Search PubMed⌕ Search

Biomedical subjects

A Tartar

Publications and source records attributed to A Tartar.

At least 55 records · Page 3Linked to original sources
PubMed1994

Merozoite surface protein-3: a malaria protein inducing antibodies that promote Plasmodium falciparum killing by cooperation with blood monocytes.

We have previously found that the acquired protection against malaria implicates a mechanism of defense that relies on the cooperation between cytophilic antibodies and monocytes. Accordingly, an assay of antibody-dependent cellular inhibition (ADCI) of parasite growth was used as a means of selecting for molecules capable of inducing protective immunity to malaria. This allowed us to identify in the sera of clinically protected subjects an antibody specificity that promotes parasite killing mediated by monocytes. This antibody is directed to a novel merozoite surface protein (MSP-3) of a molecular mass of 48 kD. Purified IgG from protected subjects are effective in ADCI and those directed against MSP-3 are predominantly cytophilic. In contrast, in nonprotected individuals, whose antibodies are not effective in ADCI, anti-MSP-3 antibodies are mostly noncytophilic. A region in MSP-3 targetted by antibodies effective in the ADCI assay was identified and its sequence was determined; it contains an epitope not defined by a repetitive structure and does not appear to be polymorphic. Antibodies raised in mice against a peptide containing this epitope, as well as human antibodies immunopurified on this peptide, elicit a strong inhibition of Plasmodium falciparum growth in ADCI assay, whereas control antibodies, directed to peptides from other molecules, do not. The correlation between isotypes of antibodies produced against the 48-kD epitopes, clinical protection, and the ability of specific anti-MSP-3 antibodies to block the parasite schizogony in the ADCI assay suggests that this molecule is involved in eliciting protective mechanisms.

Amino Acid Sequence↗
PubMed1994

Reduction of a trisulfide derivative of glutathione by glutathione reductase.

Glutathione trisulfide was synthesized from glutathione disulfide and its reduction by glutathione reductase was studied. A two-step reaction was observed. In a first step, the rate of reduction was similar to that observed with glutathione disulfide. In addition to glutathione, a persulfide intermediate was detected by an electrochemical method and was carboxymethylated by iodoacetate to be identified by Plasma Desorption Mass Spectrometry. During the second step the reduction of this intermediate led to the formation of hydrogen sulfide and a second equivalent of glutathione.

Animals↗
PubMed1994

NMR and circular dichroic studies of the solution structure of conformationally constrained antigenic peptides.

Circular dichroic and nuclear magnetic resonance spectroscopies were used to evaluate the conformational properties in solution of a series of 20-amino-acid peptides derived from the primary structure of an antigen from Echinococcus granulosus. The linear peptide corresponding to the sequence 93-112 in the antigen was found to populate in a significant proportion the alpha-helix conformational state. In the presence of 2,2,2-trifluoroethanol, a cosolvent known to stabilize peptide secondary structure, the helical population, estimated from circular dichroic spectra, increases up to 60-70%. Two-dimensional nuclear magnetic resonance studies under these conditions showed that the segment K96-K108 meets all the criteria of an alpha-helix at 281 K and 298 K. Three different variants were synthesized with the same or similar primary structure but containing a lactam-bridged (>) side chain: D107 > K110, D97 > K100 and K94 > E98. Generally, the observed helical content in these variants was lower than in the parent molecule and the stability of the helical conformation decreased in the order D107, K110, K94, E98, D97, K100. Analysis of chemical shift and nuclear Overhauser enhancement data suggested that the lactam rings induce significant distortions of the local features of helix secondary structure. The possible factors of helix destabilization induced by lactam bridges, observed in the studied peptides are discussed in relation to the stabilizing effect of ion pairs in model compounds.

Amino Acid Sequence↗
PubMed1994

Simian immunodeficiency virus as a model for vaccination against HIV. Induction in rhesus macaques of GAG- or NEF-specific cytotoxic T lymphocytes by lipopeptides.

The protection against infection by HIV probably requires the induction of both neutralizing Abs and CTL responses. Vaccination by attenuated HIV is hardly acceptable and the use of viral genes inserted in recombinant living vectors needs further development, especially with respect to safety. The peptidic vaccination is a promising approach but free peptides are usually poorly immunogenic. Because potent immune responses have been obtained in mice with modified peptides such as lipopeptides, we have designed a study to assess the immunogenicity of lipopeptides in nonhuman primates. Seven lipopeptides were synthesized, derived from known immunogenic regions of the simian immunodeficiency virus (SIV) NEF and GAG proteins. Twelve rhesus macaques, randomly chosen and not selected on their MHC basis, were immunized subcutaneously with the seven lipopeptides in IFA. An MHC class I-restricted and CD(8+)-mediated CTL response has been observed in seven macaques directed against one or two of the synthetic immunizing peptides in each case. These CTLs were able to lyse autologous target cells infected with a recombinant vaccinia virus expressing the SIV nef or gag genes, suggesting that they recognized the naturally processed peptides. These activities are detectable in peripheral blood cells for at least 10 mo after the last immunization. Abs against the immunizing peptides have also been observed in all cases. This study demonstrates that lipopeptides can generate cytotoxic and humoral immune responses in a large number of unselected animals and this approach may thus be worth considering in the vaccination against HIV.

AIDS Vaccines↗
PubMed1994

The mixotope: a combinatorial peptide library as a T cell and B cell immunogen.

We report a new approach in peptide vaccine strategy based on combinatorial synthesis. A library of 7.5 x 10(5) related peptides, termed mixotope, was derived from the sequence of the third hypervariable domain (V3 loop) of the human immunodeficiency virus (HIV) envelope protein. This preparation induced a strong immune response in all syngeneic and outbred rodents tested. The response directed against the mixotope included antibodies, CD4+ T helper cells (TH1 and TH2) and CD8+ T cells. In rodents immunized with the mixotope, the T cell response directed against individual V3 peptide sequences (BRU, MN, RF, SF2, and ELI) as measured by T cell proliferation and interleukin (IL)-2 production, was found to be major histocompatibility complex haplotype-dependent. However, additional experiments performed in mice indicated that selectivity was less restrictive when using IL-3 secretion to explore T cell activation. This combinatorial antigen could be considered as a series of agretopic motifs framing a multiplicity of closely related epitopes for T cell recognition and able to elicit a T cell and B cell repertoire. This new construct may therefore provide a basis for the design of future vaccine strategies.

AIDS Vaccines↗
PubMed1994

Effect of a lipopeptidic formulation on macrophage activation and peptide presentation to T cells.

We studied a 45-69 lipopeptide obtained by N-terminal modification with a N epsilon-palmitoyl lysine residue of the 45-69 peptide derived from the nef protein of HIV. T cells from animals immunized intraperitoneally with 45-69 lipopeptide proliferated in vitro in the presence of 45-69 peptide while no response was obtained after intraperitoneal immunization with 45-69 peptide. The efficiency of the 45-69 lipopeptide is supported by the covalent association to the N epsilon-palmitoyl lysine moiety. The immunogenicity of the 45-69 lipopeptide or of the unmodified peptide is dependent on the route of immunization but is not related to a mitogenic effect on cells or to an increase of the peptide antigenicity. Moreover, only 45-69 lipopeptide induces the secretion of cytokines such as IL-1, IL-6 and TNF-alpha by peritoneal macrophages. Finally, the use of 45-69 lipopeptide permits the activation of highly purified T cells without the addition of antigen-presenting cells. These results have implications for the formulation of synthetic vaccines.

Amino Acid Sequence↗
PubMed1994

A novel merozoite surface antigen of Plasmodium falciparum (MSP-3) identified by cellular-antibody cooperative mechanism antigenicity and biological activity of antibodies.

We report the identification of a 48kDa antigen targeted by antibodies which inhibit Plasmodium falciparum in vitro growth by cooperation with blood monocytes in an ADCI assay correlated to the naturally acquired protection. This protein is located on the surface of the merozoite stage of P. falciparum, and is detectable in all isolates tested. Epidemiological studies demonstrated that peptides derived from the amino acid sequence of MSP-3 contain potent B and T-cell epitopes recognized by a majority of individuals living in endemic areas. Moreover human antibodies either purified on the recombinant protein, or on the synthetic peptide MSP-3b, as well as antibodies raised in mice, were all found to promote parasite killing mediated by monocytes.

Amino Acid Sequence↗
PubMed1994

Two-site enzyme immunoassay of cholesteryl ester transfer protein with monoclonal and oligoclonal antibodies.

We developed a sandwich-type enzyme immunoassay to measure cholesteryl ester transfer protein (CETP) mass in human plasma. A specific monoclonal antibody (TP-4) that recognizes an epitope located in the C-terminal domain was used for antigen capture and an anti-CETP peptide antibody directed against the 290-306 residue was used for detection. Bound antibodies were revealed with an antibody-peroxidase conjugate specific for rabbit IgG. The presence of 10 mL/L Triton X-100 in the incubation buffer increased antigen exposure of CETP in plasma. The curves for CETP in standard plasma and partially purified CETP were parallel. This technique is rapid (results within 6 h), accurate, precise (mean intra- and interassay CVs 3.6% and 8.4%, respectively), and simple to perform. Assay sensitivity is at microgram concentrations, with a working range of 20-200 micrograms/L. In 40 normolipidemic healthy subjects, the mean CETP concentration in plasma was 1.1 +/- 0.4 mg/L. A strong correlation between CETP concentration and CETP activity (r = 0.91, n = 42) was observed. In plasma, the bulk of CETP was found in high-density lipoprotein fractions. Therefore, this assay may be a useful tool for investigations of CETP and its significance in relevant diseases.

Antibodies↗
PubMed1994

Preparation of anti-HIV-low-density lipoprotein complexes for delivery of anti-HIV drugs via the low-density lipoprotein pathways.

Lipophilic prodrugs of 3'-azido-3'-deoxythymidine (AZT) and of 2',3'-didehydro-3'-deoxythymidine (D4T) have been synthesized. 3 beta-(2'-carboxymethoxy)-cholest-5-ene acid, palmitic acid, linolenic acid, linoleic acid, and cholanic acid have been covalently bound to AZT and D4T. In some experiments the fluorescent molecule NBD was simultaneously linked. These prodrugs were incorporated into LDL or acetylated LDL. The best incorporation was obtained with drugs presenting a steroid moiety (cholesterol derivative or cholanic acid) in their structure. The incorporation of prodrugs into LDL was estimated as approximately 200 molecules of prodrug per LDL particle. Cytofluorimetric studies clearly show that the NBD-steroid LDL or NBD-steroid acetylated LDL are bound and then internalized by the B-E receptor (U937) or the scavenger receptor (mouse peritoneal macrophage), respectively. The antiretroviral activity of palmitate-D4T, cholanic-AZT, and cholanic-AZT-LDL complex was similar to the activity of free D4T and free AZT, respectively. Development of lipid nucleoside-LDL complexes to attach specifically to cells involved in HIV infection might have a direct clinical relevance.

Animals↗
PubMed1993

Fast immunopurification of small amounts of specific antibodies on peptides bound to ELISA plates.

ELISA is widely used as a means to detect antibodies, but the potential of ELISA plates as an immunosorbent for the purification of specific antibodies does not seem to have been evaluated. In this study, ELISA plates coated with peptides representing short sequences of various antigens from Plasmodium falciparum, the etiologic agent of human malaria, have been successfully used as a means to purify small amounts of the corresponding antibodies. ELISA plates, identical to those used for antibody detection, also permitted the evaluation of various elution conditions for each pairing of peptide and serum; we tested four eluting buffers (0.2 M glycine, pH 2.5; 0.2 M lysine, pH 11.5; 3.0 M MgCl2, 0.075 M Hepes, 25% ethylene glycol, pH 7.1-7.2 and 4 M NH4SCN in 0.1 M NaH2PO4, pH 6.0) with four pairs of peptides and sera. The ELISA plates could also be used to estimate the affinity of the eluted antibodies by the technique of Pullen et al. (1986). The eluted antibodies were compared to those obtained by immunopurification on recombinant proteins adsorbed on nitrocellulose filters. In contrast to the latter, they were not contaminated by antibodies directed against the carrier moiety of the recombinant protein. When used in immunofluorescence assays with various stages of the parasite the antibodies immunopurified on peptides bound to ELISA plates were able to react with the native antigens in the parasite.

Animals↗
PubMed1993

Synthesis and anti-HIV evaluation of D4T and D4T 5'-monophosphate prodrugs.

Several 5-monophosphate D4T derivatives and their analogues were synthesized as potential lipophilic prodrugs of D4T. Cholesteryl D4T phosphate diester and bis-5'-D4T phosphate inhibited HIV replication in CEM-Cl13 cells more efficiently than D4T itself as measured by the inhibition of cytopathic effect based on MTT assay or reverse transcriptase activity. The two compounds were devoid of toxicity on CEM-Cl13 cells at doses equal to 50 and 100 microM, respectively, which brought the selectivity index into the same range as AZT.

Antiviral Agents↗
PubMed1993

Schistosoma mansoni 28-kDa glutathione S-transferase and immunity against parasite fecundity and egg viability. Role of the amino- and carboxyl-terminal domains.

We have previously shown that a mAb that inhibits the enzymatic activity of the Schistosoma mansoni 28-kDa glutathione S-transferase (Sm28 GST) also reduces female worm fecundity and egg viability in vivo and in vitro. By peptidic epitope mapping and an activity reconstitution assay, the carboxyl terminus (CT) amino acid residues 190-211 and to a lesser extent the truncated amino terminus (NT) residues 10-43 of the enzyme were identified as mAb recognition sites. Sera from rats immunized with the NT (10-43) and CT (190-211) peptides showed a partial inhibitory effect on Sm28 GST activity in a late phase (6 to 7 wk) but not in an early phase (2 to 4 wk) after immunization. Passive transfer of Sm28 GST-inhibiting anti-N- and C-terminal sera, but not of the noninhibitory sera, protected the infected mice by reducing tissue egg deposition and the ability of eggs to hatch. In active immunization experiments, the CT peptide significantly decreased the worm burden (37 to 40%) in mice as did the rSm28 GST (28 to 52%). In terms of tissue egg deposition and egg-hatching ability, immunization with both the NT and CT peptides reproduced the reduction observed after immunization with rSm28 GST. A constant reduction in egg numbers was noted in the small intestines and the livers of the immunized mice. A clear reduction in the ability of intestinal or hepatic eggs to hatch was observed. The results are discussed in terms of the conformational participation of the NT and CT of Sm28 in the expression of GST activity.

Amino Acid Sequence↗
PubMed1993

Immunogenicity and antigenicity of synthetic peptides derived from the mite allergen Der p I.

As an immunogen must contain both B- and T-cell epitopes, small peptides are usually reported as non-immunogenic unless coupled to a protein carrier. In this study, the immunogenicity of the Der p I synthetic uncoupled peptides (p52-71, p89-104, p117-133 and p176-187) previously reported as B-cell epitopes, was evaluated. Different schedules of immunization were used. Results indicated that by using the Vaitukaikis' method three injections of the same peptide without protein carrier was sufficient to induce an specific anti-peptide IgG antibody response (evaluated by ELISA). Indeed, the 16-20 amino-acid long peptides p52-71, p117-133 and p89-104 were revealed highly immunogenic in rabbits. Furthermore anti-peptide p52-71 and p117-133 antibodies were shown by Western-blotting or by neutralization assay to recognize the Der p I molecule either in denaturated or native form as well as Der f I (major allergen of Dermatophagoides farinae). Finally, taking into account the location of Der p I-derived peptides in the three-dimensional model of Der p I, the antigenicity and immunogenicity of peptides were discussed.

Allergens↗
PubMed1993

Molecular structure of a Toxoplasma gondii dense granule antigen (GRA 5) associated with the parasitophorous vacuole membrane.

The P21 antigen of Toxoplasma gondii, defined by the monoclonal antibody TG17-113, has been described as a dense granule component, secreted in the parasitophorous vacuole during host cell invasion. The present work reports the cloning of the gene encoding the P21 antigen, for which we propose the name GRA 5. A cDNA library was screened with a rat antiserum raised against an HPLC fraction enriched in the P21 antigen. cDNA clones encoding GRA 5 were selected by antibody selection on the recombinant proteins. All these clones were incomplete at the 5' end. The 5' fragment of the longest cDNA clone isolated by this first screening was used as a probe in secondary screenings of cDNA and genomic DNA libraries. A genomic fragment containing the P21 gene and nearly full-length cDNAs have been isolated and sequenced. The gene encoding GRA 5 is 834 bp long and does not contain any intron. The deduced amino acid sequence of an open reading frame encoding 133 amino acids perfectly matched that of 5 peptides microsequenced from the native antigen. A N-terminal hydrophobic region was found to possess the characteristics of a signal peptide of 25 amino acids. A second hydrophobic domain, bordered by two hydrophilic regions strongly suggests a transmembrane region. This molecular structure is supported by ultrastructural studies showing the association of the P21 antigen with the parasitophorous vacuole membrane.

Amino Acid Sequence↗
PubMed1993

Comprehensive delineation of antigenic and immunogenic properties of peptides derived from the nef HIV-1 regulatory protein.

The Human Immunodeficiency Virus (HIV-1) nef regulatory protein, a protein involved in AIDS pathology, was used as a model to investigate and analyze B- and T-cell epitopes. In this paper, we describe the potential structural basis of antigenic and immunogenic reactivity of synthetic peptides derived from the macromolecular antigen. The relationship between B- and T-cell determinants in the context of regulatory mechanisms involved in immune recognition, while integrating recent data concerning MHC presentation. As a result of the recent progress in the field of peptide recognition and presentation, the potential of the peptide approach for constructing successful synthetic vaccines needs to be continuously re-evaluated.

Amino Acid Sequence↗
PubMed1993

Comparative analysis of biological activities of Der p I-derived peptides on Fc epsilon receptor-bearing cells from Dermatophagoides pteronyssinus-sensitive patients.

The ability of four uncoupled synthetic peptides (p52-71, p117-133, p176-187, p188-199) derived from Der p I, a major allergen from the house dust mite Dermatophagoides pteronyssinus (Dpt) to stimulate Fc epsilon R+ cells from Dpt-sensitive patients was comparatively analysed. Each free peptide may specifically stimulate basophils (Fc epsilon RI+ cells) and platelets (Fc epsilon RII+ cells) from patients with significant levels of anti-Der p I IgE antibodies; p52-71 and p117-133 appear the best cell stimulation inducers. Both concentration-dependent biological activities of Der p I-peptide on Fc epsilon R+ cells are enhanced by coupling peptide to a carrier (as human serum albumin). Interestingly each Der p I-sensitive patient tested presents an individual pattern of response to peptide. Thus, from our results it appears that different Der p I sequences could be involved in the immune response to Der p I.

Adolescent↗