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F Zavala

Publications and source records attributed to F Zavala.

At least 73 records · Page 4Linked to original sources
PubMed1990

CD4+ cytolytic T cell clone confers protection against murine malaria.

A CD4+ T cell clone (A1.6) was derived from spleen cells of mice immunized with irradiated sporozoites. This T cell clone recognizes an antigen that is shared by sporozoites and blood forms of Plasmodium berghei and differs from the circumsporozoite protein. Clone A1.6 displays cytotoxic activity, produces IFN-gamma and IL-2 in vitro, and recognizes the plasmodial antigen in the context of the class II I-Ed molecule. Passive transfer of this CD4+ clone into naive mice resulted in a high degree of protection against sporozoite challenge.

Animals↗
PubMed1990

Altered expression of neutrophil peripheral benzodiazepine receptor in X-linked chronic granulomatous disease.

This study was aimed at determining whether the peripheral benzodiazepine receptor (PBZDR), which is abundantly expressed on mononuclear phagocytes, is involved in host defense mechanisms depending on phagocyte membrane-associated NADPH-oxidase complex. Analysis by reversible and covalent binding of PBZDR expression on human neutrophils shows that it is modulated during NADPH-oxidase activation with phorbol 12-myristate 13-acetate. Based on a series of 17 patients with chronic granulomatous disease (CGD), results show that PBZDR expression is dramatically impaired in X-linked CGD, an inherited disorder due to a mutation on the gene coding for cytochrome b558 NADPH-oxidase component, whereas it is unaffected in autosomal recessive CGD where cytochrome b558 is normally expressed, suggesting a link between PBZDR and cytochrome b558 expressions. PBZDR can be assigned by covalent binding to an 18-Kd membrane protein. These results suggest that the neutrophil PBZDR, which can accommodate the widely prescribed anxiolytic drug Valium (diazepam), is involved in host defense against pathogens, a function that could be affected by neuroimmune interactions.

Enzyme Activation↗
PubMed1990

Incorporation of T and B epitopes of the circumsporozoite protein in a chemically defined synthetic vaccine against malaria.

We show here an effective and novel approach to engineer peptide-based vaccines using a chemically defined system, known as multiple peptide antigen systems (MAPs), to protect an inbred mouse strain from infection against rodent malaria. 10 mono- and di-epitope MAP models containing different arrangements and stoichiometry of functional B and/or T helper cell epitopes from the circumsporozoite protein of Plasmodium berghei were used to immunize A/J mice. While these mice did not respond to the mono-epitope MAP bearing only the B or T epitope, very high titers of antibody and protective immunity against sporozoite challenge were elicited by di-epitope MAPs, particularly those with the B and T epitopes in tandem and present in equimolar amounts. These results, obtained in a well-defined rodent malaria model, indicate that MAPs may overcome some of the difficulties in the development of synthetic vaccines, not only for malaria but also for other infectious diseases.

Amino Acid Sequence↗
PubMed1990

VH and VL region structure of antibodies that recognize the (NANP)3 dodecapeptide sequence in the circumsporozoite protein of Plasmodium falciparum.

The sporozoite form of Plasmodium falciparum displays on its surface the circumsporozoite (CS) protein. The central domain of this protein possesses a reiterated tetrapeptide sequence Asn-Ala-Asn-Pro (NANP), and greater than 90% of the sporozoite-specific antibodies obtained from individuals living in malaria endemic areas recognize epitopes within this repeat sequence. Considering the highly repetitive structure of this naturally occurring antigen and its immunodominance, we were interested in analyzing the structural diversity of antibodies that bind to the (NANP)3 sequence. Molecular characterization of immunoglobulin heavy and light chain mRNA was performed for five hybridomas that produce antibodies with binding specificity for the dodecapeptide (NANP)3. These hybridomas were produced in BALB/c mice by inoculation with whole P. falciparum sporozoites. Sequence analysis and Northern blotting showed that for heavy chain, three hybridomas used VH elements that belong to the VHIX family and two to the VHJ558 family. Four different V kappa subgroups were represented among the light chains. Different D and J kappa segments are also utilized, while four heavy chain gene rearrangements involved the JH4 segment. These results indicated that multiple VH-VL gene combinations can code for reactivity to the (NANP)3 sequence, demonstrating that the murine antibody response to this immunodominant region is structurally heterogeneous.

Amino Acid Sequence↗
PubMed1990

Isolation and characterization of protective cytolytic T cells in a rodent malaria model system.

Protective immunity against malaria is induced by immunization with irradiation-attenuated sporozoites. Here we report the isolation of cytolytic T-cell (CTL) clones from BALB/c (H-2d) mice immunized with either Plasmodium berghei or Plasmodium yoelii sporozoites. The epitopes recognized by these CTL can be mimicked by synthetic peptides corresponding to a homologous region in the CS proteins of both rodent malaria species. Both peptides are recognized by the CTL in the context of the same MHC class I molecule, H-2 Kd. In vivo adoptive transfer of the CTL clones into non-immune syngeneic mice protected them from a lethal challenge of infectious sporozoites.

Amino Acid Sequence↗
PubMed1990

Protective anti-sporozoite antibodies induced by a chemically defined synthetic vaccine.

Chemically defined synthetic polymers, known as multiple antigen peptide systems (MAPs) represent an effective and novel approach for engineering peptide-based vaccines. Ten different mono and diepitope MAP models, containing different arrangements and stoichiometry of functional B and/or T helper epitopes from the circumsporozoite protein of Plasmodium berghei were used to immunize mice. High titers of antibody and protective immunity against sporozoite challenge were elicited by MAPs containing T and B epitopes arranged in tandem and in equimolar amounts. These results indicate that MAPs may serve as a basis for developing subunit vaccines to induce high levels of antibodies against sporozoites.

Amino Acid Sequence↗
PubMed1990

In vivo treatment with benzodiazepines inhibits murine phagocyte oxidative metabolism and production of interleukin 1, tumor necrosis factor and interleukin-6.

We reported previously that benzodiazepines, widely prescribed for their anxiolytic properties, bind to specific receptors on macrophages and modulate in vitro their metabolic oxidative responsiveness. This study was designed to investigate the in vivo effects of benzodiazepine molecules on several macrophage functions. Benzodiazepines injected i.p. exerted a long-lasting inhibition on phagocyte oxidative responsiveness, still detectable 48 hr after injection. This action was dose-dependent, optimally effective at 1 mg/kg and observed at the site of injection within peritoneal cells as well as at a distance, within splenocytes. It was restricted to peripheral and mixed-type molecules whereas the central-type compound, clonazepam, was ineffective, in good keeping with the molecular specificity of the receptor present on murine macrophages. The fact that benzodiazepines exerted similar effects in Nude mice highly suggests that their in vivo inhibitory activity was not T cell-dependent. The peripheral benzodiazepine Ro5-4864 injected i.p. inhibited the capacity of macrophages to produce interleukin-1, tumor necrosis factor and interleukin-6. Clonazepam remained ineffective. These results demonstrate an in vivo immunosuppressive property of peripheral and mixed but not central -type benzodiazepines affecting characteristic phagocyte functions involved in host-defense mechanisms as well as in inflammatory response.

Animals↗
PubMed1990

The conformational restriction of synthetic vaccines for malaria.

The effectiveness of synthetic vaccines is dependent upon the chance event that antibodies formed against largely disordered peptides can bind native protein surfaces which are often ordered. To improve on this situation, new methods are being developed for the conformational restriction of synthetic peptides. Cognate peptide sequences often form predictable secondary structures in proteins characterized by distinct hydrogen-bonding patterns. These weak hydrogen bonds have now been replaced with covalent mimics to conformationally restrict selected peptides to the Type 1 reverse turn and alpha helix. Potential uses for this chemistry are discussed in the context of malaria vaccines. The peptide component of a Plasmodium falciparum sporozoite vaccine, acetyl-(ASN-ALA-ASN-PRO)3-NH2 has been conformationally analysed using two-dimensional nuclear magnetic resonance spectroscopy. These studies are consistent with the formation of transiently ordered turnlike structures which provide a guide for the design and synthesis of a conformationally restricted synthetic vaccine. To assess the effects of conformational restriction and chemical modification on the sporozoite vaccine, ASN side-chains were linked around proline with ethylene bridges. Polyclonal antibodies to this shaped peptide show a strong cross-reaction with living sporozoites.

Animals↗
PubMed1989

Multiple antigen peptide. A novel approach to increase detection sensitivity of synthetic peptides in solid-phase immunoassays.

We describe a novel approach to detect antibodies to synthetic peptide antigens in solid-phase radioimmunoassays, using a multiple antigen peptide (MAP) system. The MAPs consist of multiple copies of peptides that are synthesized as single units on a branching lysyl matrix using a solid-phase peptide synthesis method. The efficacy of the MAP approach in solid-phase immunoassays was compared with the conventional approach using a monomeric peptide of the immunodominant epitope of the circumsporozoite proteins of two species of malaria. Two monomeric peptides with 12 and 17 residues were found to bind poorly to plastic surfaces at a concentration up to 30 micrograms/ml, and showed no immunoreactivity to specific polyclonal or monoclonal antibodies, while the corresponding MAP-containing peptides showed excellent binding capacity and immunoreactivity at a concentration of 0.11 microgram/ml. The immunoreactivity of MAP-containing peptides was also superior to that of monomeric peptides conjugated to a protein carrier. The effects of various arrangements of lysyl branching of MAP on antigenicity were also studied, and the optimal number for lysyl branching of MAP was found to be octameric. Thus, the MAP, by enhancing the coating capacity and the avidity of synthetic peptides, provides increased sensitivity and reliability for the use of synthetic peptide to study antigen-antibody interactions on solid surfaces.

Antibodies↗
PubMed1989

Cloned cytotoxic T cells recognize an epitope in the circumsporozoite protein and protect against malaria.

Protective immunity against malaria is induced by vaccination of hosts with irradiation-attenuated sporozoites. This immunity is mediated in part by neutralizing antibodies that are directed mainly against the repeat domain of the circumsporozoite protein. Early experiments showed, however, that B-cell-depleted mice that are immunized with sporozoites can resist challenge, indicating that T-cell effector mechanisms may also have a role in protection. This idea was supported by the recent observation that protective immunity also requires T-cells expressing the CD8 antigen (CD8+ T cells) whose target is probably the developing liver-stage parasites. Moreover, an oral Salmonella vaccine that expresses the circumsporozoite protein is able to protect against murine malaria in the absence of antibodies. Here we report the identification of an epitope contained within amino acids 249-260 of the Plasmodium berghei circumsporozoite protein that is recognized by H-2Kd-restricted cytotoxic T cells. Passive transfer into mice of cytotoxic-T-cell clones that recognize this epitope conferred a high degree of protection against challenge. These results provide the first direct evidence that CD8+ T cells that are specific for a defined epitope can confer protection against a parasitic infection.

Animals↗
PubMed1989

The conformational restriction of synthetic peptides, including a malaria peptide, for use as immunogens.

A new strategy is advanced for the conformational restriction of peptidyl immunogens. Our approach is to replace putative amide-amide hydrogen bonds with covalent hydrogen-bond mimics. Because on average every other amino acid in a protein engages in this bond, the syntheses of diversely shaped peptides can be contemplated. Synthetic methods for introducing a potential hydrogen-bond mimic into a peptide with alpha-helical potential is reported and the structural consequences are discussed. The replacement of the hydrogen bond with a chemical link will modify as well as shape the peptide. To explore the consequences of these changes, a potential synthetic vaccine for malaria, the repeating tetrapeptide Asn-Pro-Asn-Ala, was conformationally restricted. Antibodies to the shaped malarial peptide showed a strong cross reaction with Plasmodium falciparum sporozoites.

Amino Acid Sequence↗
PubMed1989

Estimate of Plasmodium falciparum sporozoite content of Anopheles stephensi used to challenge human volunteers.

Plasmodium falciparum infected Anopheles stephensi, taken from a group of mosquitoes which had been used to challenge recipients of (NANP)3-TT vaccine, were tested for P. falciparum sporozoite content by an immunoradiometric assay. Seventy-six percent were infected with mean and median sporozoite equivalents per mosquito of 220,994 and 217,398, respectively (SD = 54,911). This sporozoite density is greater than that usually found in the field. These data suggest that this challenge for evaluating P. falciparum sporozoite vaccines is a demanding test of immunity.

Animals↗
PubMed1989

Comparative analysis of ELISAs employing repetitive peptides to detect antibodies to Plasmodium falciparum sporozoites.

In the last few years, a number of different recombinant and synthetic peptides consisting of the repetitive sequence of the Plasmodium falciparum circumsporozoite protein (NANP)n have been produced and used to develop immunoassays for the detection of antibodies against P. falciparum sporozoites in human sera. A comparative study of three enzyme-linked immunosorbent assays (ELISAs) that employed different (NANP)n peptides (the synthetic peptides (NANP)3 and (NANP)40 as well as the recombinant peptides R32tet32 and R32LR) was carried out using serum samples from individuals who were living in different malaria-endemic areas. The results obtained for these peptide-based ELISAs were compared with those obtained for an immunofluorescence assay (IFA) that used glutaraldehyde-fixed sporozoites. All the methods tested exhibited 100% specificity on sera from persons not exposed to malaria, good reproducibility (coefficients of variation ranged from 3% to 15% for peptide-based ELISAs), and good sensitivity. Reproducibility and sensitivity were lower for the IFA than for the peptide-based ELISAs, perhaps because of the subjective element in the interpretation of the results which is inherent in the IFA method. ELISAs based on peptides that contain a higher number of (NANP) repeats, i.e., (NANP)40 and R32tet32 or R32LR, gave results which correlated better with each other than with those obtained with the ELISA that employed a shorter (NANP)3 peptide. (NANP)n-based ELISAs are relatively simple and inexpensive methods for the detection of anti-P. falciparum sporozoite antibodies and can readily be used in epidemiological research in the field. These assays could contribute to a better understanding of the natural history of the host-parasite relationship in malaria research.

Animals↗
PubMed1988

Multiple T helper cell epitopes of the circumsporozoite protein of Plasmodium berghei.

The present findings establish the lack of genetic restriction of the humoral immune response to sporozoites of Plasmodium berghei, corraborating earlier observations that mice of different strains can be protected by immunization with irradiated sporozoites. Most, if not all, anti-sporozoite antibodies are directed against the repetitive B cell epitope of the circumsporozoite (CS) protein. However, neither a peptide containing a dimer of this repeat (17.1), nor a peptide polymer containing multiple repeats induced an antibody response in mice of different H-2 and different genetic backgrounds. A yeast-derived recombinant, containing the repeat domain and part of the surrounding amino and carboxy-terminal regions of the P. berghei CS protein, induces very different levels of antibody in mice of diverse H-2 haplotypes. H-2j mice are high responders and the immunized mice are extensively protected against sporozoite challenge. The lymph node cells of the H-2j mice (but not from other strains) proliferated in the presence of peptide N, contained in the amino terminal region of the CS recombinant. Additional H-2-restricted T cell epitopes have been identified in amino and carboxy-terminal regions of the CS protein, and mice of most of the strains recognized multiple T cell epitopes. Two peptides representing T cell epitopes were synthesized in tandem with a peptide representing the B cell epitope, and were assayed for T helper activity in vivo. The antibody response of mice, primed by a single injection of sporozoites, was boosted very effectively by the administration of peptide N + 17.1 or peptide B-4 + 17.1. The B-4 T cell epitope is located in the carboxy-terminal region of the CS protein and is recognized by mice of at least four different H-2 haplotypes. These observations demonstrate that the immune response to the CS protein of P. berghei is not genetically restricted and that it contains several T cell epitopes, some of which can function as helper epitopes. In addition, they show that a synthetic sporozoite vaccine can boost the immune response to sporozoites.

Animals↗
PubMed1988

Prevalence and levels of antibodies to the circumsporozoite protein of Plasmodium falciparum in an endemic area and their relationship to resistance against malaria infection.

A study on malaria transmission, prevalence of infection and anti-sporozoite antibodies was carried out in Burkina Faso (West Africa). The prevalence and the levels of antibodies to (NANP)3 were found to be related to the entomological sporozoite inoculation rates measured at the same time in a defined area. The major inducer of anti-(NANP)3 antibody production under field conditions is sporozoite inoculation by infected mosquitoes. Levels of antibodies to (NANP)3 vary considerably with age and transmission season. High levels of anti-(NANP)3 antibodies raised under field conditions might offer protection against small inocula of sporozoites.

Adolescent↗
PubMed1988

Anti-sporozoite antibodies and immunity to malaria in a rural Gambian population.

A conserved repeated epitope, (NANP)3, of the circumsporozoite protein of Plasmodium falciparum has been identified previously as a putative target for artificially induced immunity to malaria. We examined the role of humoral responses to this epitope in acquired immunity to malaria in a rural African population. Seropositivity to (NANP)3 was slow to develop (9% positive in subjects aged 1-11 years; 88% in those of 30 years and above), and responses in younger subjects were transient. The poor response in younger subjects did not appear to be due to immunosuppression by concomitant blood stage parasitization. The relationship between levels of anti-(NANP)3 antibodies and parasitaemia changed from positive to negative with age. 126 subjects age 1-11 years were followed through an entire transmission season; those who were seropositive at the beginning ended the season with lower parasite rates (20% vs 59%) and experienced fewer episodes of clinical malaria (0.43 vs 0.67). However, the trend towards increasing susceptibility to clinical malaria in subjects entering the transmission season with lower levels of anti-(NANP)3 antibodies was modest, and combined cross-sectional and longitudinal data indicated that the humoral response to (NANP)3 did not play a major role in the development of immunity to clinical malaria in the population we studied.

Age Factors↗
PubMed1988

Ca2+-channel blockers modulate the oxidative burst induced with arachidonic acid in macrophage-like P 388D1 cells. Interaction with peripheral benzodiazepines.

Ca2+-channel blockers are shown to modulate, like peripheral benzodiazepines, the oxidative burst induced by arachidonic acid in the macrophage-like P 388D1 cell line. Nifedipine (1 and 10 nM) enhanced the cellular response to arachidonate; this stimulation by nifedipine was reversed by PK 1195, a specific antagonist for the peripheral benzodiazepine binding site. Verapamil (5 microM), on the other hand, antagonized the stimulation of the oxidative burst by benzodiazepines. The data suggest some possible interaction of Ca2+-channel blockers at the benzodiazepine binding site or at a secondary step in the activation mechanism. None of the molecules modulated the calcium influx triggered by arachidonate. Instead, the oxidative response of P 388D1 cells to arachidonate was inhibited by K+-channel blockers, quinidine and tetraethylammonium bromide.

Animals↗