Search PubMed⌕ Search

Biomedical subjects

D Mazier

Publications and source records attributed to D Mazier.

At least 73 records · Page 4Linked to original sources
PubMed1991

Antibody responses to a synthetic peptide-based malaria vaccine candidate: influence of sequence variants of the peptide.

A synthetic peptide (Asn-Ala-Asn-Pro)3, representing a protective sequence from the sporozoite stage of Plasmodium falciparum, conjugated to tetanus toxoid has undergone clinical testing. Although some protection was obtained, anti-parasite responses were generally low. In attempting to improve the anti-parasite protein antibody response, we evaluated the efficacy of tetanus toxoid conjugates containing seven sequence variants of the peptide. Most of the conjugates tested in both mice and monkeys elicited anti-peptide antibodies with fine specificity differences, although there was a broad degree of cross-reactivity. In general, each conjugate tested evoked similarly high anti-sporozoite antibody responses in both species and, thus, based on antibody titer no evidence for a superior vaccine candidate was obtained. The biological activity of one antiserum actually increased the penetration of sporozoites into human liver cells. In contrast, antisera against the other conjugates inhibited sporozoite penetration, but to a similar degree. Based on these two criteria, none of the other conjugates would appear to be better vaccine candidates than the original conjugate. The lack of concordance between anti-peptide or anti-sporozoite titers and inhibitory activity in the case of one antiserum indicates that these two measures of antibody cannot always be used for predicting anti-sporozoite activity.

Amino Acid Sequence↗
PubMed1991

Inflammatory status and preerythrocytic stages of malaria: role of the C-reactive protein.

In the acquisition of protection against malaria, the role played by nonspecific factors, some being part of the cascade effect of cytokines, has to be considered. The C-reactive protein, a major acute phase reactant secreted by interleukin-1 stimulated hepatocytes, has an effect on the hepatic development of Plasmodia, both by preventing penetration of the sporozoite into the hepatocyte and by blocking parasite division through an antibody-like effect. This latter effect confirms the potential interest of targeting the uninuclear form of the parasite. Nevertheless, C-reactive Protein alone does not account for all the effects of the inflammatory response, other reactants from both serum and hepatocytes are also involved.

Animals↗
PubMed1991

Characterization of murine monoclonal antibodies against a repetitive synthetic peptide from the circumsporozoite protein of the human malaria parasite, Plasmodium falciparum.

Monoclonal antibodies (mAbs) were raised in mice against the synthetic peptide (NANP)40, consisting of 40 (NANP) repeats of the circumsporozoite (CS) protein of the human malaria parasite, Plasmodium falciparum, and characterized. (i) Five of these mAbs recognized the P. falciparum CS protein in western blot experiments and in immunofluorescence assays using different preparations of sporozoites. The remaining two mAbs (CT3.2 and CT3.3, both IgG1) gave negative results by both techniques. (ii) When the anti-(NANP)40 peptide mAbs were functionally tested in vitro to assess their ability to inhibit the attachment and penetration of the parasites into cultured human liver cells, six of them exhibited inhibitory activities ranging between 66 and 90%. CT3.2 mAbs, also, inhibited sporozoite attachment and penetration, despite the negative results by immunofluorescence and western blot experiments. However, when immunofluorescence was repeated in the presence of calcium, CT3.2 did reveal a positive recognition of P. falciparum sporozoites, suggesting that this mAb could recognize the (NANP) sequence when calcium was bound to the repetitive peptide. (iii) Furthermore, the binding of an anti-(NANP)40 IgM mAb (CT1) to the solid-phase peptide was not inhibited by preincubation of the peptide with a mAb against the P. falciparum CS protein. (iv) Finally, one anti-(NANP)40 IgG1 mAb (CT3.1) was unable to bind to the shorter (NANP)3 peptide, although it recognized the (NANP)40 peptide and the P. falciparum CS protein. The results presented here suggest that heterogeneous antibody populations are produced upon immunization of mice with (NANP)40 synthetic peptide and that epitopes different from those simply related to the linear (NANP) amino acid sequence are likely to be present in long (NANP)n constructs as well as in the repetitive domain of the P. falciparum CS protein.

Amino Acid Sequence↗
PubMed1991

TNF inhibits malaria hepatic stages in vitro via synthesis of IL-6.

We examined the capacity of murine recombinant tumor necrosis factor (rmTNF) to induce an inhibitory effect at the hepatic stage on malaria induced by Plasmodium yoelii sporozoites. When injected three times, 1.0 micrograms of rmTNF was found to protect 78% of mice against a sporozoite challenge. In contrast, whatever the dose and the schedule of administration, no inhibition was observed when purified hepatocyte cultures were infected with P. yoelii. The addition of non-parenchymal hepatic cells to hepatocyte cultures restored the capacity of TNF to modulate hepatic stage development, leading to up to 44% inhibition. Antibodies to interleukin 6 reversed the anti-parasite activity in the co-culture system.

Animals↗
PubMed1991

Inhibitory activity of IL-6 on malaria hepatic stages.

Addition of recombinant interleukin-6 (IL-6) to Plasmodium yoelii hepatic cultures resulted in a specific dose-dependent inhibition of parasite development. Time course experiments showed that, without any direct effect on free sporozoites, IL-6 exerts its action during both the early phase of infection and during the subsequent maturation of the schizonts. Elicitation of the oxidative burst appears to be one mechanism by which IL-6 interferes with the development of hepatic phase. Catalase and superoxide dismutase, two scavengers of hydrogen peroxide and superoxide anions, reversed the IL-6 mediated parasiticidal activity.

Animals↗
PubMed1990

Immune responses to defined epitopes of the circumsporozoite protein of the murine malaria parasite, Plasmodium yoelii.

We have investigated the immunogenicity of defined sequences of the circumsporozoite (CS) protein of the murine malaria parasite, Plasmodium yoelii. A 21-ner synthetic peptide from the nonrepetitive region of the CS protein (position 59-79, referred to as Py1) induced T cell proliferative responses in H-2d and, to a lesser extent, in H-2b mice. Conversely, a synthetic peptide (referred to as Py4) consisting of four (QGPGAP) repeats of the P. yoelii CS protein, induced an antibody response only in H-2b mice. No antibody response was observed when the Py3 peptide, consisting of three (QGPGAP) repeats, was used as an immunogen. When cross-linked to the Py4 repetitive peptide, the Py1 sequence behaved as a T helper epitope allowing the production of anti-Py4 antibodies in H-2d mice. Several long-term T cell lines and clones specific for the nonrepetitive Py1 peptide were originated in vitro from both H-2d and H-2b mice. These lines and clones were CD4+ and proliferated in a major histocompatibility complex-restricted fashion. Furthermore, Py1-specific T cell lines and clones did not proliferate in the presence of synthetic peptides from an analogous region of another rodent malaria parasite, P. berghei, despite the high degree of homology existing in this sequence of the two CS proteins. Finally, supernatants from 7 out of 13 clones (from BALB/c mice) produced detectable amounts of interleukin 2 and interferon-gamma; whereas supernatants from the 4 clones from C57BL/6 and 2 from BALB/c mice contained detectable amounts of interleukin 5. These results show that functionally heterogenous CD4+ T cell populations, belonging to either TH1 or TH2 subset, are activated upon immunization of mice with the P. yoelii Py1 synthetic peptide. It is not yet known what differential role these CD4+ subsets play during the malaria infection or after immunization with different malaria T cell epitopes. This knowledge may have a particular impact in the design of effective subunit vaccines against malaria.

Amino Acid Sequence↗
PubMed1990

Peptide-primed CD4+ cells and malaria sporozoites.

We have mapped a T cell epitope in the circumsporozoite (CS) protein of the murine malaria parasite, Plasmodium yoelii. A 21-mer synthetic peptide corresponding to the amino acid positions 59-79 (referred to as Py1), induced specific proliferation in BALB/c and C57BL/6 mice, and provided help for the production of antibodies to peptides from the repetitive region, (QGPGAP)n, of the same CS protein, when mice were immunized with the Py1 peptide conjugated to the repetitive peptide. Long-term CD3+CD4+CD8-TCR alpha beta+ T cell lines and clones were derived from both strains of mice. These lines and clones, that proliferated in an MHC-restricted fashion, did not recognize peptides from the homologous region of another murine malaria parasite, P. berghei. About 50% of these clones produced detectable amounts of IFN-gamma and IL-2, whereas the remaining produced IL-4, IL-5, and IL-6. In preliminary experiments, some of these clones specifically inhibited P. yoelii sporozoite development in vitro and conferred protection in vivo in passive transfer experiments. These findings show that heterogenous T cell populations are activated in mice upon immunization with a short peptide from the P. yoelii CS protein and that some of these cells could be active in the effector arm of the immune response against malaria sporozoites.

Amino Acid Sequence↗
PubMed1990

Hepatic phase of malaria is the target of cellular mechanisms induced by the previous and the subsequent stages. A crucial role for liver nonparenchymal cells.

Both the sporozoites and the erythrocytic stages can modulate the hepatic phase by cytokines, notably IFN-gamma, TNF and IL-6, either directly or as a result of a cascade of events, and by MHC-restricted and antibody-dependent cell-mediated cytotoxicity. The role played by CD8+ T cells in inducing protective immunity against pre-erythrocytic stages is clearly established. The potential interest of triggering peptide-primed CD4+ T cells has to be considered regarding protection. Indeed, CD4+ T cells induced by the non-repetitive part of the CS protein of Plasmodium yoelii are protective, by eliminating malaria from hepatocytes. The crucial role of the liver NPC has to be emphasized, their participation in TNF schizonticidal effect and in ADCC mechanisms being strongly supported by our data.

Animals↗
PubMed1990

Use of a tuberculin purified protein derivative--Asn-Ala-Asn-Pro conjugate in bacillus Calmette-Guérin primed mice overcomes H-2 restriction of the antibody response and avoids the need for adjuvants.

Because of its immunodominancy, and because it is conserved in different geographical isolates of Plasmodium falciparum, the repetitive sequence of the circumsporozoite protein, (Asn-Ala-Asn-Pro)n [(NANP)n], has been envisaged for the development of an anti-falciparum malaria subunit vaccine. However, the murine immune response to (NANP)n peptides, either carrier-free or coupled to carrier proteins, was shown to be inducible only by using strong (e.g., Freund's) adjuvants. Furthermore, response to the carrier-free peptide, administered in adjuvant, is genetically restricted to I-Ab mice. In the present paper, we report that high titers of antibodies against the NANP repetitive epitope were obtained in responder C57BL/6 (H-2b) mice when they were primed with live BCG (bacillus Calmette-Guérin Mycobacterium tuberculosis var. bovis) and immunized once with the synthetic peptide (NANP)40 coupled to tuberculin purified protein derivative (PPD) without the use of any adjuvant. This approach also led to the production of high titers of anti-NANP antibodies in ASW (H-2s), B10.RIII (H-2r), BALB/c (H-2d), C3H/He (H-2k), and DBA/1 (H-2q) nonresponder mice after two injections of the conjugate. In both cases, BCG priming was obligatory for the induction of antibodies reacting with the synthetic peptide. The levels of anti-NANP antibodies in nonresponder BALB/c mice were demonstrated to be comparable to the levels induced after PPD-(NANP)40 immunization in Freund's complete or incomplete adjuvant. The antibodies induced were also capable of recognizing P. falciparum sporozoites in immunofluorescence assays and, furthermore, these antibodies inhibited the penetration of live sporozoites into human hepatocytes in vitro. This system functioned independently of the subjects' resistance or susceptibility to BCG infection. Given the widespread natural exposure to mycobacterial antigens and the extensive use of BCG and PPD in the human population, this approach might be envisaged for vaccination with malaria peptides.

Adjuvants, Immunologic↗
PubMed1990

Hepatic phase of malaria: a crucial role as "go-between" with other stages.

Besides potential interest in itself, the hepatic stage of malaria might play a crucial role as "go-between" with other stages. When present in the parasitophorous vacuole, antibodies induced by both sporozoite and erythrocytic stages efficiently disturb hepatic development of the parasite. Likewise previous and ensuing erythrocytic stages can modulate the "shielded" phase by cytokines, directly or as a result of a cascade of events, and by MHC-restricted or antibody-dependent cytotoxic mechanisms.

Animals↗
PubMed1989

Dual action of anti-sporozoite antibodies in vitro.

With the use of a double staining technique that permits localization of the sporozoite during the process of entering a host cell, we studied the biologic effects of three mAb directed against determinants contained in the circumsporozoite of Plasmodium yoelii. These mAb, which included one IgM and two IgG3, were studied in primary cultures of rodent hepatocytes inoculated with sporozoites of P. yoelii. These results confirm previous reports of the extended action of antibodies on Plasmodium falciparum after entering hepatocytes by producing a strong intrahepatocyte inhibitory effect in addition to the inhibitory effect on sporozoite entry. As with P. falciparum the intracellular effects on P. yoelii liver stages are only observed when the antibodies are present at the time the sporozoite enters the cell. While carrying out experiments on this phenomenon, it was discovered that, at lowered antibody concentrations, an increase in number of maturing liver schizonts occurs, with the increase or enhancement of infection reaching up to 150% of that of controls. It was also observed that there was an inverse relationship between the antibody concentration that was inhibitory and that which enhanced parasite infectivity.

Animals↗
PubMed1989

Primary and secondary responses to (NANP) peptides by Plasmodium falciparum sporozoites in various strains of mice.

The repetitive epitope (Asn-Ala-Asn-Pro = NANP) of the Plasmodium falciparum circumsporozoite protein is considered as the basis for the development of a recombinant or synthetic subunit vaccine against malaria. Vaccines consisting of (NANP)n molecules coupled to carrier proteins have already been tested in trials in human volunteers with partial success. In this paper we show that C57BL/6 mice, genetically responsive to carrier-free (NANP)n molecules, exhibit a secondary antibody response to (NANP) if they are primed with carrier-free (NANP)40 synthetic peptide, and then challenged with P. falciparum sporozoites. However, such a sporozoite-mediated boosting effect is not observed if C57BL/6 and BALB/c mice were previously primed with (NANP)40 peptide conjugated to carrier proteins. The genetic restriction of the murine antibody response to (NANP)n is overcome when mice bearing seven different H-2 haplotypes are immunized with entire P. falciparum sporozoites. These results may have implications for the understanding of natural or induced anti-sporozoite immunity, and show that the use of T-cell epitopes from the plasmodial antigenic repertoire would be very likely to represent an efficient approach for the development of a subunit malaria vaccine.

Animals↗
PubMed1989

C-reactive protein protects against preerythrocytic stages of malaria.

We previously reported that low doses of interleukin-1 strongly inhibited in vitro development of the hepatic stages of Plasmodium falciparum and P. yoelii. Among several hypotheses, we considered the role of C-reactive protein (CRP), a major acute-phase reactant whose concentration increases markedly in infectious disorders. We demonstrated that human hepatocytes cultured in the presence of interleukin-1 released, as early as 30 min after stimulation, an increased amount of CRP. We then established that CRP bound to the P. falciparum and P. yoelii sporozoite surface membranes, probably via a phosphorylcholine binding site. Experiments in which CRP was added to rat hepatocyte monolayers during or after inoculation confirmed that the target of the CRP-mediated inhibition was at the very early phase of infection. These in vitro functional activities were confirmed in an in vivo model; rats with increased levels of CRP in serum following an injection of turpentine oil were found to be largely protected against an inoculation of P. yoelii sporozoites. The same results were observed in animals inoculated with sporozoites previously incubated in purified CRP or in sera of rats pretreated with turpentine oil. The latter effect was inhibited after incubation of serum from turpentine-injected rats with anti-CRP serum.

Animals↗
PubMed1989

Effect of irradiation on Plasmodium sporozoites depends on the species of hepatocyte infected.

The use of models such as rodents immunized with irradiated rodent malaria sporozoites can be helpful in defining the hepatic antigens which elicit a protective response. After "normal" penetration into the hepatocyte, and "normal" transformation, into trophozoites, irradiated sporozoites are known to begin development, but abort after a period of time that depends on the dose of radiation received. Experiments performed with cultured rat, mouse and Thamnomys gazellae hepatocytes infected with Plasmodium yoelii sporozoites demonstrated that the amount of radiation necessary to totally block the passage from the uninuclear to the multinuclear form differs for each species of hepatocyte. These results underline the problem posed by the models used in malaria research.

Animals↗
PubMed1988

Malaria sporozoite penetration. A new approach by double staining.

To determine, whether a sporozoite is outside the hepatocyte membrane or internalized, a double staining test was carried out using, successively, antibody labeled with peroxidase and fluorescein. This test permits the quantification of sporozoite entry and outline sporozoite-hepatocyte interactions.

Animals↗
PubMed1988

Construction of immunogens for synthetic malaria vaccines.

The immunogenicity of a peptide consisting of eight repeats of the tetrapeptide sequence NANP (Asn-Ala-Asn-Pro) contained in the circumsporozoite protein of Plasmodium falciparum was investigated in mice under different modes of presentation. This peptide was able to produce biologically active antibodies when administered with adjuvant and linked to a protein carrier. However, a (NANP) peptide polymerized by carbodiimide was found to be immunogenic in the absence of protein carrier in H-2b mice. In contrast, the (NANP)8 peptide polymerized by glutaraldehyde was not immunogenic in the same strain. Furthermore, the efficacy of murabutide in saline, as an immunological adjuvant, was compared to the efficacy of Freund's complete adjuvant.

Amino Acid Sequence↗