13.5 +/- 5.7 x 109 WBCs in a final volume of 191.0 +/- 24.2 mL was collected. The MNC purity in the apheresis component was 81.5 +/- 15.1 percent, from which 29.8 +/- 14.7 percent were monocytes. Thus, 11.0 +/- 5.0 x 109 MNCs and 3.2 +/- 2.0 x 109 monocytes were collected per procedure. Linear regression analysis revealed a high correlation between the absolute number of monocytes in peripheral blood before the apheresis procedure and the number of monocytes in the collected component (r=0.74, p < 0.0001). For the generation of DCs, 1.6 +/- 0.8 x 109 MNCs were plated into culture dishes; 3.2 +/- 1.8 percent of the cultured cells matured to DCs, which resulted in 56.5 +/- 49.4 x 106 DCs (range, 6.3-178) per patient for the complete vaccination series.

CONCLUSION

A target dose of monocytes for the complete vaccination series could be obtained by a single convenient, safe, steady-state leukapheresis procedure in each patient without the need for G-CSF mobilization. The absolute number of monocytes in peripheral blood before the apheresis procedure is the best predictive variable for the yield of monocytes in the apheresis component.

High-shear-stress-induced activation of platelets and microparticles enhances expression of cell adhesion molecules in THP-1 and endothelial cells

Interaction between leukocyte and endothelial cells (ECs) is essential for vascular homeostasis and competent immune-inflammatory responses in vivo. Platelet-derived microparticles (PMPs) are generated by high shear stress and may appear in diseased small arteries and arterioles in various clinical settings. In this study, we used flow cytometry and confocal laser scanning microscopy to investigate the effects of high-shear-induced platelet and microparticle activation in adhesion molecules of THP-1 and ECs. We also measured the production of some cytokines and studied cytokine mRNA from THP-1 and ECs after PMP stimulation. PMP stimulation of THP-1 cells increased CD11b, CD32, and CD33 but not CD29, CD31, and CD36. PMP stimulation of ECs increased CD54 and CD63 but not CD9, CD29, and CD31. PMPs induced interleukin-8 (IL-8), interleukin-1 beta (IL-1 beta), and tumor necrosis factor alpha (TNF alpha) production by THP-1. PMPs also induced IL-8, IL-1 beta, and interleukin-6 (IL-6) production by ECs. Production was time-dependent. With RT-PCR, some cytokine mRNAs were detected in THP-1 and ECs after PMP stimulation. In relation to adhesiveness after PMP stimulation, we could clearly observe a shift in distribution not only of CD11b in THP-1 cells but also of CD54 in ECs. In addition, anti-P-selectin glycoprotein ligand-1 antibody reduced the expression of CD11b, CD32, and CD33 in THP-1 after PMP stimulation. These results suggest that high-shear-induced microparticles may contribute to the development of atherosclerosis and participate in vascular damage in inflammatory disorders.

Microvascular coagulopathy and disseminated intravascular coagulation

OBJECTIVE

To review the dual characteristics of disseminated intravascular coagulation (DIC), as both a contributor to multiple organ failure as well as a symptom of severe underlying disease associated with systemic vascular changes.

DATA SOURCES

Published literature data and unpublished results from the authors.

DATA SUMMARY

Clinical and experimental studies strongly suggest that DIC contributes to multiple organ failure and death in patients with severe systemic disorders such as sepsis. DIC is evoked by systemic cytokine activity, and the inflammatory response aggravates vascular permeability, inflammation, and cell damage in tissues. In addition to intravascular fibrin formation, thrombin and fibrin generation in tissues is also an important aspect of DIC. An example of DIC at the organ level is adult respiratory distress syndrome, where fibrin in the lung is a characteristic feature. Intravascular fibrin formation and occlusion may elicit a hypoxic response with induction of hypoxia related transcription factors. The resulting ischemic preconditioning may offer protective effects to the involved organ(s).

CONCLUSIONS

Overall, the beneficial or harmful effects of activated coagulation and fibrin formation for organ pathology and recovery from DIC remain to be explored. This may be a critical element in the assessment of ischemia-reperfusion effects of specific anticoagulant therapy.

Protein C replacement in severe meningococcemia: rationale and clinical experience

Severe meningococcemia, which is associated with hemodynamic instability, purpura fulminans and disseminated intravascular coagulation, still has a high mortality rate, and patients who survive are often left invalids because of amputations and organ failure. Clinical studies have shown that levels of protein C are markedly decreased in patients with severe meningococcemia and that the extent of the decrease correlates with a negative clinical outcome. There is a growing body of data demonstrating that activated protein C, in addition to being an anticoagulant, is also a physiologically relevant modulator of the inflammatory response. The dual function of protein C may be relevant to the treatment of individuals with severe meningococcal sepsis. In the present review we give a basic overview of the protein C pathway and its anticoagulant activity, and we summarize experimental data showing that activated protein C replacement therapy clearly reduces the mortality rate for fulminant meningococcemia.

Collection of MNCs with two cell separators for adoptive immunotherapy in patients with stage IV melanoma

BACKGROUND

MNCs for adoptive immunotherapy may be collected by leukocytapheresis with a cell separator.

STUDY DESIGN AND METHODS

Six healthy cytapheresis donors donated two MNC concentrates on a cell separator (AS.TEC 204, Fresenius): one on the standard MNC program and one on a modified MNC program with reduced centrifuge velocity that leads to a lower platelet contamination. Seventeen patients with malignant melanoma donated 26 MNC concentrates: 5 on the AS.TEC 204 MNC program, 9 on the modified AS.TEC 204 MNC program, and 12 on another modified MNC program (Spectra, COBE).

RESULTS

In the course of cultivation of MNCs to dendritic cells (DCs), the donor MNC concentrates with the lower platelet contamination (475 +/- 85 x 10(9)/L) had a significantly higher relative DC yield (low platelet contamination: 3.9 +/- 1.6% of the plated cells; high platelet contamination: 2.5 +/- 1.8% of the plated cells; p = 0.019) than the concentrates with the higher platelet contamination (2364 +/- 448 x 10(9)/L). No significant difference was found in the yields of MNCs and CD14+ cells in the three protocols used for the collection of MNCs from patients with melanoma. The components obtained by the standard AS.TEC 204 MNC program had a significantly higher platelet contamination (1768 +/- 994 x 10(9)/L) than the components obtained by the modified AS.TEC MNC program (360 +/- 98 x 10(9)/L; p<0.05) and the modified Spectra MNC program (636 +/- 266 x 10(9)/L); p<0.05). Because of the low number of investigated components, no significant difference in the DC yield of the three protocols could be detected (mean DC yield after cultivation: 746 +/- 429 x 10(6)).

CONCLUSION

A high platelet contamination of MNC concentrates intended for adoptive immunotherapy can lead to a significant impairment of the DC yield after cultivation. Both the modified AS.TEC 204 and the modified Spectra MNC programs are well suited for collecting MNC concentrates with high MNC yields and low platelet contamination from patients with malignant melanoma.

Thrombin and leukocyte recruitment in endotoxemia

Because thrombin has been implicated in sepsis, it has been proposed that antithrombin III (AT III) is beneficial due to its anticoagulatory and antiadhesive effects. Using intravital microscopy, we visualized leukocyte-endothelium interactions in postcapillary venules of the feline mesentery exposed to lipopolysaccharide (LPS). At a concentration of AT III that blocks leukocyte adhesion in postischemic mesentery, we found no role for thrombin in LPS-induced rolling, adhesion and emigration, or microvascular dysfunction. Furthermore, AT III did not attenuate leukocyte-endothelial interactions after tumor necrosis factor-alpha superfusion of the mesentery. In contrast, fucoidan, a selectin inhibitor, prevented almost all LPS-induced rolling and reduced adhesion, emigration, and microvascular dysfunction. In a model of endotoxemia, leukocyte recruitment into mesentery or lungs was unaffected by AT III. Finally, in a human cell system that mimics the flow conditions in vivo, human neutrophils rolled, adhered, and emigrated similar to the feline postcapillary microvessels, and AT III had no effect on leukocyte recruitment induced by LPS. If AT III has beneficial effects in endotoxemia, it is not due to a direct effect upon leukocyte rolling, adhesion, or emigration in postcapillary venules in vivo.

Thrombocyte HLA molecules retain nonrenewable endogenous peptides of megakaryocyte lineage and do not stimulate direct allocytotoxicity in vitro

The origin and the function of HLA class I molecules present on the surface of human platelets are still unclear. In particular, it is controversial which fraction of these class I molecules represents integral membrane components derived from the megakaryocyte-platelet lineage versus soluble plasma HLA molecules acquired by adsorption. Results of the present study show that HLA-A2 ligands isolated from platelets possess the same peptide motif as described for HLA-A2-associated peptides obtained from nucleated cells. Sequencing of these platelet-derived peptides reveals that they originate mainly from ubiquitously expressed proteins also present in the megakaryocyte-platelet lineage. Moreover, one of these peptides derives from the GPIX protein, which is specifically expressed by platelets and their precursors. Platelet HLA molecules are unstable in vitro at 37°C, but can be partially stabilized by addition of exogenous β2-microglobulin and HLA class I binding peptide, suggesting that platelets cannot load HLA molecules with endogenous peptides. In in vitro experiments platelets were used to stimulate peripheral blood mononuclear cells. No allospecific cytotoxicity was observed after primary stimulation, or secondary restimulation, with allogenic resting or activated platelets, even in the presence of additional third-party helper activity. These data indicate that HLA class I molecules from platelets cannot directly induce allogenic CD8+ cytotoxic T-cell response in vitro.

Thrombocyte HLA molecules retain nonrenewable endogenous peptides of megakaryocyte lineage and do not stimulate direct allocytotoxicity in vitro

The origin and the function of HLA class I molecules present on the surface of human platelets are still unclear. In particular, it is controversial which fraction of these class I molecules represents integral membrane components derived from the megakaryocyte-platelet lineage versus soluble plasma HLA molecules acquired by adsorption. Results of the present study show that HLA-A2 ligands isolated from platelets possess the same peptide motif as described for HLA-A2-associated peptides obtained from nucleated cells. Sequencing of these platelet-derived peptides reveals that they originate mainly from ubiquitously expressed proteins also present in the megakaryocyte-platelet lineage. Moreover, one of these peptides derives from the GPIX protein, which is specifically expressed by platelets and their precursors. Platelet HLA molecules are unstable in vitro at 37°C, but can be partially stabilized by addition of exogenous β2-microglobulin and HLA class I binding peptide, suggesting that platelets cannot load HLA molecules with endogenous peptides. In in vitro experiments platelets were used to stimulate peripheral blood mononuclear cells. No allospecific cytotoxicity was observed after primary stimulation, or secondary restimulation, with allogenic resting or activated platelets, even in the presence of additional third-party helper activity. These data indicate that HLA class I molecules from platelets cannot directly induce allogenic CD8+ cytotoxic T-cell response in vitro.

White cell apoptosis in platelet concentrates

BACKGROUND

The aim of the present study was the evaluation of the apoptosis in residual white cells (WBCs) contained in platelet concentrates (PCs) and of the relationship of this apoptosis with the concentration of inflammatory cytokines in the medium and with platelet activation.

STUDY DESIGN AND METHODS

Three independent methods were used to evaluated apoptosis in WBCs present in 9 PCs, either from single donors by apheresis (SD-PCs) or from pooled buffy coats (BC-PCs). All PCs were divided in two parts, one of which was irradiated. PCs were stored up to 4 days at room temperature, and samples were withdrawn daily for analysis of apoptosis, of platelet activation (surface and soluble CD62P), and of cytokine concentration (interleukin [IL]-1alpha, IL-1beta, IL-6, IL-8, and tumor necrosis factor alpha).

RESULTS

Apoptosis was found to occur with storage in both irradiated and nonirradiated units. Platelet activation increased with storage time and was higher in BC-PCs. The amount of released cytokines was rather variable among PC units. Only IL-8 was consistently found to increase with storage time.

CONCLUSIONS

Apoptosis of residual WBCs occurred in PC units as a function of storage time. The amount and the time course of apoptosis seem to correlate with IL-8 release rather than with platelet activation or with the occurrence of febrile nonhemolytic transfusion reactions.

Activation of peripheral CB1 cannabinoid receptors in haemorrhagic shock

Anandamide, an endogenous cannabinoid ligand, binds to CB1 cannabinoid receptors in the brain and mimics the neurobehavioural actions of marijuana. Cannabinoids and anandamide also elicit hypotension mediated by peripheral CB1 receptors. Here we report that a selective CB1 receptor antagonist, SR141716A, elicits an increase in blood pressure in rats subjected to haemorrhagic shock, whereas similar treatment of normotensive rats or intracerebroventricular administration of the antagonist during shock do not affect blood pressure. Blood from haemorrhaged rats causes hypotension in normal rats, which can be prevented by SR141716A but not by inhibition of nitric oxide synthase in the recipient. Macrophages and platelets from haemorrhaged rats elicit CB1 receptor-mediated hypotension in normotensive recipients, and incorporate arachidonic acid or ethanolamine into a product that co-elutes with anandamide on reverse-phase high-performance liquid chromatography. Also, macrophages from control rats stimulated with ionomycin or bacterial phospholipase D produce anandamide, as identified by gas chromatography and mass spectrometry. These findings indicate that activation of peripheral CB1 cannabinoid receptors contributes to haemorrhagic hypotension, and anandamide produced by macrophages may be a mediator of this effect.