Search PubMed⌕ Search

Biomedical subjects

O Garraud

Publications and source records attributed to O Garraud.

At least 37 records · Page 2Linked to original sources
PubMed1999

Flow cytometric analysis of IgG reactive to parasitized red blood cell membrane antigens in Plasmodium falciparum-immune individuals.

Antigens exposed at the surface of Plasmodium falciparum parasitized red blood cells (pRBCs) represent potential targets for protective antibodies involved in opsonization and immune phagocytosis of pRBCs. We measured the recognition of parasitized red blood cell membrane associated antigens by IgG in the plasma of clinically immune individuals by flow cytometry and ELISA. The plasmas were selected on the basis of preexisting IgG antibodies to pRBC membrane associated recombinant proteins. In every plasma sample IgG could bind the surface of live pRBCs in flow cytometry. In addition, there was a significant correlation between the level of IgG recognition of live pRBCs and of pRBC membrane ghost proteins or major identified antigens by ELISA. Flow cytometry thus represents a technique suitable to test for the accessibility and potential functionality of IgG antibodies directed to antigens expressed by the surface of pRBCs.

Adolescent↗
PubMed1999

Immune responses to P. falciparum-MSP1 antigen: lack of correlation between antibody responses and the capacity of peripheral cellular immune effectors to respond to this antigen in vitro.

Protective immunity to P. falciparum blood stage infection is thought to be dependent on IgG antibodies, although the mechanisms that underlie such immunity are not clearly understood. One of the antigens thought to be involved in this protective response is MSP1. The present study has examined the levels and distribution of IgG (and IgM) antibodies to the C-terminal 19 kDa fragment of MSP1 in plasma from P. falciparum immune adult Senegalese and the capacity of the peripheral blood mononuclear cells from these patients to either proliferate or secrete IFN-gamma, IL-10 or IL-4 in vitro in response to this antigen. Specific antibodies were found in 74% of individuals' plasma; 44% of mononuclear cells proved capable of proliferating in vitro and IFN-gamma, IL-10 and IL-4 were detected in 37, 23 and 0% of culture supernatants, respectively. No significant association was found between the presence of antibodies and immune cell reactivity under the culture conditions used. This study emphasizes the complexity of the mechanisms responsible for the sustained production of potentially protective antibodies in response to proposed T-cell dependent P. falciparum blood stage antigens.

Adult↗
PubMed1999

Regulation of immunoglobulin production in hyper-IgE (Job's) syndrome.

BACKGROUND: The hyper-IgE (HIE), or Job's, syndrome is a rare, complex disorder characterized by high levels of serum IgE in childhood and chronic dermatitis with recurrent, often severe sinopulmonary and skin infections. Although the etiology of HIE syndrome is unknown, there is evidence that patients with HIE have abnormalities in cellular immune responses, as well as in the production of polyclonal and antigen-specific antibodies. Furthermore, there appears to be a common (but still undefined) mechanism underlying the regulation of IgE and IgG4 in this condition. OBJECTIVE: We sought to assess the role of cytokines or cytokine receptor blockade in regulating IgE and IgG4 production in HIE. METHODS: PBMCs were isolated from patients with HIE (n = 9) and normal individuals (n = 8), and IgE and IgG4 production was assessed spontaneously, in the presence of recombinant IL-4, IL-13, IL-6, IL-8, IL-12, and IFN-gamma, under conditions in which the IL-4R was blocked or when these cytokines were neutralized by specific monoclonal or polyclonal antibodies. RESULTS: In PBMCs from patients with HIE, a significant (P <.01) reduction in the spontaneously produced IgE (and IgG4) was induced by either IFN-gamma or IL-12, although neither cytokine could totally abrogate the immunoglobulin production. Whereas spontaneous IgE (and IgG4) production was not affected by exogenous IL-4 and IL-13, neutralizing antibodies to IL-4 and IL-13 also significantly (P <.01) reduced the production of IgE and IgG4, a finding supported by the observation of increased expression of IgE germline transcripts in these patients. In contrast to the neutralization of IL-4 and IL-13 protein, anti-IL-4R antibodies or soluble IL-4R completely suppressed IgE and IgG4 production in HIE. Similarly, IL-8 or antibodies to IL-6 and TNF-alpha, cytokines known to affect IL-4-dependent IgE production, completely inhibited both IgE and IgG4 production. CONCLUSION: These data show that overproduction of IgE and IgG4 can be regulated by a number of cytokines affecting the IL-4-dependent pathway of IgE/IgG4 production in HIE and suggest new targets for therapeutic intervention.

Cytokines↗
PubMed1999

Secretion of parasite-specific immunoglobulin G by purified blood B lymphocytes from immune individuals after in vitro stimulation with recombinant Plasmodium falciparum merozoite surface protein-119 antigen.

The C-terminal 19 000 MW fragment of merozoite surface protein-1 (MSP119) is one of the most promising candidate antigens for a malaria vaccine. Baculovirus recombinant Plasmodium falciparum MSP119 has been used to define conditions for the in vitro production of specific antibodies by purified human blood B cells in a culture system where T-cell signals were provided by the engagement of CD40 molecules and exogenous cytokines. MSP119 preferentially induced surface immunoglobulin G (IgG) -positive (sgamma+) B lymphocytes from P. falciparum-immune donors to differentiate and produce antigen-specific IgG. In contrast, naïve B cells or cells from non-immune donors could not be induced to secrete parasite-specific IgG in vitro. Although IgG secretion was obtained in the absence of exogenous cytokines, it was dependent on B-cell-derived interleukin-10 (IL-10) and/or B-cell factor(s) under the control of IL-10, since IgG levels were significantly decreased in the presence of neutralizing anti-IL-10 antibodies. These results demonstrate at the cellular level that a single malaria vaccine candidate polypeptide can direct parasite-specific antibody production mediated by the secretion of potentiating factors.

Adult↗
PubMed1999

Immune responses to Plasmodium falciparum-merozoite surface protein 1 (MSP1) antigen, II. Induction of parasite-specific immunoglobulin G in unsensitized human B cells after in vitro T-cell priming with MSP119.

A baculovirus recombinant antigen corresponding to the C-terminal 19 000 MW fragment of Plasmodium falciparum merozoite surface protein 1 (MSP119), has been used to prime T cells from individuals with no previous exposure to malaria, to provide help for the induction of a parasite specific antibody response in vitro. Although MSP119 alone could induce a small but detectable T-cell response, which included interleukin-4 (IL-4) secretion, this response was significantly increased by the presence of IL-2. In addition, IL-4 was shown to synergize with IL-2 for the induction of antigen-specific T-cell responses. If interferon-gamma (IFN-gamma), IL-12, or neutralizing anti-IL-4 antibody was present at the time of priming, the T-cell responses were abolished. Parasite-specific immunoglobulin G (IgG) could be detected after secondary restimulation with MSP119, IL-10 and anti-CD40 monoclonal antibody in cultures containing MSP119 primed T cells, autologous B cells, IL-2 and IL-4. No antibody was secreted in the absence of primed T cells in this B-cell culture assay. These data show that recombinant MSP119, a leading malaria vaccine candidate, can prime non-immune human lymphocytes under defined in vitro experimental conditions, which include regulatory cytokines and/or other costimulatory molecules. This is a complementary approach for exploring immunogenic mechanisms of potential vaccine candidates such as P. falciparum antigens in humans.

Animals↗
PubMed1999

Different Plasmodium falciparum recombinant MSP1(19) antigens differ in their capacities to stimulate in vitro peripheral blood T lymphocytes in individuals from various endemic areas.

This study reports on T-cell proliferative responses to the 19-kDa C-terminal domain of the Plasmodium falciparum merozoite surface protein (MSP1(19)). Three different recombinant proteins were used: an Escherichia coli product expressing the first EGF-like domain and Saccharomyces cerevisiae and baculovirus/insect-cell-produced proteins containing both EGF-like domains, the latter protein being produced with or without N-glycosylation. Cell donors were P. falciparum-immune adults with no recent history of clinical malaria and recruited from three Senegalese settings with different epidemiological parasite transmission. Each mononuclear-blood-cell preparation was stimulated with a range of concentrations of the three proteins. Most subjects' mononuclear cells were reactive to at least one protein, but significant differences in lymphoproliferation were seen between the settings and within individual cultures depending on the protein source and concentration. Importantly, lymphoproliferation indices correlated inversely with the intensity of P. falciparum malaria transmission. When purified T lymphocytes were cultured in the presence of MSP1(19) plus autologous monocytes, B lymphocytes or a proposed CD1+ dendritic-cell population as costimulatory cells, significant differences were observed depending on the individual's previous exposure to parasites. This study shows that the stimulation of lymphocyte proliferation in vitro with MSP1(19) depends on several factors, including epidemiological conditions and protein preparations.

Adult↗
PubMed1999

Quantitative computer image analysis of chondroitin sulfate A expression in placentas infected with Plasmodium falciparum.

Most pathological conditions resulting from infection with the human malaria parasite Plasmodium falciparum occur as a consequence of the sequestration by several adhesion molecules of parasite-infected red blood cells (IRBCs). Recent reports have provided evidence that placental vascular endothelial ligands for IRBCs were mostly restricted to chondroitin sulfate A (CSA). The expression of CSA in malaria-infected placentas was investigated in a prospective case-control study in a hypoendemic area (Dakar, Senegal). The tissue distribution of CSA was measured in the terminal villi by immunostaining combined with image processing in 20 infected and 20 noninfected frozen sections of placenta. The villous surface immunostained by anti-CSA antibody was higher in infected than in noninfected placentas (p<0.03), in placentas with active infection than in those with past chronic infection (p<0.05), and in infected placentas with positive imprints than in those with negative imprints (not significant; p=0.06). Labeling was found in the extracellular matrix and in endothelial and stromal cells of all the placentas. Syncytiotrophoblast immunostaining was detected in all placentas associated with active or active chronic infection (n=7) but in only 4/13 placentas with past chronic infection (p<0.01). The presence of P. falciparum in the imprint was significantly correlated with immunostaining of CSA in syncytiotrophoblasts (p=0.003). These results suggest that CSA can play an important role in the sequestration of P. falciparum in human placentas during the acute phase of infection.

Animals↗
PubMed1999

[Antibodies specific to Plasmodium falciparum antigens in immune individuals: III. Seasonal course of the response to a major antigen of the asexual blood forms in two sites of different malaria exposure].

Specific IgG1 and IgG3 antibody responses to a major Plasmodium falciparum blood stage antigen i.e. MSP1 have been measured in plasma obtained from immune individuals living in areas with different endemicities and sampled at different periods corresponding to different levels of parasite transmission. The study shows a significant imbalance between IgG1 and IgG3 antibody responses in Dielmo vs. Ndiop, and a differential regulation of IgG1 and IgG3 responses both in subclasses and in titers (low: 1/200, and high: 1/2,000) depending upon intensity of parasite exposure.

Animals↗
PubMed1998

Imbalanced distribution of IgM and IgG antibodies against Plasmodium falciparum antigens and merozoite surface protein-1 (MSP1) in pregnancy.

In malaria endemic areas, pregnancy is assumed to be associated with a specific reduction in immunity to Plasmodium falciparum malaria. To understand some of the mechanisms which underlie such a poor immunity, we have attempted to examine the frequency and distribution of IgM and IgG antibodies to a crude antigenic extract of parasitized erythrocytes and to the merozoite surface protein-1 (MSP1), in a population of mothers compared to control non-pregnant women, all living in Dakar and suburbs. Specifically, this work describes: (i) the responses of mothers and control women; (ii) the balance between IgM and IgG responses; and (iii) responses to malarial antigen and to MSP1. An unexpected balance between P. falciparum-specific IgM and IgG is shown, associated with a substantial increase in anti-MSP1 IgM, and a decrease in anti-MSP1 IgG in parturients.

Animals↗
PubMed1997

Induction of parasite antigen-specific antibody responses in unsensitized human B cells is dependent on the presence of cytokines after T cell priming.

Using two recombinant filarial protein Ags and keyhole limpet hemocyanin, we sensitized T cells from uninfected, nonatopic individuals in such a manner that they were able to provide help for the selective induction of an Ag-specific Ab response. IL-2 and IL-4 were shown to be critical for sensitizing the T cells; once sensitized, these T cells could provide the necessary signals for B cells to produce Ag-specific Abs, provided that IL-4 (or IL-2) was supplied exogenously. Primary exposure of T cells to IFN-gamma, but not to IL-12, prevented the Ag-sensitized T cells from helping B cells to produce specific Abs, apart from the IgG2 isotype. These data suggest that Ab-producing B cells of a defined Ag specificity and isotype can be generated differentially after in vitro priming of human T cells by Ag, providing regulatory cytokines are also present.

Animals↗
PubMed1997

Plasmodium falciparum- and merozoite surface protein 1-specific antibody isotype balance in immune Senegalese adults.

This study shows markedly different isotype distributions of antibodies to asexual blood stages of Plasmodium falciparum and to merozoite surface protein 1 in clinically immune Senegalese adults depending on the study site. The relationships between immunoglobulin M (IgM) and IgG and between IgG3 and IgG1 antibodies differed in settings where transmission is perennial compared to settings where it is seasonal. This suggests a role for antibody class and/or subclass production and utilization in the regulation of protective immunity to such antigens.

Adult↗
PubMed1997

[Specific antibodies against Plasmodium falciparum antigens in immune subjects: I. Comparison of detection/titration methods].

We report a comparative study of specific antibody levels to the blood stages of P. falciparum in individuals living in two different areas with different transmission levels of malaria. We have compared 2 techniques for the detection/titration of antibodies i.e. ELISA and IFI, ELISA being particularly suitable for immuno-epidemiological related studies. A schizont lysate from P. falciparum infected red blood cells from FUP/CB Marburg strain as antigen proved usefullness, as compared with an antigen extracted from a local strain recently adapted to in vitro culture. Using these techniques, high specific antibody responses were found in the villagers' sera and mean levels of antibodies increased with age. Levels of specific IgG were comparable between those two locations, in spite of a ten fold higher level of transmission between the two villages. In contrast, a significantly higher level of IgM in adults living in holoendemic.

Adolescent↗
PubMed1997

[Specific antibodies against Plasmodium falciparum antigens in immune subjects: II. Screening of responses against the merozoite major surface antigen (MSP!)].

Specific immune responses to asexual blood stages of P. falciparum antigens (a lysate of parasitized red blood cells and a characterized vaccine candidate i.e. MSP1 p19) were analyzed in plasma samples from immune adult individuals living in three different areas of Senegal, where malaria transmission is different. Most individuals in the three sites had specific IgG and IgM to total P. falciparum antigens, whereas approximately 50% had either IgG or IgM specific to MSP1 p19. Further, no anti-MSP1 p19 IgG2 and IgG4 antibody was noticed in any individual whereas the distribution of anti-MSP1 p19 IgG1 and IgG3 was different upon the epidemiological context. In addition, no relationship was found between antibody responses and in vitro T cell responses against P. falciparum antigens upon those experimental conditions. These data stress on the relatively elevated distribution of specific antibodies to MSP1 p19 in P. falciparum hyperendemic areas and suggest a differential regulation of isotypes depending on individual parasite exposure.

Adolescent↗
PubMed1996

Differential regulation of antigen-specific IgG4 and IgE antibodies in response to recombinant filarial proteins.

Having identified two recombinant filarial proteins (Ov27 and OvD5B) that induced patient peripheral blood mononuclear cells to produce antigen-specific IgG4/IgE antibodies in vitro, we assessed the role these filarial antigens play in inducing antigen-specific isotype switching (gamma 4 and epsilon) in the absence of T cells. Purified CD19+ s gamma-/s epsilon- B cells were cultured with either of these antigens in the presence of anti-CD40 mAb and human IL-4. Both antigen and polyclonal signals delivered by IL-4 (or IL-13) were necessary for the induction of specific IgG4/IgE antibodies. To assess the role played by cytokines produced by B lymphocytes in antigen-driven selection of the gamma 4 or epsilon isotype, neutralizing anti-cytokine antibodies were used in vitro. While anti-IL-12 antibodies did not alter the antigen-specific IgG4/IgE production, anti-IL-6, anti-IL-13 and anti-tumor necrosis factor-alpha antibodies significantly inhibited the production of IgG4/IgE. Anti-IL-2 and anti-IL-10 antibodies appeared to down-regulate antigen-specific IgG4 antibodies without affecting antigen-specific IgE antibodies. Although anti-CD21 antibodies had no effect on specific IgE antibodies, they up-regulated specific IgG4 antibodies, a finding paralleled by anti-CD23 antibodies. These data suggest that certain filarial antigen-specific IgG4/IgE responses can be differentially regulated and that certain endogenously produced molecules from B cells-such as IL-2, IL-10, CD23 and CD21-play a significant role in the induction of specific isotypes of antigen-specific antibodies.

Animals↗
PubMed1995

Identification of recombinant filarial proteins capable of inducing polyclonal and antigen-specific IgE and IgG4 antibodies.

Filarial infection is characterized by an immune response associated with the production of Ag-specific IgG4 and IgE and IL-4 and IL-5. To identify filarial Ags capable of inducing such responses and to analyze the role Ags themselves play in sustaining it, 24 recombinant filarial parasite proteins were screened for their ability to be recognized by sera from 67 individuals with tissue-invasive filarial infections. Among the recombinant proteins that were recognized by IgG4 or IgE Abs in 25% of the sera or more, two were selected on the basis of their ability to elicit polyclonal and Ag-specific IgE/IgG4 Abs in vitro. Ov27 (analogous to Ov7/cystatin, a cysteine protease inhibitor) and OvD5B (analogous to Ov33, an aspartyl protease inhibitor) induced both a polyclonal and Ag-specific IgE/IgG4 response that was blocked by neutralizing Abs to IL-4 and to IL-13 or by soluble IL-4 receptors. Recombinant human IFN-gamma and IL-12 also led to a decrease in the production of polyclonal and Ag-specific IgE/IgG4 Abs. In addition, these two recombinant proteins preferentially stimulated the secretion of IL-4, IL-5, and IL-10 (in contrast to IFN-gamma). The data suggest that certain epitopes on filarial Ags preferentially elicit a Th2-type response and provide an in vitro model for dissecting the mechanisms underlying this preferential response.

Animals↗
PubMed1995

Induction of opsonizing antibodies after injection of recombinant Plasmodium falciparum vaccine candidate antigens in preimmune Saimiri sciureus monkeys.

We have previously shown that Plasmodium falciparum recombinant antigens PfEB200, R23, and Pfi72 inhibit opsonization of infected erythrocytes by hyperimmune Saimiri sera, indicating that they contain target epitopes involved in the phagocytosis of infected erythrocytes. We have investigated in this study the immune response of Saimiri monkeys with previous experience of malaria infections (preimmune monkeys) after injection of these recombinant antigens, administered alone or simultaneously. The humoral response to the recombinant antigens was monitored by radioimmunoassay, and the response to P. falciparum blood stages was assayed by immunofluorescence. The relative proportion of protective versus nonprotective immunoglobulin subtypes was investigated by using 3A2/G6 and 3E4/H8 monoclonal antibodies, and the capacity of the antisera to promote in vitro phagocytosis of infected erythrocytes was evaluated. The antigens evoked in most cases a secondary-type antibody response, resulting in important increases in antigen-specific antibody titers and concomitantly in anti-P. falciparum titers. The ratio of 3A2/G6 to 3E4/H8 immunoglobulin subtypes varied with the immunogen used. Opsonizing antibodies were boosted in several animals, the most promising combination being the mixture of PfEB200 and R23 that induced long-lasting production in five of five animals. The detectable opsonizing activity appearing after immunization of the animals was antigen specific, as it was lost after adsorption of the recombinant antigens. The challenge of the animals with blood stage parasites confirmed previous findings showing a correlation between the presence of detectable opsonizing antibodies in serum and protection.

Animals↗
PubMed1994

Manipulating blood T cells and B cells from squirrel monkeys: some technical considerations.

The squirrel monkey Saimiri sciureus is an experimental host for a range of human pathogens, and for the assessment of vaccine candidate antigens and vaccine strategies. This experimental host is thus particularly suitable for the follow-up of humoral responses. To understand some of the mechanisms that underlie the defense against experimental pathogens, there is a need of basic knowledge on cellular immune effectors also. The authors report here their experience in characterizing squirrel monkey blood T and B lymphocytes, and in studying in vitro induced activation and proliferation of T and B cells. Particular emphasis is given to the in vitro differentiation of squirrel monkey B cells into immunoglobulin secreting cells, with respect to Plasmodium falciparum antigens.

Animals↗