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Biomedical subjects

A Capron

Publications and source records attributed to A Capron.

At least 109 records · Page 6Linked to original sources
PubMed1996

Selective CD4+ T cell deletion after specific activation in HIV-infected individuals; protection by anti-CD28 monoclonal antibodies.

AIDS is characterized by a progressive decline in the number of CD4+ T cells. This is preceded by an early selective defect in the proliferation of these cells to recall antigens [1-3], pokeweed mitogen (PWM) [4-6] and to superantigens (SAg) [4,7]. In contrast, the proliferative response to phytohaemagglutinin (PHA) remains intact [1,2,5]. We and others have shown that the proliferative defect in response to some stimuli was in fact due to the induction of cell death [4,7]. The activation-induced cell death mechanism that explains the proliferative defects observed in vitro might also account for the progressive in vivo deletion of CD4+ T cells. Indeed, studies performed on different models of primates have shown that induction of cell death in CD4+ T cells was detected only when T cells were isolated from animals infected with a type of retrovirus that induces an AIDS-like disease [8]. This correlation prompted us to analyse further the mechanism of HIV-induced activation cell death to determine the specificity and rate of induction of cell death. T cells from HIV-infected individuals were activated with superantigens and the V beta T cell receptor (TCR) expression analysed. Data presented here show that cell death is restricted to activated CD4+ T cells, and does not affect bystander cells. More importantly, addition of anti-CD28 MoAb specifically inhibited the induction of apoptosis, raising possibilities for therapy.

Antibodies, Monoclonal↗
PubMed1996

Common cis-acting elements critical for the expression of several genes of Toxoplasma gondii.

Transient transformation of Toxoplasma using the CAT (chloramphenicol acetyl transferase) reporter gene has been used to map promoter elements of four genes encoding dense granule proteins (GRA1, GRA2, GRA5 and GRA6). Intense CAT activities (GRA1 > GRA5 > GRA2 > GRA6) are detected for constructs containing 379bp, 276bp, 209bp and 265bp upstream of the transcription start site of the GRA1, GRA2, GRA5 and GRA6 genes, respectively. Deletion analysis shows that optimal promoter activity of each gene is contained in the proximal region of the transcription start site: -129 to -47 for GRA1, -87 to -37 for GRA2, -156 to -30 for GRA5 and -146 to -27 for GRA6. Quantitative CAT assay and mutation analysis show that repeated motifs (A/TGAGACG) found in either orientation with respect to transcription are critical elements of these defined promoter regions. We have found such sequence elements in the upstream region of other Toxoplasma genes such as Tub1 and within the stretch of 27bp repeats of the SAG1 promoter.

Animals↗
PubMed1996

Induction of cytotoxic T-cell activity by the protective antigen of Schistosoma mansoni Sm28GST or its derived C-terminal lipopeptide.

In a previous work the authors demonstrated that immunization with Schistosoma mansoni 28-kDa glutathione-S-transferase (Sm28GST) was able to reduce hepatic damage in infected mice and that the adoptive transfer of Sm28GST-specific T cells reproduced the protective effect obtained with the recombinant molecule. In the present paper, the authors show that Sm28GST is also able to stimulate an antigen-specific, cytotoxic T-cell response against Sm28GST-pulsed P815 target cells in normal mice and that effector cells induced in vivo were classical Class I MHC-restricted CD8+ lymphocytes. The authors found no spontaneous CTL activity against Sm28GST-pulsed target cells during the course of the infection by S. mansoni although Sm28GST is expressed at different developmental stages of the parasite. It was observed, however, that immunization with Sm28GST is sufficient to elicit a significant level of CTL response for 6 weeks in infected mice. The role of these Class I MHC-restricted CD8+ lymphocytes in the protection observed precisely at the same period in immunized mice remains to be elucidated. The authors also observe that immunization with the lipopeptide form of the C-terminal peptide of the molecule (190-211 peptide) led to a CTL activation comparable to that observed after immunization with the whole molecule demonstrating the feasibility of using a synthetic lipopeptide as immunogen for a CTL response against Sm28GST epitopes. Moreover, like Sm28GST-specific CTLs, 190-211 lipopeptide-specific cells were also Class I MHC-restricted lymphocytes.

Amino Acid Sequence↗
PubMed1996

Immunoglobulin A response in murine schistosomiasis: stimulatory role of egg antigens.

The immunoglobulin G (IgG) and IgA antibody responses to different Schistosoma mansoni antigens have been determined in chronically infected mice as well as in unisexually infected animals. With a panel of enzyme-linked immunosorbent assays (ELISAs), soluble antigens from furcocercariae, adult worms, and eggs were probed with sera collected at 3-week intervals. Bisexually infected animals developed significant IgG and IgA antibody responses to the antigens tested, which increased after egg deposition. In unisexual infections no significant differences were recorded in the IgG antibody profile for furocercaria and adult worm antigens, whereas the IgA antibody response was impaired. Both the IgA and IgG antibody responses toward egg antigens were reduced compared with those in a bisexual infection. Furthermore, a specific mucosal IgA antibody response was observed only in the bisexually infected animals. Histological analysis performed on bisexually infected mice led to the observation of eggs and granulomatous lesions within the Peyer's patch follicles, which are essential sites for the induction of mucosal immunity in the intestine. These data suggest a relationship between egg deposition and the induction of the IgA antibody response toward schistosomes.

Animals↗
PubMed1996

Induction by interferons of human eosinophil apoptosis and regulation by interleukin-3, granulocyte/macrophage-colony stimulating factor and interleukin-5.

The effects of recombinant human interferon alpha (rhIFN-alpha) and interferon gamma (rhIFN-gamma) were examined on the apoptosis of human cord blood derived eosinophils, obtained after 4 weeks of culture with recombinant human interleukin-3 (rhIL-3), granulocyte-macrophage-colony stimulating factor (rhGM-CSF) and interleukin-5 (rhIL-5). Eosinophil viability decreased remarkably after 1 week culture with rhIFN-alpha and rhIFN-gamma. Recombinant rhIFN-alpha also decreased the viability of co-existing monocytes/macrophages, whereas in contrast, rhIFN-gamma increased the percentage of viable monocytes/macrophages. There was no synergistic or additional effect of rhIFN-alpha and rhIFN-gamma on eosinophil viability. Apoptotic eosinophils, detected by their morphological characteristics, or by DNA nick end labeling in situ, increased remarkably after incubation with rhIFN-alpha and increased to a lesser extent with rhIFN-gamma. The numbers of eosinophil-phagocytosing macrophages increased after culture with rhIFN-alpha and also with rhIFN-gamma. In contrast, eosinophilopoietic cytokines such as rhIL-3, rhIL-5 and specially rhGM-CSF, significantly increased eosinophil viability, and partially rescued the effects of rhIFNs. They also decreased apoptotic eosinophil numbers and eosinophil-phagocytosing macrophage numbers. These results indicate that eosinophil viability, at least in vitro, can be differentially regulated by cytokines produced during the immune response.

Apoptosis↗
PubMed1996

[Value of hepatosplenic ultrasonography in the surveillance of Schistosoma mansoni endemics (a study conducted in the Richard Toll region of Senegal)].

Abdominal ultrasound is a reliable and reproducible technique for monitoring the progression of hepatosplenic schistomiasis. It was used in the framework of the @Hope" program against endemic Schistosoma mansoni in the Senegal River region. A total of 166 patients presenting Schistosoma mansoni eggs in stools were divided into age groups with a sex ratio of 1. All patients underwent the same ultrasound examination including measurement of the liver and assessment of the branches of the portal vein system. Our findings indicated that highly sensitive hypertrophy of the left lobe of the liver occurs early since this feature was observed in all patients over the age of 15 years. Alterations of the portal system were observed in 73% of patients but were moderate, stage 1, in the zone where incidence of positive stools is over 90%. Grade III lesions were only found in patients over 23 years of age. Although these lesions accounted for 4% of the cases, this finding underscores the need for surveillance in a region where infestation became endemic less then ten years ago raising fears that severe schistosomal portal hypertension would become widespread. A mobile ultrasonographic surveillance unit would be useful in the region.

Adolescent↗
PubMed1996

[Analysis of peptides associated with class II MHC molecules, HLA-DR3: implication for the prediction of peptides useful for vaccines].

In order to characterize peptide binding motifs of MHC class II molecules HLA-DR3, we have sequenced pool or single peptides eluted from the binding groove. Anchor residues identified are in agreement with peptide binding and sequencing studies reported by different groups. Four positions seem to be dominant (i, i + 3, i + 5, i + 8) while 2 secondary positions (i + 1, i + 2) could cooperate to facilitate binding. According to all the criteria define here and the literature, we propose an anchor motif specific for DR3, which has been tested on the sequence of an antigen from Schistosoma mansoni. Three out of 6 putative epitopes identified share common sequences with immunodominant regions determined in humans and by experimental immunizations in animal models. Extended to other alleles, this approach could be suitable to define potentially immunodominant peptides useful for vaccines.

Amino Acid Sequence↗
PubMed1995

Human eosinophils express a receptor for secretory component. Role in secretory IgA-dependent activation.

The existence of a functional receptor for secretory component (SC) on the eosinophil membrane might explain the preferential degranulation induced by secretory IgA (sIgA) when compared to serum IgA. Indeed, flow cytometry analysis revealed that purified human SC could bind to a subpopulation (4-59%) of blood eosinophils purified from 19 patients with eosinophilia. Binding of radiolabeled human SC could be competitively inhibited using unlabeled SC or secretory IgA but not with serum IgA or IgG. Immunoprecipitation and immunosorbent chromatography using human SC revealed the presence of a major component at 15 kDa in eosinophil extracts as well as in culture supernatants but not in neutrophils. The 15-kDa protein eluted from the human SC immunosorbent was able to bind to SC or to sIgA but not to serum IgA. Eosinophils preincubated with human SC or sIgA released eosinophil cationic protein (ECP) and eosinophil peroxidase (EPO) after addition of anti-SC or anti-IgA monoclonal antibody as respective cross-linking reagents. These results indicated that binding of free or complexed SC to human eosinophils could induce eosinophil degranulation. Furthermore, the dose-dependent inhibition by SC of mediator release induced by sIgA but not by serum IgA, suggested that the receptor for SC could be involved in the preferential degranulation mediated by sIgA. These results indicate a novel pathway of eosinophil activation and its potential involvement in mucosal immunity, particularly in inflammatory diseases associated with infiltration of eosinophils and the enhanced production of sIgA.

Binding, Competitive↗
PubMed1995

Schistosoma mansoni: interaction of nuclear extracts with the CCAAT-binding site revealed by the gel shift assay.

Analysis of the 5'-flanking region of the gene encoding the 28-kDa glutathione S-transferase of Schistosoma mansoni (Sm28GST) indicated the presence of motifs identical to AP-1 and CCAAT-family transcription factor recognition sequences. Gel retardation experiments showed that nuclear extracts from adult S. mansoni bound to an oligodeoxynucleotide containing at CCAAT box. A DNA fragment corresponding to the region of Sm28GST containing the CCAAT motif was demonstrated to interact with schistosome nuclear proteins. This binding was dependent on the presence of the CCAAT pentanucleotide motif. Nuclear factor Y (NF-Y) is a member of the CCAAT transcription factor family that has absolute requirement for the CCAAT sequence and that is highly conserved throughout evolution. The results of a PCR-based strategy aimed at cloning the NF-YA protein of S. mansoni are presented.

Amino Acid Sequence↗
PubMed1995

Schistosoma mansoni: the presence and potential use of opiate-like substances.

The present study demonstrates that morphine- and codeine-like molecules are present in Schistosoma mansoni following HPLC separation and identification with an appropriate commercially available antibody. Furthermore, the endogenous material, corresponding to morphine, mimics authentic morphine in its ability to induce immunocyte rounding and immobility, an action that is naloxone sensitive. The codeine-like material is not found at high concentrations compared to the morphine-like material, indicating, as in mammals and Mytilus edulis, the potential rapid conversion of codeine to morphine. Coincubation with human leukocytes increases the endogenous level of this material in adult worms, indicating the presence of a positive feedback loop. Last, EDTA, a chelator of divalent cations, has a strong stimulating effect in the synthesis of morphine-like material by the worm as noted by higher levels of this material in its presence. Taken together, the results suggest that this parasite may utilize this immune downregulating molecule in its effort to escape host immunosurveillance as well as in inhibiting an immune response directed against itself.

Analgesics, Opioid↗
PubMed1995

Characterization of a dense granule antigen of Toxoplasma gondii (GRA6) associated to the network of the parasitophorous vacuole.

This work describes the molecular characterization of GRA6, a novel Toxoplasma gondii dense granule antigen of 32 kDa. cDNA clones encoding this protein were isolated using a rat serum directed against an HPLC fraction enriched in the protein GRA5. Cross-reactivity between GRA5 and GRA6 was demonstrated by production of sera against the recombinant GRA5 protein. A serum against a recombinant fragment of GRA6 which does not react with GRA5 allowed the localization of this antigen at the subcellular level. GRA6 is detected in the dense granules of tachyzoites, and in the parasitophorous vacuole, closely associated to the network. The gene encoding GRA6 and its flanking regions were completely sequenced from cDNA and genomic inserts. Primer extension experiments demonstrated that the cap site of the GRA6 gene was located 37 bp upstream of the 5' end of the longest cDNA insert (1600 bp). The GRA6 gene potentially encodes a 230-amino-acid polypeptide, does not contain any introns and seems to be present as a single copy in the genome of T. gondii. The deduced polypeptide contains two hydrophobic regions with the characteristics of transmembrane domains. The N-terminal domain does not fit the classical feature of a signal peptide. The central hydrophobic domain is flanked by two hydrophilic domains which contain four blocks of amino acids homologous to the GRA5 protein. The C-terminal hydrophilic region comprises 24% of glycine residues, which may indicate a structural role for GRA6 in the network.

Amino Acid Sequence↗
PubMed1995

Transcriptional regulation of Schistosoma mansoni calreticulin: possible role of AP-1.

Little is known about the regulation and control of Schistosoma mansoni gene expression. In order to study such mechanisms a gene reporter expression vector construction, under the control of a promoter region derived from the S. mansoni calreticulin gene was used to transfect the human Jurkat T cell line. The promoter region contains potential TATA and CAAT boxes as well as an AP-1 core element. We show here that transcriptional factors of eucaryotic cells may induce a gene reporter activity under the control of a S. mansoni promoter region. Treatment of stably transfected cells with N-acetyl cysteine (NAC), a well-characterized antioxidant which counteracts the effects of reactive oxygen intermediates, enhanced the AP-1 dependent transactivation. This effect was abolished when the SmCaR promoter region was deleted in the AP-1 site. Electrophoretic Mobility Shift Assays showed that the AP-1 sequence of S. mansoni bound to both S. mansoni extracts and in nuclear extracts from Jurkat cells, thus explaining possible activation of AP-1 by NAC. Finally treatment of S. mansoni schistosomula and adult worms with NAC induced an increased synthesis of calreticulin protein suggesting a possible role of redox mechanisms in the regulation of a calreticulin gene transcription process in S. mansoni.

Acetylcysteine↗
PubMed1995

Eosinophils: from low- to high-affinity immunoglobulin E receptors.

Several experimental approaches have been used to identify immunoglobulin (IgE) binding molecules expressed by human eosinophils. After the description that Fc epsilon RII/CD23 identified on eosinophils could participate in IgE binding and IgE-mediated cytotoxicity, Mac2/epsilon binding proteins belonging to the S-type lectin family were also detected on human eosinophils. Anti-Mac2 monoclonal antibodies inhibited eosinophil-dependent cytotoxicity towards parasitic targets. More recently, Fc epsilon RI was demonstrated on human eosinophils from hypereosinophilic patients. The 3 components of Fc epsilon RI, alpha, beta and gamma chains, were detected in eosinophils. The alpha chain of Fc epsilon RI was shown to be involved in IgE binding to eosinophils and in the selective release of eosinophil peroxidase. The participation of Fc epsilon RI-bearing eosinophils in a protective immune response against a parasitic infection indicates a so far unsuspected function of Fc epsilon RI. The interactions between the different types of IgE binding molecules are discussed.

Antigens, Differentiation↗
PubMed1995

Analysis of the Mycobacterium tuberculosis 85A antigen promoter region.

A mycobacterial expression-secretion vector was constructed in which the Escherichia coli alkaline phosphatase (phoA) reporter gene was placed under the control of the Mycobacterium tuberculosis 85A promoter and secretion signal sequences. In recombinant Mycobacterium smegmatis and Mycobacterium bovis BCG, PhoA activity could readily be detected on the mycobacterial cell surface and in the culture supernatant, indicating that the 85A signals can drive heterologous expression and secretion in both species. In contrast to the mycobacteria, the 85A promoter did not function in E. coli. We mapped the promoter region by progressive deletions using BAL 31 exonuclease and by primer extension analysis. Insertion and deletion mutations within the promoter region indicated that, unlike most E. coli promoters but similar to Streptomyces promoters, the position of the putative -35 region was not critical for efficient promoter activity. In addition, we investigated the ability of the identified signals to drive the production and secretion in BCG of recombinant Schistosoma mansoni glutathione S-transferase (Sm28GST), a protective antigen against schistosomiasis. BALB/c mice immunized with the recombinant BCG by a single dose exhibited a weak but specific T-cell response to Sm28GST.

Alkaline Phosphatase↗