Search PubMed⌕ Search

Biomedical subjects

D Mazier

Publications and source records attributed to D Mazier.

At least 91 records · Page 5Linked to original sources
PubMed1988

Pre-erythrocytic stages of plasmodia. Role of specific and nonspecific factors.

Protection against pre-erythrocytic stages of malaria is possible as demonstrated by the generation of resistance after immunization with irradiated sporozoites. However, mechanisms involved are more numerous and intricate than previously believed and it progressively appears that the role of the presumed target, the sporozoite, might be negligible compared with that of the hepatic stage. The comparative use of in vivo and in vitro models clearly demonstrates that the intrahepatocytic parasite can be the target of antibodies, cytokines, phagocytic and cytotoxic cells, nonspecific factors--mechanisms in part induced by the previous or subsequent developmental stages.

Animals↗
PubMed1988

Iron chelators: in vitro inhibitory effect on the liver stage of rodent and human malaria.

The activity of desferrioxamine (Desferal) and desferrithiocin (a newly developed oral iron chelator) was evaluated against the liver stage of Plasmodium yoelii and P. falciparum in the rodent and the human hepatocyte in vitro culture system. The two iron chelators were found to inhibit the liver schizogony of both the rodent and the human Plasmodium species at concentrations achievable in vivo. P. falciparum proved to be more sensitive (ic 95% below 20 micromol/l than P. yoelii (ic 95% 50-100 micromol/l). As assessed by electron microscopy, drug administration was associated with focal clarification of the cytoplasm thought to be reversible. As desferrioxamine and desferrithiocin are known to be equally active on the blood stage of rodent and human plasmodia, iron chelators are deserving of further investigation as potential alternative candidates to existing drugs for radical cure of malaria.

Animals↗
PubMed1988

Immunogenicity of a non-repetitive sequence of Plasmodium falciparum circumsporozoite protein in man and mice.

In the present work, the hypothesis that individuals naturally exposed to Plasmodium falciparum malaria infection in endemic areas produce antibodies directed against non-repetitive epitopes of the circumsporozoite protein was investigated. Using a synthetic peptide reproducing the non-repetitive group-conserved region I sequence, we have shown that specific anti-region I antibodies are detectable in sera from endemic countries. Of these sera, 87% also had antibodies against the immunodominant repetitive epitope (Asn-Ala-Asn-Pro, NANP) of P. falciparum. In order to study the immunogenicity of this non-repetitive epitope, a synthetic peptide consisting of both region I and three (NANP) repeats [RI-(NANP)3] was used to immunize inbred strains of mice. H-2b mice produced antibodies against both the repetitive and the non-repetitive epitope. These antibodies were specific for each epitope, recognized P. falciparum sporozoites in immunofluorescence, and inhibited sporozoite penetration into human liver cells in vitro. Non-H-2b mice were completely unresponsive. Lymph node cells from H-2b mice immunized with RI-(NANP)3 peptide proliferated in the presence of RI-(NANP)3 and of (NANP)4 peptide, but never in the presence of RI peptide alone. These findings demonstrate that in the configuration used (i) the non-repetitive epitope region I does not carry T-helper epitopes; (ii) the (NANP) repetitive epitope may act as a carrier for the immune response to region I in mice; and (iii) therefore, immune response to region I in man probably depends on the recognition of T-cell epitopes similar to those involved in the anti-NANP response: i.e. such a T epitope may be NANP itself in responding individuals or another, not yet recognized, sporozoite T-cell epitope.

Amino Acid Sequence↗
PubMed1987

Plasmodium ovale: in vitro development of hepatic stages.

Primary cultures of human hepatocytes, a culture-derived clone from the human hepatoma Hep G2 line, and cultured rat hepatocytes were inoculated in vitro with Plasmodium ovale sporozoites extracted from Anopheles stephensi, An. gambiae, and An. dirus mosquitoes. Penetration and differentiation of P. ovale sporozoites into trophozoite stage parasites occurred in all three cell types, but with a lower transformation rate in the Hep G2 cell line than in the primary cultured hepatocytes. Further maturation was obtained only in the human hepatocytes, in which the parasites were uninucleate until the third day after infection, before development to 60 micron in length by the eighth day. Additionally, this culture system was used to assess the ability of an anti-P. ovale sporozoite monoclonal antibody to inhibit penetration of sporozoites into hepatocytes and to detect sporozoite determinants in the maturing liver stage parasites.

Animals↗
PubMed1987

Fractionation of mouse malarious blood according to parasite developmental stage, using a Percoll-sorbitol gradient.

Asexual intraerythrocytic malarial parasites permeabilize the membrane of their host cell to small monelectrolytes and anions. Since permeabilization increases with parasite maturation, this property has been used previously to fractionate blood infected with Plasmodium falciparum and P. knowlesi according to the developmental stage of the parasite, using Percoll-sorbitol density gradients. We have extended this method to fractionate mouse blood infected with four species of rodent malaria: P. chahaudi, P. vinckei, P. voelii and P. berghei. While the method works in principle in this case, the polyparasitism which characterizes these species prevented explicit separation according to developmental stage. Hence, erythrocytes harbouring several ring-stage parasites appeared in the same fraction which contained cells hosting a single trophozoite, and polyparasitized trophozoites were associated with singly-infected schizont. This observation implies that permeabilization of the host cell membrane results from the integrated metabolic activity of the parasite(s) and is not related to a specific phase of parasite development.

Animals↗
PubMed1987

Enhanced epitopic response to a synthetic human malarial peptide by preimmunization with tetanus toxoid carrier.

Successful human vaccination by synthetic malarial sporozoite peptides may depend on the choice of an appropriate carrier. Tetanus toxoid (TT) has been proposed because of its safe and widespread use in humans. Paradoxically, however, prior exposure to this toxoid vaccine could produce specific epitopic suppression against synthetic malarial peptides conjugated to this same protein as carrier. Indeed, we have previously reported that such a phenomenon can occur in the case of a synthetic vaccine made with a streptococcal peptide conjugated to TT. Our present study shows that similar results can be observed in mice preimmunized with TT 1 month before the administration of a conjugate containing TT and a Plasmodium knowlesi peptide. Analysis of the isotypic pattern of the antipeptide response showed that the immunoglobulin G1 (IgG1) subclass and especially the IgG2a and IgG2b subclasses were suppressed. In contrast, when a sporozoite peptide from Plasmodium falciparum was coupled to TT, the total antipeptide antibodies and particularly the IgG1 subclass were enhanced by preimmunization by TT. This increase of antipeptide antibodies was correlated with a greater ability of the sera to neutralize sporozoite infectivity. These results indicate that prior exposure to TT does not systematically impair the antibody response against a peptide administered as a peptide-TT conjugate.

Adjuvants, Immunologic↗
PubMed1986

Effect of antibodies to recombinant and synthetic peptides on P. falciparum sporozoites in vitro.

Antibodies were raised in mice immunized with several recombinant and synthetic peptides of the circumsporozoite protein of Plasmodium falciparum. The antibodies were evaluated for protective activity in a human hepatocyte culture system. They exerted their protective effect against the parasite at three points: sporozoite attachment to the hepatocyte surface, entry, and subsequent intracellular development. Inhibition of attachment and entry were found to be related to the antibody titer against the authentic circumsporozoite protein on the sporozoite surface, especially when peptides were administered with alum or complete Freund's adjuvant. Even when invasion was not totally inhibited, the presence of abnormal trophozoites and a frequent inhibition of schizont development in long-term cultures suggested continued activity of antibodies at the intracellular level after sporozoite penetration had been completed.

Animals↗
PubMed1986

[Culture systems for production of promastigote and amastigote forms of Leishmania. Application to serological diagnosis and therapeutic trials].

Several species of leishmania and three methods of cultivation: monophasic, biphasic and co-cultivation were used in a compared study bearing on the intensive production of leishmania. In addition by applying, a new in vivo model, comprising an injection of sarcomatous cells and promastigotes into BALB/c mice and also an extraction on a discontinuous gradient (Radioselectan 60%), it was possible to obtain highly purified isolates of amastigote forms. The use of two antigens: promastigotes and amastigotes, is to be recommended for the serological diagnosis, by indirect immunofluorescence, of kala-azar. The new in vivo model merits further consideration for research concerning new molecules active against leishmania.

Animals↗
PubMed1986

Levels of antibodies to Plasmodium falciparum sporozoite surface antigens reflect malaria transmission rates and are persistent in the absence of reinfection.

Antibodies reacting with Plasmodium falciparum sporozoite surface antigens were measured by an immunofluorescence assay using wet preparations of sporozoites attached to poly-L-lysine-treated glass slides, a procedure which was found to be more specific than one using glutaraldehyde-treated and dried preparations. Subjects recovering from a first attack were found to be negative. In two African villages which differed in the level at which mosquitoes transmit the disease (1 and 100 infective bites per year and per individual), both the prevalence by age group and the levels of anti-sporozoite antibodies differed markedly, as follows. In the low-transmission area, these antibodies were not detected in subjects aged 2 to 10 years; thereafter, prevalence increased gradually with the age of the subject and reached 90% in subjects aged 50 to 80 years. In the high-transmission area, all of the subjects studied, including the younger ones, were positive. Anti-sporozoite antibody levels were independent of the levels of antibodies directed against blood stages. On average, the mean antibody titers were equal to 1/16 in the first village and 1/1,650 in the second one. These results suggest that stage-specific antibodies reflect the cumulative number of sporozoites inoculated in humans by mosquitoes and may therefore have useful epidemiological applications. In addition, the presence of stage-specific antibodies in the sera of African adults collected at different times after departure from the endemic area indicates that they may last for several years. During the course of this study, we observed a heterogeneity of immunofluorescence labeling in parasite populations prepared from mosquito salivary glands. This raises the question of possible qualitative or quantitative antigenic differences or both between one sporozoite and the other.

Adolescent↗
PubMed1985

Complete development of hepatic stages of Plasmodium falciparum in vitro.

An in vitro model was developed to study the hepatic phase of Plasmodium falciparum, the only malaria parasite lethal to man. Primary cultures of human hepatocytes were inoculated with sporozoites of Brazilian and African strains of P. falciparum. On days 1 through 7 after inoculation examination of fluorescence-labeled and Giemsa-stained preparations demonstrated the presence of many intracellular parasites. In three separate sets of experiments all cultures were found to be infected with as many as 650 liver schizonts measuring up to 40 micrometers. After the addition of red blood cells, intraerythrocytic forms of P. falciparum were detected on days 12 and 13 by an immunofluorescence assay, indicating that the hepatic cycle had been completed in vitro.

Animals↗
PubMed1984

Hepatocytes as feeder-layers for in vitro cultivation of Plasmodium falciparum blood-stages.

To improve the in vitro growth of Plasmodium falciparum we attempted to cultivate its erythrocytic stages on monolayers of functionally active hepatocytes. Hepatocytes from Swiss Albino mice were isolated by perfusing the liver with a collagenase solution and were co-cultured with a liver epithelial cell type in RPMI 1640 medium supplemented with 10% human umbilical cord serum. The results show that the presence of hepatocytes improves both the multiplication rates of three strains of P. falciparum already in cultivation and the proliferation of freshly isolated strains. Of nine primary isolates tested, only three could be adapted in the standard conditions, whereas all grew readily in the presence of hepatocytes. After two to three weeks of culture with feeder cells, all the strains could be maintained continuously in standard conditions. Similar results were obtained using hepatocytes from another rodent species. Growth was also improved using the supernatant from hepatocyte cultures. No improvement resulted from the use of two human hepatoma cell lines, one rat hepatoma, human embryonic lung fibroblasts, human liver fibroblasts and rat liver epithelial cells as feeder layers. From these results it appears that better culture media can be designed and that the effect of hepatocytes is probably related to the specific functions exhibited by these cells. Hepatocytes may act either by removing toxic substances, particularly lactic acid in the Krebs and Cori cycles, and/or supplying nutrients essential to the parasite.

Animals↗
PubMed1984

[Obtaining hepatic stages of Plasmodium falciparum in vitro].

Sporozoites of Plasmodium falciparum, obtained by membrane feeding of Anopheles freeborni or A. stephensi with cultured gametocytes, were used to infect monolayers of human hepatocytes. Fluorescent labelling with an African serum as well as Giemsa staining performed from day one to day 7 of cultures, demonstrated the presence of numerous hepatic schizonts measuring up to 40 micron.

Animals↗
PubMed1983

[In vitro infestation of human hepatocytes by sporozoites of Plasmodium vivax: schizogony and liberation of merozoites capable of infesting human erythrocytes].

Human hepatocytes obtained by perfusion of a liver biopsy fragment, were infected in vitro with Plasmodium vivax sporozoites raised in Anopheles stephensi. On day 7 of culture, numerous hepatocytic schizonts ranging in size from 5 to 35 micrometers were observed. The schizont maturation was complete and led to the release of invasive merozoites as shown by in vitro infestation of human red cells layered on the hepatocytes cultures.

Animals↗