Anti-HLA Class I alloantibodies in platelet transfusion refractoriness: From mechanisms and determinants to therapeutic prospects

Patients with hematological disorders and severe thrombocytopenia require extensive and iterative platelet transfusion support. In these patients, platelet transfusion refractoriness represents a serious adverse transfusion event with major outcomes for patient care. Recipient alloantibodies against the donor HLA Class I antigens expressed at the cell surface of platelets result in a rapid removal of transfused platelets from the circulation and thus, therapeutic and prophylactic transfusion failure leading to a major bleeding risk. In this case, the only way to support the patient relies on the selection of HLA Class I compatible platelets, an approach restricted by the limited number of HLA-typed donors available and the difficulty of meeting the demand in an emergency. However, not all patients with anti-HLA Class I antibodies develop refractoriness to platelet transfusions, raising the question of the intrinsic characteristics of the antibodies and the immune-mediated mechanisms of platelet clearance associated with a refractory state. In this review, we examine the current challenges in platelet transfusion refractoriness and detail the key features of the antibodies involved that should be considered. Finally, we also provide an overview of future therapeutic strategies.

Discriminating young platelets on human leukocyte antigen-I expression highlights their extremely high reactivity potential

Background

The platelet population is heterogeneous, with different subsets that differ on the basis of their function and reactivity. An intrinsic factor participating in this difference of reactivity could be the platelet age. The lack of relevant tools allowing a formal identification of young platelets prevents so far to draw solid conclusions regarding platelet reactivity. We recently reported that human leukocyte antigen-I (HLA-I) molecules are more expressed on human young platelets.

Objectives

The aim of this study was to assess platelet reactivity according to their age based on HLA-I expression level.

Methods

Platelet activation was assessed by flow cytometry (FC) for different platelet subsets based on their HLA-I expression. These populations were further cell sorted and their intrinsic properties were determined by FC and electron microscopy (EM). Statistical analyses were performed with GraphPad Prism 5.02 software using two-way ANOVA followed by a Tukey post hoc test.

Results

HLA-I expression level allowed the identification of 3 platelet subpopulations regarding to their age (HLA low, dim, and high). HLA-I was reliable to guide platelet cell sorting and highlighted the features of young platelets in the HLA-I^high population. In response to different soluble agonists, HLA-I^high platelets were the most reactive subset as shown by the level of P-selectin secretion and fibrinogen binding assessed by flow cytometry. Moreover, the highest capacity of HLA-I^high platelets to simultaneously express annexin-V and von Willebrand factor or activated αIIbβ3 after coactivation with TRAP and CRP indicated that the procoagulant feature of platelets was age-related.

Conclusion

The young HLA-I^high population is the most reactive and prone to become procoagulant. These results open up new perspectives to investigate deeply the role of young and old platelets.

Treatment of congenital thrombocytopenia and decreased collagen reactivity in G6b-B-deficient mice

Mice lacking the immunoreceptor tyrosine-based inhibition motif-containing co-inhibitory receptor G6b-B (Mpig6b, G6b knockout, KO) are born with a complex megakaryocyte (MK) per platelet phenotype, characterized by severe macrothrombocytopenia, expansion of the MK population, and focal myelofibrosis in the bone marrow and spleen. Platelets are almost completely devoid of the glycoprotein VI (GPVI)-FcRγ-chain collagen receptor complex, have reduced collagen integrin α2β1, elevated Syk tyrosine kinase activity, and a subset has increased surface immunoglobulins. A similar phenotype was recently reported in patients with null and loss-of-function mutations in MPIG6B. To better understand the cause and treatment of this pathology, we used pharmacological- and genetic-based approaches to rescue platelet counts and function in G6b KO mice. Intravenous immunoglobulin resulted in a transient partial recovery of platelet counts, whereas immune deficiency did not affect platelet counts or receptor expression in G6b KO mice. Syk loss-of-function (R41A) rescued macrothrombocytopenia, GPVI and α2β1 expression in G6b KO mice, whereas treatment with the Syk kinase inhibitor BI1002494 partially rescued platelet count but had no effect on GPVI and α2β1 expression or bleeding. The Src family kinase inhibitor dasatinib was not beneficial in G6b KO mice. In contrast, treatment with the thrombopoietin mimetic romiplostim rescued thrombocytopenia, GPVI expression, and platelet reactivity to collagen, suggesting that it may be a promising therapeutic option for patients lacking functional G6b-B. Intriguingly, GPVI and α2β1 expression were significantly downregulated in romiplostim-treated wild-type mice, whereas GPVI was upregulated in romiplostim-treated G6b KO mice, suggesting a cell intrinsic feedback mechanism that autoregulates platelet reactivity depending on physiological needs.

Recommandations formalisées d’experts pour la prise en charge des pneumothorax spontanés primaires

Introduction : Le pneumothorax spontané primaire (PSP) est un épanchement gazeux dans la cavité pleurale, survenant hors traumatisme et pathologie respiratoire connue. Des recommandations formalisées d'experts sur le sujet sont justifiées par les pluralités de moyens diagnostiques, stratégies thérapeutiques et disciplines médicochirurgicales intervenant dans leur prise en charge.

Méthodes : Revue bibliographique, analyse de la littérature selon méthodologie GRADE (Grading of Recommendation Assessment, Development and Evaluation) ; propositions de recommandations cotées par experts, patients et organisateurs pour obtenir un consensus. Seuls les avis d'experts avec accord fort ont été retenus.

Résultats : Un décollement sur toute la hauteur de la ligne axillaire et supérieur ou égal à 2 cm au niveau du hile à la radiographie thoracique de face définit la grande abondance. La stratégie thérapeutique dépend de la présentation clinique : exsufflation en urgence pour PSP suffocant ; en l'absence de signe de gravité : prise en charge conservatrice (faible abondance), exsufflation ou drainage (grande abondance). Le traitement ambulatoire est possible si organisation en amont de la filière. Les indications, procédures chirurgicales et l'analgésie périopératoire sont détaillées. Les mesures associées, notamment le sevrage tabagique, sont décrites.

Conclusion : Ces recommandations sont une étape de l'optimisation des stratégies de traitement et de suivi des PSP en France.

Platelet FcγRIIA-induced serotonin release exacerbates the severity of transfusion-related acute lung injury in mice

Transfusion-related acute lung injury (TRALI) remains a major cause of transfusion-related fatalities. The mechanism of human antibody-mediated TRALI, especially the involvement of the Fcγ receptors, is not clearly established. Contrary to mice, human platelets are unique in their expression of the FcγRIIA/CD32A receptor, suggesting that our understanding of the pathogenesis of antibody-mediated TRALI is partial, as the current murine models incompletely recapitulate the human immunology. We evaluated the role of FcγRIIA/CD32A in TRALI using a humanized mouse model expressing the FcγRIIA/CD32A receptor. When challenged with a recombinant chimeric human immunoglobulin G1/mouse anti-major histocompatibility complex class I monoclonal antibody, these mice exhibited exacerbated alveolar edema and higher mortality compared with wild-type (WT) mice. Unlike in WT mice, monocytes/macrophages in CD32A+ mice were accessory for TRALI initiation, indicating the decisive contribution of another cell type. Platelet activation was dramatically increased in CD32A+ animals, resulting in their increased consumption and massive release of their granule contents. Platelet depletion prevented the exacerbation of TRALI in CD32A+ mice but did not affect TRALI in WT animals. By blocking platelet serotonin uptake with fluoxetine, we showed that the severity of TRALI in CD32A+ mice resulted from the serotonin released by the activated platelets. Furthermore, inhibition of 5-hydroxytryptamine 2A serotonin receptor with sarpogrelate, before or after the induction of TRALI, abolished the aggravation of lung edema in CD32A+ mice. Our findings show that platelet FcγRIIA/CD32A activation exacerbates antibody-mediated TRALI and provide a rationale for designing prophylactic and therapeutic strategies targeting the serotonin pathway to attenuate TRALI in patients.

Cell surface expression of HLA I molecules as a marker of young platelets

BACKGROUND

Accurate identification of the proportion of young platelets is important to distinguish peripheral thrombocytopenia from a deficit in platelet production. Young platelets are defined by their higher RNA content and are often assessed as thiazole orange bright (TObright ) by flow cytometry. In clinical practice, their proportion is estimated by automatic blood counter according to their greater RNA content, which identifies a so-called immature platelet fraction (IPF). However, the detected IPFs are not strictly identical to the young TObright platelet population observed by flow cytometry.

OBJECTIVES

The aim of this study was to assess the reliability of HLA I/major histocompatibility I (MHC I) cell surface expression as a marker of young platelets.

METHODS

The HLA I/MHC I expression was evaluated by flow cytometry after costaining blood with TO and antibodies directed against HLA I/MHC I molecules.

RESULTS

We found that platelets with a higher expression of plasma membrane-localized MHC I molecules displayed an increased TO staining and a higher content in ribosomal P-antigen. Transfusion experiments in mice showed that the number of MHC I molecules expressed on the cell surface of young murine platelets decreased during platelet aging, reaching basal levels within 24 h. Finally, we demonstrated that for patients with thrombocytopenias, the identification of young platelets is better assessed by the flow cytometric determination of the level of HLA I expression than by TO staining or the use of hematological blood counter.

CONCLUSION

Overall, our results highlight the relevance of MHC I/HLA I expression as a valuable parameter to identify young platelets.

Platelets are dispensable for antibody-mediated transfusion-related acute lung injury in the mouse

Essentials Role of platelets in immunological transfusion-related acute lung injury (TRALI) is debated. Immunological TRALI was tested in mice exhibiting severe thrombocytopenia or platelet dysfunction. Platelets are required to prevent lung hemorrhage but not edema formation and respiratory distress. Platelets are dispensable for the initiation and development of TRALI.

SUMMARY

Background Transfusion-related acute lung injury (TRALI) is a serious transfusion-related complication. Previous conflicting studies have indicated that platelets are either crucial or dispensable for TRALI. Objectives To evaluate the role of platelets in major histocompatibility complex (MHC) I-induced-TRALI. Methods Antibody-mediated TRALI was experimentally induced in mice by lipopolysaccharide priming followed by the administration of an anti-MHC I mAb. Results TRALI was tested in the context of severe thrombocytopenia provoked by the administration of diphtheria toxin (DT) in transgenic iDTR mice selectively expressing DT receptor in megakaryocytes. The pathologic responses occurring within the first 10 min following the injection of the anti-MHC I mAb, i.e. the severity of lung edema and the drop in aortic blood oxygenation, were similar in severely thrombocytopenic DT-iDTR and control mice. At later times, mortality was nevertheless increased in DT-iDTR mice, owing to lung hemorrhages. When less severe thrombocytopenia was induced with an antiplatelet mAb, TRALI started and developed similarly as in control mice, but hemorrhages were absent. Furthermore, when platelet functions were defective because of administration of aspirin or clopidogrel, or because of glycoprotein (GP)IIbIIIa deficiency, TRALI still developed but no lung hemorrhages were observed. In contrast, when GPVI was immunodepleted, TRALI still occurred, but was occasionally accompanied by hemorrhages. Conclusions Platelets are dispensable for the initiation and development of MHC I-induced TRALI. Although they do not protect against the disruption of the vascular endothelial cell barrier and the subsequent plasma leakage and edema formation, platelets are essential to prevent more serious damage resulting in hemorrhages in alveoli.

Time-Dependent Decay of mRNA and Ribosomal RNA during Platelet Aging and Its Correlation with Translation Activity

Previous investigations have indicated that RNAs are mostly present in the minor population of the youngest platelets, whereas translation in platelets could be biologically important. To attempt to solve this paradox, we studied changes in the RNA content of reticulated platelets, i.e., young cells brightly stained by thiazole orange (TO^bright), a fluorescent probe for RNAs. We provoked in mice strong thrombocytopenia followed by dramatic thrombocytosis characterized by a short period with a vast majority of reticulated platelets. During thrombocytosis, the TO^bright platelet count rapidly reached a maximum, after which TO^dim platelets accumulated, suggesting that most of the former were converted into the latter within 12 h. Experiments on platelets, freshly isolated or incubated ex vivo at 37°C, indicated that their “RNA content”, here corresponding to the amounts of extracted RNA, and the percentage of TO^bright platelets were positively correlated. The “RNA Content” normalized to the number of platelets could be 20 to 40 fold higher when 80–90% of the cells were reticulated (20–40 fg/platelet), than when only 5–10% of control cells were TO^bright (less than 1fg/platelet). TO^bright platelets, incubated ex vivo at 37°C or transfused into mice, became TO^dim within 24 h. Ex vivo at 37°C, platelets lost about half of their ribosomal and beta actin RNAs within 6 hours, and more than 98% of them after 24 hours. Accordingly, fluorescence in situ hybridization techniques confirmed the presence of beta actin mRNAs in most reticulated-enriched platelets, but detected them in only a minor subset of control platelets. In vitro, constitutive translation decreased considerably within less than 6 hours, questioning how protein synthesis in platelets, especially in non-reticulated ones, could have a biological function in vivo. Nevertheless, constitutive transient translation in young platelets under pathological conditions characterized by a dramatic increase in circulating reticulated platelets could deserve to be investigated.

The P2X1 receptor is required for neutrophil extravasation during lipopolysaccharide-induced lethal endotoxemia in mice

Extracellular ATP is becoming increasingly recognized as an important regulator of inflammation. However, the known repertoire of P2 receptor subtypes responsible for the proinflammatory effects of ATP is sparse. We looked at whether the P2X1 receptor, an ATP-gated cation channel present on platelets, neutrophils, and macrophages, participates in the acute systemic inflammation provoked by LPS. Compared with wild-type (WT) mice, P2X1(-/-) mice displayed strongly diminished pathological responses, with dampened neutrophil accumulation in the lungs, less tissue damage, reduced activation of coagulation, and resistance to LPS-induced death. P2X1 receptor deficiency also was associated with a marked reduction in plasma levels of the main proinflammatory cytokines and chemokines induced by LPS. Interestingly, macrophages and neutrophils isolated from WT and P2X1(-/-) mice produced similar levels of proinflammatory cytokines when stimulated with LPS in vitro. Intravital microscopy revealed a defect in LPS-induced neutrophil emigration from cremaster venules into the tissues of P2X1(-/-) mice. Using adoptive transfer of immunofluorescently labeled neutrophils from WT and P2X1(-/-) mice into WT mice, we demonstrate that the absence of the P2X1 receptor on neutrophils was responsible for this defect. This study reveals a major role for the P2X1 receptor in LPS-induced lethal endotoxemia through its critical involvement in neutrophil emigration from venules.

[Pleuropneumonia due to Mycobacterium chelonae]

Mycobacterium chelonae (M. chelonae) is rarely responsible for respiratory infection. This report concerns the case of an 81-year-old man with previously asymptomatic bronchiectasis, colonised by M. chelonae for 3 years. He was hospitalised for acute dyspnoea and fever due to a right hydro-pneumothorax with cavitated alveolar opacities of the right lung. Pleural fluid and bronchial aspiration were positive for M. chelonae and no other microorganisms were detected. The effusion was drained and the patient treated with clarythromycin and amikacin. The radiological abnormalities improved but the patient's general condition remained poor. Treatment was continued for 11 months. Because of the absence of any other bacteria, clinical deterioration following broad-spectrum antibiotics and stabilisation of the lesions after anti-mycobacterial treatment, our diagnosis was severe M. chelonae pleuro-pneumonia in an immunocompetent patient.

Open trial of ciclosporin treatment for Stevens-Johnson syndrome and toxic epidermal necrolysis

Background Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN)are acute mucocutaneous reactions associated with poor prognosis. The treatment is mainly symptomatic, based on supportive care. Until now, several curative treatments have been proposed without evidence of effectiveness.Objectives To evaluate the effect of ciclosporin on SJS and TEN after a short series had suggested a benefit.Methods We conducted an open, phase II trial to determine the safety and possible benefit of ciclosporin. Among the 45 consecutive patients admitted for SJS /TEN from March 2005 to September 2007, 29 fulfilled inclusion criteria. Ciclosporin was administered orally (3 mg kg)1 daily for 10 days) and tapered over a month. Clinical and biological evaluations were performed sequentially. Predicted death rate was estimated with a validated prognostic score (SCORTEN).Results Twenty-nine patients were included at a mean +/- SD of 2.8 +/- 1.8 days after onset. The final diagnosis was SJS (n = 10), SJS ⁄TEN overlap (n = 12) and TEN(n = 7). One month of treatment was completed in 26. Ciclosporin was stopped after more than 10 days in three cases for side-effects including posterior leucoencephalopathy (n = 1), neutropenia (n = 1) and nosocomial pneumopathy(n = 1). Ciclosporin dosage was tapered earlier than scheduled in two cases for alteration in renal function. The prognostic score predicted 2.75 deaths; none occurred (P = 0.1). Mean epidermal detachment remained stable in 18 of 29 cases (62%). The mean ± SD hospital stay was 16.2 +/- 9.1 days.Conclusions Both the death rate and the progression of detachment seemed lower than expected, suggesting a possible usefulness of ciclosporin in SJS and TEN that needs to be confirmed.

Immature myeloid dendritic cells capture and remove activated platelets from preformed aggregates

BACKGROUND

Immature dendritic cells (DCs) patrol the circulation, where they can uptake antigens. It has been reported that mature monocyte-derived DCs have the ability to interact with an activated platelet monolayer under high shear conditions (1500s(-1) ).

OBJECTIVES

In this study, we investigated whether platelets can recruit immature myeloid DCs (CD1c(+) ) directly isolated from blood (BDCs) and if so, which receptors are involved.

RESULTS

Using flow cytometry and electron microscopy, we showed that BDCs interact with activated but not resting platelets in suspension. Interaction was also observed after perfusing BDCs under low flow conditions (150 s(-1) ) through collagen-coated microcapillaries in which platelets had adhered and formed aggregates. No such interaction could be detected at higher shear rates. Whereas initial transient attachment required the exposure of P-selectin on activated platelets and PSGL-1 on BDCs, subsequent stationary adhesion was dependent on α(IIb) β(3) and α(M) β(2) integrins on platelets and BDCs, respectively. Moreover, during their transient interaction, BDCs preferentially removed platelets located at the outer margin of the thrombus in a P-selectin- and integrin-dependent manner.

CONCLUSION

This study provides evidence for an interaction between activated platelets and immature myeloid DCs only under low shear conditions. This could be of importance for BDC maturation and antigen uptake during normal hemostasis or in the context of atherothrombosis at sites of reduced blood flow.

Elevated levels of MMP-9 and TIMP-1 in the cerebrospinal fluid of neuro-Behçet's disease

Matrix metalloproteinases (MMP-) are involved in leukocyte invasion into the central nervous system (CNS) during inflammation. In a retrospective cohort study of 18 neuro-BD patients, CSF samples were studied for MMP-9, TIMP-1 and cell characteristics in neuro-BD patients compared to 12 Headache attributed to BD (HaBD) patients, 15 multiple sclerosis (MS) and 20 Non-inflammatory Neurological Disease (NIND) patients. Concentrations of MMP-9 and TIMP-1 were measured in CSF by using an enzyme-linked immunosorbent assay (ELISA). The MMP-9/TIMP-1 ratio was significantly increased in neuro-BD group (mean +/- SD: 0.145+/-0.045) compared to (HaBD) (0.065+/-0.029; p=0.0001) and NIND patients (0.070+/-0.031; p=0.0001). No significant differences were observed between neuro-BD and MS patients. A significant correlation was observed between CSF-PMN cells and MMP-9 in neuro-BD patients (r=0.714; p=0.0009), indicating probably that PMN cells were in part the source of MMP-9. A significantly positive correlation was also observed between MMP-9 and CSF-mononuclear cells in neuro-BD patients (r=0.623; p=0.0012). This is the first study to evaluate the expression of matrix metalloproteinase-9 and tissue inhibitors of metalloproteinase-1 in cerebrospinal fluid of neuro-BD patients. It demonstrates increased matrix metalloproteinase-9/tissue inhibitors of metalloproteinase-1 ratio. The results suggested that MMPs released in the CSF may be involved in the pathogenesis of neuro-BD by promoting local damage, similarly as suspected in other inflammatory diseases.

Control of the intracellular pathway of CD1e

CD1e is a membrane-associated protein predominantly detected in the Golgi compartments of immature human dendritic cells. Without transiting through the plasma membrane, it is targeted to lysosomes (Ls) where it remains as a cleaved and soluble form and participates in the processing of glycolipidic antigens. The role of the cytoplasmic tail of CD1e in the control of its intracellular pathway was studied. Experiments with chimeric molecules demonstrated that the cytoplasmic domain determines a cellular pathway that conditions the endosomal cleavage of these molecules. Other experiments showed that the C-terminal half of the cytoplasmic tail mediates the accumulation of CD1e in Golgi compartments. The cytoplasmic domain of CD1e undergoes monoubiquitinations, and its ubiquitination profile is maintained when its N- or C-terminal half is deleted. Replacement of the eight cytoplasmic lysines by arginines results in a marked accumulation of CD1e in trans Golgi network 46+ compartments, its expression on the plasma membrane and a moderate slowing of its transport to Ls. Fusion of this mutated form with ubiquitin abolishes the accumulation of CD1e molecules in the Golgi compartments and restores the kinetics of their transport to Ls. Thus, ubiquitination of CD1e appears to trigger its exit from Golgi compartments and its transport to endosomes. This ubiquitin-dependent pathway may explain several features of the very particular intracellular traffic of CD1e in dendritic cells compared with other CD1 molecules.

Assistance of microbial glycolipid antigen processing by CD1e

Complexes between CD1 molecules and self or microbial glycolipids represent important immunogenic ligands for specific subsets of T cells. However, the function of one of the CD1 family members, CD1e, has yet to be determined. Here, we show that the mycobacterial antigens hexamannosylated phosphatidyl-myo-inositols (PIM6) stimulate CD1b-restricted T cells only after partial digestion of the oligomannose moiety by lysosomal alpha-mannosidase and that soluble CD1e is required for this processing. Furthermore, recombinant CD1e was able to bind glycolipids and assist in the digestion of PIM6. We propose that, through this form of glycolipid editing, CD1e helps expand the repertoire of glycolipidic T cell antigens to optimize antimicrobial immune responses.

The cellular pathway of CD1e in immature and maturing dendritic cells

Dendritic cells (DCs) present antigens to T cells via CD1, HLA class I or class II molecules. During maturation, HLA class II-restricted presentation is optimized. The relocalization of CD1e from Golgi to endosomal compartments during DC maturation suggests also an optimization of the antigen-presentation pathway via CD1 molecules. We here detail the biosynthesis and cellular pathway of CD1e in immature and maturing DCs. Unlike the other CD1 molecules, CD1e was found to reach late endosomes through sorting endosomes, without passing through the plasma membrane in either immature or maturing cells. After induction of DC maturation, CD1e disappeared rapidly from the Golgi and was transiently localized in HLA-DR+ vesicles, while the number of CD1e+/CD1b+ compartments increased for at least 20 h. High-resolution light microscopy showed that, in immature DCs, CD1e+ vesicles were often in close apposition to EEA1+ or HLA-DR+ compartments, while CD1e displayed a nearly exclusive distribution in the lysosomes of mature DCs, a finding corroborated by immunoelectron microscopy. During maturation, CD1e synthesis progressively declined, while the endosomal cleavage of CD1e still occurred. Thus, CD1e displays peculiar properties, suggesting an unexpected role among the family of CD1 antigen-presenting molecules.

Common characteristics of the human and rhesus macaque CD1e molecules: conservation of biochemical and biological properties during primate evolution

In humans, a family of five genes encodes the CD1 molecules. Four of these proteins, CD1a, b, c, and d, are expressed on the plasma membrane and traffic between the cell surface and endocytic compartments, where they are loaded with antigenic glycolipids. The existence of human CD1e was demonstrated recently. This molecule surprisingly remains inside the cell, accumulating mainly in the Golgi compartments of immature dendritic cells and in the late endosomes of mature dendritic cells. In the latter compartments, CD1e is cleaved and becomes soluble. To determine whether these properties were specific to human CD1e, we investigated the presence and characteristics of CD1e in the rhesus macaque, an evolutionarily distant species of the primate lineage. Our results show that the cellular and biochemical properties of the human and simian CD1e molecules are similar, suggesting that the particular intracellular distribution of CD1e is important for its physiological and/or immunological function.

Imbalance between platelet vascular endothelial growth factor and platelet-derived growth factor in pulmonary hypertension. Effect of prostacyclin therapy

Focal vascular injury and impaired endothelial function are features of pulmonary hypertension (PH) that lead to enhanced platelet endothelial cell interactions. Vascular endothelial growth factor (VEGF) is contained in platelets and released at sites of vascular injury to promote endothelial repair and wound healing in combination with platelet-derived nonspecific mitogens such as platelet-derived growth factor (PDGF). The overall balance between platelet VEGF and PDGF was investigated in 21 patients with primary PH, 8 with secondary PH, and 27 with chronic hypoxemic lung disease (CHLD), as well as in 29 control subjects. Platelet VEGF content was increased in patients with primary and secondary PH as compared with control subjects (518 +/- 89, 675 +/- 156, and 166 +/- 29 fg/10(5) platelets, respectively; p < 0.01), whereas platelet PDGF content was similar in the three groups (31 +/- 2, 36 +/- 4, and 33 +/- 3 pg/10(5) platelets, respectively; NS). Patients treated with a continuous prostacyclin infusion had a higher platelet VEGF but a similar platelet PDGF content as compared with untreated patients. Moderate increases in platelet VEGF and PDGF contents were observed in the CHLD patients. We conclude that patients with primary or secondary PH have an increase in platelet VEGF content, but not in platelet PDGF content, and that their platelet VEGF content increases further in response to prostacyclin infusion. We suggest that imbalance between platelet VEGF and PDGF is beneficial to patients with PH.

Inflammatory cells as well as epithelial cells in nasal polyps express vascular endothelial growth factor

In nasal polyps (NPs), locally secreted growth factors are involved in the remodelling of the epithelium and extracellular matrix but little is known concerning vessel remodelling. The in situ expression of vascular endothelial growth factor (VEGF) in NPs and control nasal mucosa (CM) were evaluated and in vitro secretion of VEGF from primary human cultures of nasal epithelial cells (HNECs) was quantified. VEGF expression was evaluated in NP (n=14) and CM (n=6) after immunolabelling. In supernatants from HNECs cultured at air/liquid interface, VEGF was quantified by immunoassay, under baseline conditions and after transforming growth factor-beta1 (TGF-beta1) stimulation. In HNEC lysates, VEGF and VEGF messenger ribonucleic acid (mRNA) were detected using Western blot analysis and reverse transcriptase polymerase chain reaction respectively. VEGF positivity was more frequent in inflammatory cells in NPs (14 of 14) than in CM (three of six) (p<0.05) and in the epithelium in NPs (six of 14) than in CM (two of six) (nonsignificant). Under baseline conditions, the VEGF concentration in HNEC culture medium increased from day 2 to 4, then decreased and became undetectable. VEGF concentrations increased significantly after TGF-beta1 stimulation. In HNEC lysates, VEGF and VEGF mRNA were detected on days 4 and 14 of culture. It was concluded that vascular endothelial growth factor is intensely expressed in situ in nasal polyps, mainly in inflammatory cells but also in epithelial cells. Human nasal epithelial cells are able to secrete in vitro vascular endothelial growth factor. Transforming growth factor-beta1 upregulates this secretion. This suggests that vascular endothelial growth factor, inducing oedema and angiogenesis, could be involved in the pathogenesis of nasal polyps.

[Coronary gas embolism after laparoscopic surgery]

Gas embolism is a severe complication of laparoscopic surgery. We report two cases: one with lethal peroperative cardiac arrest from massive coronary artery gas embolism recognized during open-chest cardiac massage; the second case, also associated with coronary artery gas embolism, resulted in severe but transient abnormal left ventricular anterior wall motion, subepicardial ischaemia and injury in ECG leads V1 to V5, but unremarkable coronary arteriography and full recovery. The pathophysiology of gas embolism occurring during a laparoscopic procedure, the mechanisms of gas entry into the systemic vascular bed, the clinical, ECG, pulse oximetry, end-tidal CO2 concentration changes and alarm signs are discussed. The diagnostic value of Doppler transoesophageal echocardiography when possible is underlined, and emergency management of gas embolism is considered.

[Diagnosis of pleurisy]

Diagnosis of pleural effusion, suggested by chest pain or dyspnea, is assessed by physical examination, chest X-ray sometimes completed by other imaging techniques, and mainly by thoracentesis. Thoracentesis is mandatory for the diagnostic of pleural effusion as three diagnosis are associated with an emergency treatment: pulmonary embolism; hemothorax; empyema. If the fluid is a transudate, no further invasive studies are necessary. If the cause of pleural exsudat cannot be established by a careful history, physical examination and fluid analysis, generally closed pleural biopsy should be done, followed, in absence of an established diagnosis, by thoracoscopy. At this time, less than 10% of the cases remain without explanation, leading to a careful follow-up of patients since a carcinomatous lesion may develop in 1/3 of them.

Effects of inhibition of catalase and superoxide dismutase activity on antioxidant enzyme mRNA levels

We examined the effects of inhibition of Cu,Zn superoxide dismutase (Cu,Zn SOD) and catalase (Cat) activities on the steady-state mRNA levels of the three major antioxidant enzymes [Cu,Zn SOD, Cat, and glutathione peroxidase (GP)] in human umbilical vein endothelial cells under normoxia and hyperoxia. Inhibition of Cat activity by aminotriazole was not associated with alteration of the other antioxidant enzymes or with potentiation of cell injury. On the other hand, inhibition of Cu,Zn SOD activity by N-N'-diethyl-dithiocarbamate (DDC) was associated with an increase in Cu,Zn SOD mRNA level and a decrease in Cat and GP mRNA level. The combination of DDC and hyperoxia treatments was associated with an additive effect on Cu,Zn SOD message. We propose that these coordinate mRNA changes might be an adaptation to the oxidative environment. This proposal supports the concept that the intracellular O2 metabolites themselves could be the signals that trigger the antioxidant enzymes gene expression.