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M Gui

Publications and source records attributed to M Gui.

15 recordsLinked to original sources
PubMed2000

Structural requirements for antigen presentation by mouse CD1.

The structural basis for the T cell response to glycolipid antigens (Ags) remains poorly understood. T lymphocytes autoreactive for mouse CD1 (mCD1.1) or reactive for the glycosphingolipid alphagalactosylceramide (alpha-GalCer) presented by mCD1.1 have been described previously. In this paper it is shown that mutations at the top of the alpha helices and in the bottom of the Ag-binding groove can disrupt both mCD1.1 autoreactivity and alpha-GalCer recognition. The locations of the positions that affect T cell responses indicate that recognition of mCD1.1 is not likely to be unconventional or superantigen-like. Furthermore, the effects of the bottom of the pocket mutation suggest that the autoreactive response could require an autologous ligand, and they indicate that alpha-GalCer binds to the groove of mCD1.1, most likely with the shorter 18-carbon hydrophobic chain in the A' pocket. Natural killer T cell hybridomas with identical T cell antigen receptor (TCR) alpha chains and different beta chains respond differently to alpha-GalCer presented by mCD1.1 mutants. This finding indicates a role for TCR beta in defining natural killer T cell specificity, despite the more restricted diversity of the alpha chains in these cells. Overall, the data are consistent with a mode of lipoglycan recognition similar to that proposed for glycopeptides, in which the TCR alpha and beta chains survey a surface composed of both mCD1.1 and the carbohydrate portion of alpha-GalCer.

Amino Acid Substitution↗
PubMed2000

B-cell commitment, development and selection.

Here we review three areas in B-cell development in the mouse, with a focus on relevance to B-1/CD5+ B cells. Multiparameter flow cytometry has allowed the dissection of intermediate stages of developing B cells, both in fetal liver and bone marrow. In the first area, we present recent work that has delineated a fraction of pre-pro-B cells, committed to the B lineage, but lacking any immunoglobulin rearrangements. Next, the role of the pre-B-cell receptor in B-cell repertoire selection has become clear in the past few years, but we present work suggesting that the action of this process during fetal life is different, resulting in selection of a very distinct repertoire compared with adult. Finally, we describe a new VH3609 antithymocyte Ig transgenic mouse model system that has provided the first definitive evidence for the role of self-antigen in development and maintenance of natural autoreactive B cells.

Animals↗
PubMed1999

Peripheral CD4+ T cell maturation recognized by increased expression of Thy-1/CD90 bearing the 6C10 carbohydrate epitope.

The SM6C10 IgM autoantibody recognizes a surface determinant, 6C10, that is highly expressed on all immature thymocytes. In contrast, its expression on peripheral T cells appears developmentally regulated, i.e., absent from most naive T cells in spleen of neonatal mice, but expressed on 40-80% of naive CD4+ T cells in adult. In this paper, we demonstrate that SM6C10 recognizes a carbohydrate epitope on the Thy-1 glycoprotein using immunoprecipitation analysis, by binding to affinity-purified Thy-1 in an ELISA, and by sensitivity to N-glycosidase-F treatment. Retroviral Thy-1 gene transduction experiments into Thy-1- variant T cell lines and a pro-B cell line provide evidence that 6C10 glycosylated Thy-1 expression is not restricted to T cells but depends on the recipient cell. Therefore, differences in 6C10 levels among Thy-1+ T cells in mice likely reflect developmental regulation of posttranslational modification of the Thy-1 glycoprotein. The ability of naive CD4+ T cells to respond to anti-Thy-1 stimulation increases from neonate to adult, and 6C10- naive cells from adult mice respond poorly compared with 6C10+ cells, similar to the cells in neonatal mice. These results suggest that there is functional maturation by peripheral CD4+ T cells that coincides with 6C10 glycosylated Thy-1 up-regulation, and natural autoantibody recognizes this 6C10 carbohydrate epitope.

Animals↗
PubMed1999

Positive selection of natural autoreactive B cells.

Lymphocyte development is critically influenced by self-antigens. T cells are subject to both positive and negative selection, depending on their degree of self-reactivity. Although B cells are subject to negative selection, it has been difficult to test whether self-antigen plays any positive role in B cell development. A murine model system of naturally generated autoreactive B cells with a germ line gene-encoded specificity for the Thy-1 (CD90) glycoprotein was developed, in which the presence of self-antigen promotes B cell accumulation and serum autoantibody secretion. Thus, B cells can be subject to positive selection, generated, and maintained on the basis of their autoreactivity.

Aging↗
PubMed1998

Selective ability of mouse CD1 to present glycolipids: alpha-galactosylceramide specifically stimulates V alpha 14+ NK T lymphocytes.

Mouse CD1 (mCD1) glycoproteins are known to present peptides, while human CD1 molecules present glycolipids. In mice, mCD1-autoreactive NK T cells play critical roles in various immune responses, through the secretion of high amounts of cytokines. This study was initiated to determine whether glycolipids are involved in the autorecognition of mCD1 by NK T cells. Alpha-galactosylceramide (alpha-GalCer) was the only glycolipid tested capable of eliciting an mCD1-restricted response by splenic T cells. Moreover, splenic T cells derived from mCD1-deficient mice were not stimulated by alpha-GalCer, suggesting that the responsive T cells are selected by mCD1. Using cytoflow techniques, we confirmed that, in response to alpha-GalCer, IFN-gamma-secreting cells displayed an NK T cell phenotype. The predominance of IFN-gamma vs IL-4, however, is determined by the type of mCD1+ APC, suggesting the potential for APC regulation of cytokine production by NK T cells. Among a panel of 10 mCD1-autoreactive T cell hybridomas, only the ones that express the typical V alpha 14 J alpha 281 TCR rearrangement of NK T cells responded to alpha-GalCer. Fixation or treatment of mCD1+ APCs with an inhibitor of endosomal acidification and the use of mCD1 mutants unable to traffic through endosome still allowed alpha-GalCer to stimulate NK T cells. Thus, endosomal trafficking and Ag processing are not required for glycolipid recognition. In summary, alpha-GalCer might be the autologous ligand, or a mimic of a glycolipid ligand, involved in the mCD1-mediated stimulation of NK T cells.

Animals↗
PubMed1995

Inhibition of human glutathione reductase by S-nitrosoglutathione.

S-Nitrosoglutathione (GSNO) represents a major transport form in nitric oxide (NO) in biological systems. Since NO and GSNO have been shown to modulate the function of various proteins, we studied the influence of GSNO and other NO donors on human glutathione reductase (GR). Catalyzing the reaction NADPH+GSSG+H(+)-->NADP(+) + 2 GSH, the dimeric flavoprotein GR is the central enzyme of the glutathione redox metabolism. GSNO was found to inhibit crystalline erythrocyte GR in two ways: (a) as a reversible inhibitor GSNO is competitive with glutathione disulfide (GSSG), the Ki being appr. 0.5 mM; (b) as an irreversible inhibitor; after 1 h (3 h) incubation with 1 mM GSNO, GR (2.5 U/ml, representing intraerythrocytic concentrations) was inhibited by 70% (90%). This inhibition depended on the presence of NADPH and could not be reversed by dilution nor by reducing agents. Absorption spectra indicate that the charge-transfer interaction between Cys63 and the flavin is abolished by this modification. In a GR sample inhibited by 90% with GSNO, the Km values for the substrates GSSG and NADPH were not significantly changed nor did the modification induce oxidase activity of the enzyme. GSNO was found not to be a substrate in the forward reaction of GR. This implies that GSNO is not accounted for by methods which employ GR for determining total glutathione. Incubating isolated GR for 60 min with other NO donors, namely 1 mM sodium nitroprusside or 1 mM S-nitroso-N-acetyl-DL-penicillamine (SNAP), resulted in only 25% and 10% inhibition, respectively. This attests to a specific affinity of GSNO to the enzyme. GSNO inhibition patterns comparable to purified authentic GR were obtained for purified recombinant GR, a GR mutant lacking the 15 N-terminal amino acids including Cys2, and for the enzyme present in diluted fresh haemolysates (0.02 U/ml); in concentrated haemolysates the inhibition was less pronounced. GR of intact erythrocytes was not affected when exposed to GSNO in the medium. Our results suggest that the irreversible inhibition of GR by GSNO involves nitrosylation of Cys63 and/or Cys58 at the catalytic site of the enzyme. To further investigate the mechanism of inactivation we have crystallized GSNO-modified GR for X-ray diffraction analysis.

Binding Sites↗
PubMed1995

Schistosoma japonicum and S. mansoni: comparison of larval migration patterns in mice.

Mice were infected percutaneously with cercariae of Schistosoma japonicum or S. mansoni and parasites recovered by tissue-mincing from the skin or lungs or by perfusion of the mesenteric veins. S. japonicum had a narrow peak of recovery (up to 30%) from the lungs 3 days after infection, whereas lung recovery of S. mansoni peaked only on day 6 and levelled off during the following week. Infection with S. japonicum induced lung petechiae, but only after most of the parasites had left the lungs. The axillary lymph nodes draining the infection site increased in weight after infection and this effect was much greater and longer with S. mansoni than with S. japonicum. S. japonicum was perfusable from the mesenteric veins earlier (from day 3 onwards) and in higher number (40-60% from days 6 to 10) than S. mansoni (20% on day 20). The percentage of cercariae developing to adult worms was 57% for S. japonicum and 33% for S. mansoni. The data demonstrate that S. japonicum might escape from local tissue reactions in the skin and lungs and, due to its rapid migration, might induce only poor lymphocyte proliferation. As a possible consequence, S. japonicum may establish more efficiently in mice than S. mansoni.

Animals↗
PubMed1995

Comparative phenotypic analysis of lymph node cells in mice after infection or vaccination with normal or ultraviolet-attenuated cercariae of Schistosoma japonicum or S. mansoni.

Mice were infected with 200 untreated or vaccinated with 500 ultraviolet-attenuated cercariae of either Schistosoma japonicum or S. mansoni. For three weeks, cell numbers in axillary and mediastinal lymphnodes were counted and cell populations typed by cytofluorometry. In the axillary lymphnodes, numbers of B-cells and CD3+CD4+ T-cells but not CD3+CD8+ T-cells increased. Following vaccination with either species, parasite migration was apparently delayed in the skin and interrupted at the lungs, the lymphnodes gained weight, and cell numbers of axillary lymph nodes increased more than after infection. In mediastinal lymphnodes, only immunization with S. japonicum but not S. mansoni cercariae led to an increase of CD3+CD4+ T-cells. Following infection, both schistosome species induced higher CD3+CD4+, but not CD3+CD8+ T-cells in mediastinal nodes, and the peak was earlier with S. japonicum (about seven days after infection) than with S. mansoni (about 10 days). In analogy to T-cell observations by others using a gamma-attenuated cercarial vaccine in S. mansoni, the present results suggest that CD3+CD4+ cells also play a role in the ultraviolet-attenuated vaccine against S. japonicum.

Animals↗
PubMed1994

Redox processes in malaria and other parasitic diseases. Determination of intracellular glutathione.

The role of oxidative stress resulting from production of reactive oxygen species and/or from suppression of the cellular antioxidant capacity in parasitic infections is shortly reviewed. The experimental part of the paper deals with the glutathione (GSH)--glutathione reductase (GR) system, a cornerstone of intracellular antioxidant defence mechanisms. For studying this system in parasitic diseases such as malaria new or modified methods are required. Total glutathione comprising GSH and glutathione disulphide (GSSG) in blood samples was assayed as follows. One volume of blood (> or = 10 microliters) is mixed with two volumes of 5% sulphosalicylic acid; after centrifugation (5 min, 10000 g), 10 microliters of supernatant is taken for spectrophotometric analysis using the 5,5'-dithiobis(2-nitrobenzoate) (DTNB)-glutathione recycling assay. When compared with the original method, the procedure reported here is more sensitive, less time-consuming, avoids unfavourable pH-values and leads to a sample which when frozen is stable for months. In a pilot study, the method was applied to 14 patients suffering from malaria caused by Plasmodium falciparum. The concentrations of erythrocyte glutathione were significantly decreased in the patients (1.42 +/- 0.47 mM, mean +/- SD) when compared to age- and sex-matched controls (2.11 +/- 0.45 mM, P < 0.01). The findings are contrasted with P. falciparum cultures in vitro where glutathione levels are known to be elevated. Based on the characteristics of GR a concept of determining the redox state of single cells is introduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Reactivity of Schistosoma japonicum and S. mansoni antigen preparations in indirect haemagglutination (IHA) with sera of patients with homologous and heterologous schistosomiasis.

Sera of patients infected with Schistosoma japonicum, S. mansoni or S. haematobium were tested in an indirect haemagglutination assay (IHA) using soluble S. japonicum egg antigen (SjSEA) and soluble S. mansoni adult antigen prepared either from a Puerto Rican strain (SmAWA) or an Egyptian strain (SmBW; Cellognost-Schistosomiasis Kit). Reactions were best, in terms of titres and sensitivity, in homologous systems. Heterologous systems were less reliable, particularly those using sera from urinary schistosomiasis patients. It is suggested that IHA is a suitable test to detect Schistosoma infections, especially when homologous systems are used.

Animals↗
PubMed1991

Miracidia of Schistosoma japonicum: approach and attachment to the snail host.

Schistosoma japonicum miracidia swim directed along a chemical gradient toward the snails Oncomelania hupensis and Biomphalaria glabrata, and they turn back when the concentration of attractive chemicals decreases. The host signal for this chemotactic response has a molecular weight of more than 30,000. When swimming miracidia encounter the surface of O. hupensis or agar containing O. hupensis snail-conditioned water (SCW) they perform the host-specific responses "contact with return," "repeated investigation," and "attachment," but they do not exhibit such behavior when encountering B. glabrata surface or agar containing B. glabrata SCW. Thus S. japonicum miracidia respond to different host signals when they approach snails than when they attach to snails.

Animals↗