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Biomedical subjects

A Saul

Publications and source records attributed to A Saul.

At least 91 records · Page 5Linked to original sources
PubMed1996

The effects of bistratene A on the development of Plasmodium falciparum in culture.

The effects of the marine ascidian compound bistratene A on in vitro cultures of Plasmodium falciparum were assessed. Concentrations from 0 to 1.5 micrograms ml(-1) of the compound were tested. The parasitaemia in asynchronous cultures treated with bistratene A increased normally over the first 40 h, then decreased leaving only gametocytes. When synchronized cultures were treated with a constant dose of 50 ng ml(-1), gametocytes developed more rapidly than they did in control cultures. In addition, gametocytes developed in drug-treated cultures of P. falciparum that normally do not produce gametocytes. Bistratene A appears to inhibit merozoite invasion as well as to induce gametocytogenesis.

Acetamides↗
PubMed1996

Transmission dynamics of Plasmodium falciparum.

Recent models of malaria have been developed by Gupta and her co-workers. A frequent assumption used to illustrate these models is that levels of malaria are controlled by lifelong strain-specific immunity. In this article, Allan Saul examines the predictions this model makes about the equilibrium values of parasite prevalence and the dynamics of an epidemic following the introduction of a new strain. He reaches the conclusion that the stability of malaria makes long-term strain-specific immunity highly improbable, thus rendering models requiring lifelong strain-specific immunity unlikely to be of relevance in most epidemiological contexts.

Journal Article↗
PubMed1996

Experimental human Plasmodium falciparum infections: longitudinal analysis of lymphocyte responses with particular reference to gamma delta T cells.

The kinetics of the gamma delta T-cell response was analysed in the context of the overall haematological response in subjects experimentally infected with sporozoites of Plasmodium falciparum. Numbers of gamma delta and alpha beta T cells and NK cells declined markedly during infection to reach minimum values 12-13 days post-infection when the patients were ill. This decline commenced from the beginning of the erythrocytic cycle and well before parasites could be detected microscopically and clinical symptoms developed. Platelet numbers also declined. In vivo activation of gamma delta T cells was evident with sequential up-regulation of the activation markers CD69 and HLA-DR. gamma delta T cell numbers were highest after treatment with the majority being CD4-CD8-, HLA-DR+ and showing reduced CD45RA expression. Contrary to some published observations gamma delta T-cell percentages remained within the normal range. Little evidence of upregulation of activation or memory markers was observed in the alpha beta T-cell population. In vitro proliferative responses to malaria antigen which involve gamma delta T cells were lost as the infection progressed and the lymphocyte count declined but these could be restored with the addition of exogenous IL-2 to cultures. The authors findings are consistent with a protective and/or immunomodulatory role for gamma delta T cells in malaria.

Adult↗
PubMed1996

DNA probes for the Anopheles punctulatus complex.

Genomic DNA probes were made for two recently identified members of the Anopheles punctulatus complex; Anopheles sp. near punctulatus from Papua New Guinea and Anopheles farauti No. 7 from the Solomon Islands. The probes are species-specific and with the use of 32P labeling sensitive enough so that a squash blot of only a small segment of the mosquito is required for identification. The 119-basepair (bp) probe for An. sp. near punctulatus and the 1,106-bp probe for An. farauti No. 7 have been sequenced in full and the probes have been tested on field collected specimens. These probes now make it possible to distinguish An. sp. near punctulatus and An. farauti No. 7 from the other eight members of the An. punctulatus complex. A pan-species probe was also made from the 18S ribosomal DNA that binds to DNA from all members of the complex. These three probes complete the set required for distinguishing all known members of the An. punctulatus complex by DNA hybridization.

Animals↗
PubMed1996

Misidentification of a Philippine malaria vector revealed by allozyme and ribosomal DNA markers.

Morphologically identified Anopheles flavirostris (Diptera: Culicidae), the principal malaria vector in the Philippines, comprised two species in collections from the Bataan Province of Luzon based on allozyme and internal transcribed spacer 2 ribosomal DNA analysis. Seven percent of morphologically identified specimens were the closely related nonvector An. filipinae. Morphologic variability of An. filipinae may account for some of these misidentifications. Genetic identification tools promise to be useful not only for verifying the identification of morphologically defined taxa but also for detecting the presence of morphologically indistinguishable sibling species in the Philippines.

Animals↗
PubMed1995

Computer model of the maintenance and selection of genetic heterogeneity in polygamous helminths.

A stochastic simulation model of the transmission and maintenance of genetic heterogeneity in the absence and presence of external selection pressures is presented for polygamous intestinal helminths such as Ascaris. The model assumes that the density distribution of the adult parasites is highly aggregated and that density-dependent effects on fecundity are important. The model gives rise to stable infection rates in the host. Where the parasite population contains genetic heterogeneity, with the exception of stochastic fluctuations which models genetic drift, the ratio of the different alleles remained constant over extended periods of time. This result contrasts with that of an earlier analytical model (Anderson, R.M., May, M.R. & Gutpa S. (1989) Parasitology 99, S59-S79), in which uneven mating probabilities for the different combinations of worm possible in a host was postulated to inevitably lead to fixation of the most abundant allele. New results suggest that in spite of the restricted choice of mating available to a worm in the confines of a host, selection pressure always leads to enrichment of the parasites carrying resistant alleles.

Animals↗
PubMed1995

Preparative scale purification of recombinant proteins to clinical grade by isotachophoresis.

An electrophoretic procedure based on isotachophoresis has been developed for protein purification on a preparative scale in the 10 to 500 mg range. The system is simple, uses well understood physical properties, does not need ampholyte spacers and is able to produce sterile products of clinical grade. We demonstrate the applicability of this apparatus for the purification of denatured recombinant proteins and complex mixtures of proteins. The system may also be used for both cationic and anionic purification of proteins in their native form. The system is scalable from analytical to preparative protein loads at consistently high protein yields and purity levels. Total protein loads may vary as much as 1000 fold with the use of interchangeable columns of varying diameter and constant length. At both preparative and analytical scales concentration of products at greater than 20 mg/ml are obtainable. Toxicological considerations are addressed with assays for endotoxin, acrylamide and SDS concentrations, as well as the prevention of covalent protein modification.

Electrophoresis↗
PubMed1995

Immunogenicity of recombinant Plasmodium falciparum rhoptry associated proteins 1 and 2.

Mice and rabbits immunized with recombinant forms of malaria vaccine candidate antigens rhoptry-associated proteins 1 and 2 (RAP-1, RAP-2 and rRAP-1, rRAP-2) produce antibodies at titres equivalent to monoclonal antibody ascites fluid raised against the native proteins. Sera from animals immunized with rRAP-1 contain antibodies which recognize the native protein by indirect immunofluorescence and immunoblotting, partially inhibit erythrocyte invasion in vitro and are long lasting. Epitope mapping shows these antibodies predominantly recognize epitopes in the N-terminal third of rRAP-1, some of which coincide with the targets of inhibitory monoclonal antibodies. By contrast, sera from animals immunized with rRAP-2 contain antibodies which recognize the recombinant but not the native protein.

Amino Acid Sequence↗
PubMed1995

Safety, immunogenicity, and pilot efficacy of Plasmodium falciparum sporozoite and asexual blood-stage combination vaccine in Swiss adults.

This study was part of a larger program to develop a vaccine effective against Plasmodium falciparum infection caused by sporozoites and clinical malaria caused by asexual blood stages. In a phase 1 study of safety and immunogenicity, two recombinant proteins (Ro 46-2717, a circumsporozoite [CS] protein) construct with a molecular mass of 35 kD, and Ro 46-2924, a merozoite surface antigen [MSA-2] construct with a molecular mass of 25 kD) adsorbed onto alum were injected in two low (20 micrograms) or two high (100 micrograms) doses in the right and left deltoid muscles of 33 healthy Swiss volunteers; six other volunteers received a placebo (alum alone). Twenty-six participants reported 51 immunization-related adverse events, mainly pain at the injection site. Mean antibody titers to CS protein and MSA-2 in an indirect immunofluorescence assay peaked four weeks after the second immunization without evidence of boosting (i.e., sharp increase in titer). By that time, 56% and 31% of the vaccinees seroconverted to CS protein and MSA-2, respectively, with the increase in MSA-2 titer being weaker than that for the CS protein. After a third immunization, five vaccinees volunteered to be challenged by three or four infective bites of Anopheles stephensi. Prepatent and incubation periods in all five were comparable with unvaccinated historic controls challenged under similar conditions, and all had symptoms of clinical falciparum malaria. We conclude that the vaccine components were safe and immunogenic but there was no evidence that this immunization regimen with the CS protein plus MSA-2 component was able to prevent infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1995

Discrimination of all members of the Anopheles punctulatus complex by polymerase chain reaction--restriction fragment length polymorphism analysis.

A method has been developed to identify the members of the Anopheles punctulatus complex using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Members of the An. punctulatus complex are the most important vectors of malaria in the southwest Pacific and consist of 10 cryptic species, An. farauti no. 1-7, An. punctulatus, An. sp. near punctulatus, and An. koliensis. For each species, PCR amplification of the ribosomal DNA internal transcribed spacer produced a 750-basepair product. Digestion with Msp I and electrophoresis on a 3.0% agarose gel results in banding patterns unique to each species. Isolates of the same species from different locations gave an identical pattern. The technique is sensitive enough so that a PCR-RFLP can be generated from as little as a single mosquito leg, allowing the rest of the mosquito to be used for other important epidemiologic analyses such as determining host feeding source, and for parasite detection.

Animals↗
PubMed1994

Three unrelated Rh D gene polymorphisms identified among blood donors with Rhesus CCee (r'r') phenotypes.

Human red blood cells are traditionally typed as Rhesus (Rh)-positive or -negative depending on the presence or absence of the Rh D antigen. A recent report demonstrated that the Rh D gene is completely absent in Rh D-negative individuals. In this study, Rh D-negative blood donors with ccee (n = 25) and CCee (n = 3) phenotypes were examined for the presence of absence of the D gene. Polymerase chain reaction (PCR) probes that hybridize to the 5' and 3' regions of the Rh CcEe gene and the closely related D gene were used in a Southern analysis. The D gene was absent in all ccee phenotypes examined. The CCee phenotypes showed three Rh D polymorphisms: one donor lacked the D gene, one donor had a partial deletion on one D gene at the 3' region, and the remaining donor appeared to have one normal D gene within the intron/exon regions examined. We conclude that, while the D gene may be absent in the majority of Rh D-negative phenotypes, rarer polymorphisms also occur that prevent expression of the D antigen resulting in the Rh D-negative phenotype.

Base Sequence↗
PubMed1994

A southern analysis of Rh blood group genes: association between restriction fragment length polymorphism patterns and Rh serotypes.

Polymorphisms within the Rh blood group system have been defined by serologic agglutination methods, but have not yet been defined at the DNA level. Two closely related genes associated with the Rh D antigen and with the Rh C/c and E/e antigens have been cloned. We used a Southern analysis incorporating probes to the 5' and 3' regions of the Rh C, E gene and D gene to identify polymorphisms associated with Rh C/c and E/e antigens, respectively. The D gene dosage could be determined by comparing the relative intensities of the D bands with bands from the 5' and 3' region of the Rh C, E gene. The concordance between restriction fragment length polymorphism (RFLP) patterns and serologic phenotypes for 102 randomly selected blood donors was 100% for C, e, and D, 94.8% for c, and 94.3% for E. The data are consistent with the sequences encoding the C/c epitopes residing on the 5' side of those for the E/e epitopes. All samples discordant for the 3' probe and E had the cE (r") serotype. These data show that the gene coding for the cE serotype is different in Rh-positive and -negative individuals. The study demonstrates that Rh DNA typing, including D gene dosage measurements and Rh gene haplotyping, may supplement traditional serotyping methods in transfusion medicine.

Amino Acid Sequence↗
PubMed1994

Sequence variation in the circumsporozoite protein gene of Plasmodium vivax appears to be regionally biased.

We have sequenced the circumsporozoite protein gene from 16 isolates from China, the Philippines, Papua New Guinea and the Solomon Islands. We found very limited polymorphisms in the non-repetitive regions of the circumsporozoite gene from these isolates. All samples from China contained a 36-base insert 3' to the repeats previously seen only in a North Korean isolate. Limited variation was found in the repeat regions, which allowed these and previously sequenced isolates to be classified into groups based on repeat structure. These groupings also correlate with the geographical origin of the isolates.

Amino Acid Sequence↗
PubMed1994

Plasmodium falciparum genetic diversity can be characterised using the polymorphic merozoite surface antigen 2 (MSA-2) gene as a single locus marker.

The genetic diversity of Solomon Island Plasmodium falciparum isolates was examined using MSA-2 as a single locus marker. Amplification of MSA-2 gene fragments showed size polymorphism and the presence of mixed infections. Sequence analysis indicated a global representation of MSA-2 alleles with representatives of 3D7/CAMP allelic subfamilies and the FCQ-27 allelic family being identified. A simplified method of characterisation, utilising PCR-RFLPs of MSA-2 gene fragments, was developed. The RFLPs allowed identification of allelic families and further distinction within the 3D7/CAMP family. The amplification of MSA-2 gene fragments from culture derived lines revealed a loss of diversity for a number of Solomon Island isolates. Genomic diversity was confirmed for Solomon Island lines, along with Papua New Guinean and Thai lines, by the generation of 7H8/6 fingerprints. All lines were distinct and band sharing frequencies and Wagner tree construction failed to identify any geographic clustering.

Amino Acid Sequence↗