In vivo regulation of von willebrand factor synthesis: von Willebrand factor production in endothelial cells after lung transplantation between normal pigs and von Willebrand factor-deficient pigs

To evaluate the regulation of plasma von Willebrand factor (vWF) and its in situ production by endothelial cells (ECs), 12 swine leukocyte antigen (SLA)-compatible left lung transplantations were performed. Normal lungs were transplanted into 10 pigs homozygous for von Willebrand disease and into 2 normal pigs. Additionally, 1 normal pig underwent pneumonectomy, and 1 SLA-incompatible lung transplantation between normal pigs was performed. None of the transplanted animals received immunosuppressive therapy. Plasma vWF level was evaluated by ELISA and multimeric pattern. EC vWF content was assessed by immunohistochemistry. Global hemostasis was assessed by standardized ear bleeding time. Six of 12 SLA-compatible lung transplantations and the incompatible transplantation were successful and were used for the study. The functions and the viability of ECs, reflected by their ability to produce vWF and normal multimeric plasma vWF pattern, were preserved in SLA-compatible and -incompatible lung transplantations. vWF production was preserved in ECs that initially synthesized it. EC constitutive and storage pathways are modulated differently according to transplantation compatibility and severity of rejection. In SLA-compatible lung transplantations without histological evidence of rejection, the production of vWF was preserved, whereas constitutive vWF secretion appeared to be altered in cases with minor histological signs of rejection. In pigs with von Willebrand disease that were transplanted with normal lungs without sign of rejection, plasma vWF was significantly increased in an amount expected from the estimated production of a normal lung. In the transplanted normal lung, there was no vWF overexpression by the ECs and no recruitment of ECs that initially did not express vWF. In SLA-incompatible transplantation, ECs were morphologically normal with increased and blurred vWF labeling, whereas plasma vWF levels remained normal, reflecting that EC activation is associated with an increased vWF production with probable diversion to storage pathway. This model depicts the changes of EC regulation of vWF secretion in pig lung transplants. However, this model cannot be directly extrapolated to human organ transplantation because animals did not receive any immunosuppressive therapy, which may be toxic to ECs.

[Infection prevention, a continuous challenge for each of us....]

NEGLECTED PREVENTIVE MEASURES: Well-proven and simple techniques including isolation of identified germ carriers and hand washing are effective means of preventing acquisition of infections in health care units. The problem is the lack of routine application. LIMITING BACTERIAL RESISTANCE: The negative ecological impact of antibiotic therapy can be counterbalanced by limiting dose and duration of treatments and by using well-adapted taking into account the antibiotic spectrum. PROPOSED STRATEGIES: In order to prevent and better control infections, measures for screening, isolation and identification of infected patients as well as measures to reduce unnecessary or poorly-adapted prescriptions are required to limit major changes in individual and collective bacterial ecology. Interesting strategies proposed for improving management of hospital infections include good clinical practice guidelines and prescription recommendations for specific sites of infection and germs, and interdisciplinary work groups involving bacteriologists, pharmacists, hygiene specialists, epidemiologists and health economists.

The PEN5 epitope identifies an oligodendrocyte precursor cell population and pilocytic astrocytomas

PEN5 is a sulfated polylactosamine carbohydrate epitope first described in a subpopulation of mature natural killer cells. Here we report that it is also expressed in a developmentally regulated fashion in human and rat central nervous systems and that its protein carrier is P-selectin glycoprotein ligand-1 (PSGL-1), a ligand for selectins. In rat neural primary cultures, PEN5 is transiently and selectively expressed by oligodendrocyte precursor cells and marks the transition from proliferative to postmitotic stages. In concordance, in human central nervous system tumors, PEN5 is observed in a subset of oligodendrogliomas and in all pilocytic astrocytomas, a class of tumor of uncertain histogenesis. These data suggest that PEN5-PSGL-1 plays a role in the differentiation of oligodendrocytes and that pilocytic astrocytomas are likely to result from a dysregulation occurring in oligodendrocyte precursor cells at the crucial stage of exit from the cell cycle.

A pilot study of iron depletion as adjuvant therapy in chronic hepatitis C patients not responding to interferon

The aim of this study was to assess the efficacy of iron depletion obtained by phlebotomy to enhance interferon response in 11 patients who had failed to respond to a standard 3-month interferon treatment. Despite a significant effect on serum aminotransferase levels, there was no effect on viremia, and iron depletion was unable to trigger interferon response.

Molecular cloning of a lipolysis-stimulated remnant receptor expressed in the liver

The lipolysis-stimulated receptor (LSR) is a lipoprotein receptor primarily expressed in the liver and activated by free fatty acids. Antibodies inhibiting LSR functions showed that the receptor is a heterotrimer or tetramer consisting of 68-kDa (alpha) and 56-kDa (beta) subunits associated through disulfide bridges. Screening of expression libraries with these antibodies led to identification of mRNAs derived by alternate splicing from a single gene and coding for proteins with molecular masses matching that of LSR alpha and beta. Antibodies directed against a synthetic peptide of LSR alpha and beta putative ligand binding domains inhibited LSR activity. Western blotting identified two liver proteins with the same apparent molecular mass as that of LSR alpha and beta. Transient transfections of LSR alpha alone in Chinese hamster ovary cells increased oleate-induced binding and uptake of lipoproteins, while cotransfection of both LSR alpha and beta increased oleate-induced proteolytic degradation of the particles. The ligand specificity of LSR expressed in cotransfected Chinese hamster ovary cells closely matched that previously described using fibroblasts from subjects lacking the low density lipoprotein receptor. LSR affinity is highest for the triglyceride-rich lipoproteins, chylomicrons, and very low density lipoprotein. We speculate that LSR is a rate-limiting step for the clearance of dietary triglycerides and plays a role in determining their partitioning between the liver and peripheral tissues.

Differential regulation of killer cell Ig-like receptors and CD94 lectin-like dimers on NK and T lymphocytes from HIV-1-infected individuals

NK and T lymphocytes share various cell surface receptors, including NK receptors for MHC class I molecules (NKR). NKR include killer cell Ig-like receptors (KIR) and lectin-like dimers which are composed of the invariant CD94 associated with a variety of NKG2 molecules. The combination of KIR and CD94/NKG2 dimers expressed on NK and T cell subsets defines a repertoire of MHC class I recognition. Engagement of NKR by cognate MHC class I molecules governs T and NK cell activation. We investigated the NKR distribution on NK and T cell subsets from uninfected and HIV-infected individuals, according to the clinical status, the absolute numbers of CD4+ T cells as well as the plasmatic viral load of the patients. We show that the KIR distribution on NK cells is not affected by HIV-1 infection, whereas the absolute numbers of T cells expressing specific KIR members (CD158b, p70) transiently increase in early stages of HIV infection. By contrast, the percentages of NK and T cells which express CD94 dimers increase in parallel with the disease. These results document a differential regulation of KIR and CD94 lectin-like dimers during the course of a chronic viral infection in humans and further suggest that both types of NKR are independently regulated.

Six-hour trimethoprim-sulfamethoxazole-graded challenge in HIV-infected patients

BACKGROUND

Hypersensitivity reactions to trimethoprim-sulfamethoxazole (TMP-SMX) are very common in HIV-infected patients, leading to drug discontinuation. However, it is the drug of choice as prophylaxis for Pneumocystis carinii pneumonia.

OBJECTIVES

We sought to determine the safety and long-term efficacy of a 6-hour TMP-SMX-graded challenge in a group of hypersensitive HIV-infected patients.

METHODS

Forty-four consecutive HIV-infected patients with documented TMP-SMX hypersensitivity were seen in our outpatient allergy department. They ingested 12 doses of increasing amounts of TMP-SMX at half-hour intervals. Thereafter, they took 80/400 mg TMP-SMX daily and were advised to "treat through" every nonbullous cutaneous adverse reaction.

RESULTS

All 44 patients tolerated the procedure without any adverse reactions during the day of challenge. Eleven of the 44 patients experienced mild hypersensitivity reactions on days 1 to 2 (8 patients) and 8 to 10 (3 patients), consisting mainly on a 1-day pruritic maculopapular eruption. Two patients stopped TMP-SMX at day 1, and 2 stopped it at days 10 and 15, giving an overall success rate at 1 month of 91% (40 of 44). Two were successfully rechallenged late. After a median follow-up of 10 months, 42 patients were taking TMP-SMX without any adverse reaction, giving an overall success rate of 95%.

CONCLUSIONS

A 6-hour graded challenge with cautious "treating through" of mild reactions enables more patients to take TMP-SMX and is safe and effective.

Effect of weight change and metformin on fibrinolysis and the von Willebrand factor in obese nondiabetic subjects: the BIGPRO1 Study. Biguanides and the Prevention of the Risk of Obesity

OBJECTIVE

Insulin resistance is associated with hypofibrinolysis. Metformin has been shown to improve insulin sensitivity and fibrinolysis. Its action on fibrinolysis and the von Willebrand factor was evaluated in the Biguanides and the Prevention of the Risk of Obesity (BIGPRO)1 trial in nondiabetic men (n = 151) and women (n = 306) aged between 34 and 65 years with a central fat distribution and a mean BMI of 32.5 kg/m2.

RESEARCH DESIGN AND METHODS

The subjects were randomly allocated to a 1-year treatment with metformin (850 mg b.i.d.) or placebo, in addition to diet and exercise recommendations.

RESULTS

Plasminogen activator inhibitor 1 (PAI-1) activity and antigen decreased significantly but similarly by 30 and 40%, respectively, in both the placebo and the metformin groups. This decrease occurred mainly in subjects who lost weight. Metformin did not have any significant additional effect on PAI-1. In contrast to the results for PAI-1, there was a significantly greater decrease in tissue-type plasminogen activator (tPA) antigen in the metformin than in the placebo group (mean+/-SD: -1.1+/-3.1 vs. 0.2+/-3.2 ng/ml, P < 0.02). The von Willebrand factor (vWF) also decreased significantly more in the metformin group (-0.17+/-0.42 vs. -0.05+/-0.38 U/I, P < 0.02).

CONCLUSIONS

Weight loss was the main factor associated with the decrease in PAI-1, in accordance with the recent demonstration of production of PAI-1 by adipocytes. Metformin had a significant effect on two factors, tPA antigen and vWF, mainly secreted by the endothelial cells, which suggests an effect of the drug on the production or the metabolism of these two hemostatic proteins.

An inhibitor of HIV-1 protease modulates proteasome activity, antigen presentation, and T cell responses

Inhibitors of the protease of HIV-1 have been used successfully for the treatment of HIV-1-infected patients and AIDS disease. We tested whether these protease inhibitory drugs exerted effects in addition to their antiviral activity. Here, we show in mice infected with lymphocytic choriomeningitis virus and treated with the HIV-1 protease inhibitor ritonavir a marked inhibition of antiviral cytotoxic T lymphocyte (CTL) activity and impaired major histocompatibility complex class I-restricted epitope presentation in the absence of direct effects on lymphocytic choriomeningitis virus replication. A potential molecular target was found: ritonavir selectively inhibited the chymotrypsin-like activity of the 20S proteasome. In view of the possible role of T cell-mediated immunopathology in AIDS pathogenesis, the two mechanisms of action (i.e., reduction of HIV replication and impairment of CTL responses) may complement each other beneficially. Thus, the surprising ability of ritonavir to block the presentation of antigen to CTLs may possibly contribute to therapy of HIV infections but potentially also to the therapy of virally induced immunopathology, autoimmune diseases, and transplantation reactions.

Single blood donor exposure programme for preterm infants: a large open study and an analysis of the risk factors to multiple donor exposure

As the need for blood transfusions of very preterm infants remains considerable, various strategies are considered to minimize exposure to multiple blood donors along with blood wastage. In a large population of very preterm infants born between 24 and 31 weeks' gestation, we undertook an open study to assess the efficacy of a single blood donor exposure programme and to determine, among the population enrolled in this programme, the risk factors for exposure to multiple donors. One hundred and forty-two neonates were included in a single donor exposure programme with a 35-day expiry date blood unit. Though no inflation in the total number of transfusions was noticed, there was a 55% overall reduction in the total number of required donors. To determine the risk factors for exposure to multiple donors in this population, 114 neonates alive after the expiry date of the first unit of packed red blood cells were selected. The greatest and the most extending transfusion requirements were observed in very preterm infants born before 28 weeks' gestation and in those born after but with an intra-uterine growth retardation below the 10th percentile. Indeed, 70% of those high-risk infants were exposed to a second blood donor and more than 85% of the group exposed to a second donor belonged to this high-risk population.

CONCLUSION

Neonates with a very high risk of a more-than-one donor exposure were born before 28 weeks' gestation or between 28 and 31 weeks but with an intra-uterine growth retardation below the 10th percentile.

Role of plasma and platelet von Willebrand factor in arterial thrombogenesis and hemostasis in the pig

To evaluate the relative role of plasma and platelet von Willebrand factor (vWF) pools in hemostasis and arterial thrombogenesis, pigs with vW disease (vWD) were injected with vWF concentrate and/or grafted with bone marrow from a normal pig. Hemostasis was assessed by measurement of ear immersion bleeding time, factor VIII (FVIII) activity, and plasma and platelet vWF antigen levels. The thrombotic process was explored at 650 s(-1) and 1600 s(-1) in an ex vivo cylindrical perfusion chamber. Pigs with vWD exhibited a prolonged bleeding time (>30 minutes) compared with normal pigs (<5 minutes); in addition, they showed normal platelet adhesion and thrombus formation at 650 s(-1) but profoundly reduced platelet adhesion and thrombus formation at 1600 s(-1). Each experiment was performed before and 3 and 24 hours after injection of vWF concentrate. In our bleeding time study, only plasma vWF restoration induced a partial but delayed correction (24 hours postinjection), which was correlated with the highest measured level of FVIII activity. In the perfusion chamber model, restoration of plasma or platelet vWF pools resulted in similar partial correction of platelet adhesion and average thrombus size. In the perfused pigs, the maximum correction occurred 3 hours postinjection. Platelet deposition reached normal values after vWF concentrate was injected into a grafted pig. The present results suggest that when both plasma and platelet vWF levels are restored in vWD pigs, bleeding time and the thrombotic process are normalized according to different kinetics and with differing degrees of effectiveness.

Effects of human recombinant, plasma-derived and porcine von Willebrand factor in pigs with severe von Willebrand disease

The effects of the infusion of a human recombinant von Willebrand factor (vWF) preparation in pigs homozygous for von Willebrand disease (vWD) were evaluated on serial measurements of von Willebrand factor antigen and activity, FVIII activity, vWF multimer analysis, in-vivo bleeding time and platelet adhesion and thrombus formation on collagen at high shear rates in an ex-vivo model of experimental thrombosis. Plasma-derived human and porcine vWF were used for comparison. Before infusion, the pigs were characterized by undetectable plasma vWF levels, a low level of FVIII, prolonged bleeding time, severely impaired platelet adhesion and thrombus formation. After infusion of the human recombinant vWF, in-vivo recovery of vWF activity ranged from 58% to 82%, depending on the dose infused, and its half-life was longer than for the plasma-derived concentrates. The highest-molecular-weight forms of human recombinant vWF were removed from the circulation gradually. Infusion of the three vWF concentrates produced inconsistent effects on bleeding time and moderate improvement of platelet adhesion and thrombus formation. After infusion, a prolonged increase of FVIII (> 48 h) was observed, suggesting that human recombinant vWF is able to bind and to stabilize porcine factor VIII and that porcine vWD is a good model for studying such interactions.

[Epidemiology of hepatitis C virus infection in 1,304 HCV positive patients: variations according to the origin of transmission and year of diagnosis]

The evolution of epidemiological data on hepatitis C virus infection is poorly documented and thus the impact of screening is difficult to evaluate.

AIM

To study epidemiological variations based on the origin of transmission and the year of diagnosis of hepatitis C virus infection.

METHODS

The files of all 1304 patients seen in the hepatology unit of the Rennes University Hospital were analyzed (retrospectively before and prospectively after October 1995) in relation to epidemiological features.

RESULTS

Despite widespread screening which is the source of 60% of the diagnoses, the total number of new cases of hepatitis C infection per year has not increased. Compared to patients diagnosed in the first years following the discovery of the virus, patients recently identified were younger (42 +/- 14 years) and frequently drug addicts (40%). Aminotransaminases were normal in 20% of cases. The frequency of cirrhosis has declined (17%). There has been a decrease in the proportion of patients who undergo liver biopsy (50%) and treatment with interferon (one third of patients).

CONCLUSIONS

The impact of screening on the number of newly treated patients seems to be lower than previously predicted.

Inhibitory effects of specific apolipoprotein C-III isoforms on the binding of triglyceride-rich lipoproteins to the lipolysis-stimulated receptor

ApoC-III overexpression in mice results in severe hypertriglyceridemia due primarily to a delay in the clearance of triglyceride-rich lipoproteins. We have, in primary cultures of rat hepatocytes, characterized a lipolysis-stimulated receptor (LSR). The apparent number of LSR that are available on rat liver plasma membranes is negatively correlated with plasma triglyceride concentrations measured in the fed state. We therefore proposed that the primary physiological role of the LSR is to contribute to the cellular uptake of triglyceride-rich lipoproteins. We have now tested the effect of apoC-III on the binding of triglyceride-rich lipoproteins to LSR. Supplementation of 125I-very low density lipoprotein (VLDL) with apoC-III inhibited the LSR-mediated binding, internalization, and degradation of 125I-VLDL in primary cultures of rat hepatocytes. Studies using isolated rat liver plasma membranes showed that enrichment of human VLDL and chylomicrons with synthetic or purified human apoC-III decreased their binding to the LSR by about 40%. Supplementation of triglyceride-rich lipoproteins under the same conditions with human apoC-II had no such inhibitory effect, despite the fact that this apoprotein bound as efficiently as apoC-III to these particles. Preincubation of LDL with apoC-III did not modify its binding to LSR. Partitioning studies using 125I-apoC-III showed that this lack of effect was due to apoC-III's inability to efficiently associate with LDL. Purified human apoC-III1 was as efficient as the synthetic nonsialylated form of apoC-III in inhibiting binding of VLDL to LSR. However, despite a 2-fold greater binding of apoC-III2 to VLDL, this isoform was a less efficient inhibitor of the binding of VLDL to LSR than apoC-III1 or nonsialylated apoC-III. Desialylation of apoC-III2 by treatment with neuraminidase increased the inhibition of VLDL binding to LSR to a level similar to that observed with apoC-III1 and nonsialylated apoC-III. We propose that apoC-III regulates in part the rate of removal of triglyceride-rich particles by inhibiting their binding to the LSR, and that the level of inhibition is determined by the degree of apoC-III sialylation.

Flow cytometric sorting and biochemical characterization of the late endosomal rab7-containing compartment

Rab7 is a small molecular weight GTPase that is known to be associated with late endocytic compartments. Studies in which wild-type or mutant forms of this protein have been overexpressed in mammalian cells have indicated that rab7 plays a role in controlling membrane transport between late endocytic compartments. However, both the precise site(s) of action and localization of rab7 remain unclear. In the present study, we have used density-gradient centrifugation in combination with a new epitope-specific flow cytometric sorting method to isolate rab7-containing vesicles from baby hamster kidney (BHK) cells. Electron-micrographs of sorted elements showed a homogeneous population of vesicles that resembles late endosomes. The polypeptide composition of rab7-containing vesicles was then analyzed by two-dimensional (2-D) gel electrophoresis. Rab7-containing vesicles were enriched in the cation-independent mannose 6-phosphate receptor and especially in the precursor forms of cathepsin D. Taken together, these results show that the rab7-containing vesicles are a component of the endocytic pathway that connects late endosomes and lysosomes and in which precursor forms of lysosomal hydrolases, segregated from their receptor, might be included.

[An unknown etiology of fetal ascites: acute intestinal intussusception]

BACKGROUND

Intussusception is a frequent diagnosis during the first year of life. However, it is an uncommon and very rare pathology in neonates and premature infants.

CASE REPORTS

Two full term neonates presented an antenatal intussusception associated with fetal ascites; another premature infant developed an intussusception at the age of 15 days. In the three cases the diagnosis of intussusception had only been established during the laparotomy. A recent review of the literature revealed 13 cases of antenatal intussusception, one of these being associated with fetal ascites.

CONCLUSION

The differential diagnosis of fetal ascites should always include intussusception. Early recognition of this pathology and prompt surgical action would avoid fatalities.

A dominant-negative mutant of the Rab5 GTPase enhances T cell signaling by interfering with TCR down-modulation in transgenic mice

TCR triggering results in the down-modulation of engaged receptors by endocytosis. As a result of this process, Ag-binding sites are depleted from the surface and signaling responses should be attenuated. To test the importance of TCR down-regulation on T cell signaling, we generated mice expressing a dominant-negative form of Rab5 (Rab5N133I) in T cells. Rab5, a monomeric GTPase of the Ras superfamily, has been implicated in the regulation of early steps in the endocytic pathway. In Rab5N133I mice, mature thymocytes developed, but the absolute number of CD4+CD8+ double positive thymocytes was reduced. Fluid phase endocytosis was severely impaired in the transgenic thymocytes. In peripheral T cells, the kinetics and rate of ligand-induced TCR down-modulation were delayed and reduced. These effects were correlated with enhanced early and late signaling responses. Analysis of thymocyte development in doubly transgenic mice for Rab5N133I and a lymphocytic choriomeningitis virus (LCMV) peptide-specific TCR demonstrated that TCR signaling was enhanced by dominant inhibition of Rab5 function, resulting in altered thymic selection. These findings suggest that TCR endocytosis is an important regulatory component of TCR signaling and that defects in this regulation can result in prolonged signaling and alter thymic development.

A dominant-negative mutant of the Rab5 GTPase enhances T cell signaling by interfering with TCR down-modulation in transgenic mice

TCR triggering results in the down-modulation of engaged receptors by endocytosis. As a result of this process, Ag-binding sites are depleted from the surface and signaling responses should be attenuated. To test the importance of TCR down-regulation on T cell signaling, we generated mice expressing a dominant-negative form of Rab5 (Rab5N133I) in T cells. Rab5, a monomeric GTPase of the Ras superfamily, has been implicated in the regulation of early steps in the endocytic pathway. In Rab5N133I mice, mature thymocytes developed, but the absolute number of CD4+CD8+ double positive thymocytes was reduced. Fluid phase endocytosis was severely impaired in the transgenic thymocytes. In peripheral T cells, the kinetics and rate of ligand-induced TCR down-modulation were delayed and reduced. These effects were correlated with enhanced early and late signaling responses. Analysis of thymocyte development in doubly transgenic mice for Rab5N133I and a lymphocytic choriomeningitis virus (LCMV) peptide-specific TCR demonstrated that TCR signaling was enhanced by dominant inhibition of Rab5 function, resulting in altered thymic selection. These findings suggest that TCR endocytosis is an important regulatory component of TCR signaling and that defects in this regulation can result in prolonged signaling and alter thymic development.