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Biomedical subjects

A M Johnson

Publications and source records attributed to A M Johnson.

At least 307 records · Page 17Linked to original sources
PubMed1988

HIV surveillance by testing saliva.

Saliva specimens were tested for HIV antibody (anti-HIV) by an immunoglobulin G (IgG) antibody capture radioimmunoassay (GACRIA) and three sensitive commercial assays. In tests on 460 seronegative subjects and 196 seropositive subjects GACRIA was 99.8% specific and 100% sensitive. The Wellcome HIV monoclonal and Abbott recombinant DNA enzyme-linked immunosorbent assays (ELISAs) were also highly specific (99.8%, 100%) but they were less sensitive (90.9%, 82.0%). The Fujirebio particle agglutination assay was sensitive (97.8%) but its specificity was poor (84.1%). In testing saliva specimens from populations with an anti-HIV prevalence greater than 0.5%, sampling by GACRIA alone could provide a good estimate of the true prevalence. For true prevalences less than 0.5% good estimates could only be obtained if positive GACRIA reactions were confirmed by another independent salivary assay. Salivary testing for anti HIV is a convenient and potentially an accurate epidemiological tool.

Acquired Immunodeficiency Syndrome↗
PubMed1988

Detection of Campylobacter pylori DNA by hybridisation with non-radioactive probes in comparison with a 32P-labelled probe.

A dot-blot hybridisation assay for the detection of Campylobacter pylori was used to compare a 32P-labelled probe with two biotinylated probes and a sulphonated probe. The minimum amount of pure C. pylori DNA that could be detected by the 32P-labelled probe was 100 pg, which corresponded to 5 x 10(4) bacteria. A biotin-labelled DNA (biotin-DNA) probe together with the BluGeneTM detection system produced by Bethesda Research Laboratories (BRL), and a sulphonated probe and ChemiprobeTM detection system (Orgenics) gave similar levels of sensitivity; nylon membranes could be used with both these non-radioactive detection systems. However, a photobiotin-labelled DNA (photobiotin-DNA) probe and detection system produced by Biotechnology Research Enterprises S.A. (BRESA) gave optimum results only with nitrocellulose membranes, and was quantitatively 100 times less sensitive than the other types of probe. The detection systems for the biotin-DNA and photobiotin-DNA probes produced non-specific reactions with crude bacterial blots of heterologous organisms; these non-specific reactions could be removed by treating the dot blots with proteinase K, but not by treatment with RNAase. The sulphonated probe and detection system did not give any reaction with heterologous organism blots.

Azides↗
PubMed1988

Prevalence of Toxoplasma gondii antibody in wild macropods.

An enzyme-linked immunosorbent assay (ELISA) was developed to measure total antibody to Toxoplasma gondii in serum samples from macropods. The validity of the assay was established by comparing parasite isolation in mice for 17 Tasmanian pademelons (Thylogale billardierii) and 17 Bennett's wallabies (Macropus rufogriseus rufogriseus). The ELISA was then used to detect antibody against T. gondii in serum from 236 macropods, collected from 21 locations in Tasmania, including Flinders Island. Antibody against T. gondii was detected in 20 animals (15 T. billardierii and 5 M. rufogriseus). There was a significant (p less than 0.01) difference in possession of T. gondii antibodies between adult (greater than or equal to 1 year of age) Tasmanian pademelons and Bennett's wallabies.

Animals↗
PubMed1988

Phylogenetic relationships of the apicomplexan protist Sarcocystis as determined by small subunit ribosomal RNA comparison.

Reverse transcription of total cellular RNA was used to obtain the partial nucleotide sequence of the small subunit ribosomal RNA (srRNA) of Sarcocystis gigantea. The sequence was compared with the homologous sequences of 24 other eukaryotes. Phylogenetic analysis of the semiconserved regions by 4 different tree-building methods using bacteria as an outgroup all concur in showing monophyly of Sarcocystis gigantea and Toxoplasma gondii to the exclusion of all other taxa for which homologous sequences are available.

Animals↗
PubMed1987

Is it possible to predict the minimum size of the acquired immunodeficiency syndrome (AIDS) epidemic in the United Kingdom?

A mathematical model of the dynamics of transmission of human immunodeficiency virus within the male homosexual population in the United Kingdom demonstrates that even the minimum size of the acquired immunodeficiency syndrome (AIDS) epidemic in the United Kingdom (based upon the assumption that all transmission ceased at the end of 1986) is difficult to predict. Model predictions are particularly sensitive to assumptions about the distributed incubation period of the disease, differences in frequency and patterns of sexual activity, and the proportion of infected people in whom AIDS later develops. More accurate predictions will depend on the collection of data on the incubation period of the disease, the infectiousness of infected persons, and on the numbers of new sexual partners of each sex per person and the duration of each partnership.

Acquired Immunodeficiency Syndrome↗
PubMed1987

Prevalence of antibodies to human immunodeficiency virus, gonorrhoea rates, and changed sexual behaviour in homosexual men in London.

The prevalence of antibody against human immunodeficiency virus (anti-HIV), which rose among British homosexual/bisexual men attending a London sexually-transmitted-disease clinic from 3.7% (4/107) in March, 1982, to 21% (26/124) in July, 1984, was 18.1% (17/94) in April/May 1985, 24.5% (61/249) in January, 1986, and 25.3% (25/99) in November/December, 1986. This slower rise in anti-HIV prevalence coincided with a fall in the annual gonorrhoea rate from 15.3% in 1982 to 5.1% in the first half of 1986 in the same male homosexual clinic population. Over the same period a reduction in the number of sexual partners and a change to safer sexual practices has been documented among homosexual and bisexual men taking part in a prospective study of the natural history of HIV infection. These data support the value of continuing preventive efforts to control viral spread in the absence of an effective vaccine or therapy.

Acquired Immunodeficiency Syndrome↗
PubMed1987

Biochemical effects of the antidepressant paroxetine, a specific 5-hydroxytryptamine uptake inhibitor.

Paroxetine was shown to be a potent (Ki = 1.1 nM) and specific inhibitor of [3H]-5-hydroxytryptamine (5-HT) uptake into rat cortical and hypothalamic synaptosomes in vitro. Lineweaver-Burk kinetic analysis determined that this inhibition was competitive in nature, implying a direct interaction with the 5-HT uptake transporter complex. Oral administration of paroxetine produced a dose-related inhibition of [3H]-5-HT uptake (ED50 = 1.9 mg/kg) into rat hypothalamic synaptosomes ex vivo with little effect on [3H]-l-noradrenaline (NA) uptake (ED50 greater than 30 mg/kg). This selectivity for 5-HT uptake was maintained after oral dosing for 14 days. Paroxetine (ED50 1-3 mg/kg PO) prevented the 5-HT depleting effect of p-chloroamphetamine (PCA) in rat brain, demonstrating 5-HT uptake blockade in vivo. Radioligand binding techniques in rat brain in vitro showed that paroxetine has little affinity for alpha 1, alpha 2 or beta adrenoceptors, dopamine (D2), 5-HT1, 5-HT2 or histamine (H1) receptors at concentrations below 1000 nM. Paroxetine demonstrated weak affinity for muscarinic receptors (Ki = 89 nM) but was at least 15 fold weaker than amitriptyline (Ki = 5.1 nM). Paroxetine, therefore, provides a useful pharmacological tool for investigating 5-HT systems and furthermore should be an antidepressant with reduced tricyclic-like side-effects.

Animals↗
PubMed1987

Toxoplasma gondii and Hammondia hammondi: DNA comparison using cloned rRNA gene probes.

A mung bean nuclease genomic library of purified DNA from tachyzoites of the RH strain of Toxoplasma gondii was prepared in the bacteriophage lambda gtll and recombinants containing rRNA gene fragments were detected by hybridization with radiolabeled total RNA from the closely related coccidian Eimeria acervulina. Ten recombinants were chosen at random, and five of these were investigated further using probes for the genes of the large and small rRNA of Plasmodium berghei. An insert (called TG4) that hybridized only to the 3' end of the large rRNA coding region of P. berghei and an insert (called TG18) that hybridized only to the small rRNA coding region of P. berghei were purified by electrophoresis in low melting point agarose. Radiolabeled E. acervulina total RNA, TG4, and TG18, were then used to compare the sizes of the large and small rRNA gene fragments after DNA extracted from three strains of T. gondii, and the type strain of the closely related coccidian Hammondia hammondi were cut by one of a series of 10 restriction endonucleases. The patterns obtained for the three T. gondii isolates were identical to those obtained for H. hammondi, for each enzyme tested. In addition, the guanine plus cytosine (G + C) content of H. hammondi DNA was found to be almost identical to that obtained previously for T. gondii DNA.

Animals↗
PubMed1987

Rapid nucleotide sequence analysis of the small subunit ribosomal RNA of Toxoplasma gondii: evolutionary implications for the Apicomplexa.

A method for obtaining a large proportion of the nucleotide sequence of the small subunit ribosomal RNA (srRNA) was applied to the obligate intracellular protozoon Toxoplasma gondii. The method uses reverse transcription of as little as 8 micrograms of total cellular RNA. This fast, efficient method has numerous advantages over traditional gene cloning methods when nucleotide sequences are required for evolutionary studies. A phylogenetic analysis of the srRNA sequence data showed that T. gondii is not especially closely related to any other organism for which srRNA sequences are available, including another member of the Apicomplexa.

Animals↗
PubMed1987

Recognition by the human immune system of candidate vaccine epitopes of Toxoplasma gondii measured by a competitive ELISA.

A competitive ELISA for the detection of human antibody to specific candidate vaccine epitopes of Toxoplasma gondii is described. The method is based on competition between antibody in human serum and murine monoclonal antibody to bind to a crude sonicated antigen of T. gondii. A total of 301 normal human sera were tested against a panel of four anti-T. gondii murine monoclonal antibodies. The results obtained with two of the monoclonal antibodies (FMC 22 and FMC 23) gave good agreement with those of an indirect ELISA for human IgG to T. gondii, a measure of previous exposure to the parasite. The epitopes against which these two monoclonal antibodies are directed were recognized by the immune system of all patients previously exposed to the parasite, while greater than 92 and greater than 96% respectively of these patients recognized the epitopes which the other two monoclonal antibodies (FMC 18 and FMC 19) are directed against. An ELISA double antibody binding system was used to ascertain relationships in the epitope binding sites of the four monoclonal antibodies. The data obtained demonstrated that FMC 19 and FMC 22 bound to related epitopes. FMC 18, FMC 22 and FMC 23 also bound to related epitopes, but the binding of FMC 19 was found to be independent of the binding of FMC 18 and FMC 23 to their epitope binding sites.

Animals↗
PubMed1987

Nephelometric immunoassay.

The theory of the scattering of light by particles is summarised and the principles underlying instrumentation for nephelometry in immunoassays are outlined. Consideration is given to the various factors that influence nephelometric assays and methods for increasing sensitivity are discussed.

Journal Article↗
PubMed1987

Mating type linked mutations which disrupt the uniparental transmission of chloroplast genes in chlamydomonas.

In Chlamydomonas reinhardtii, chloroplast genomes are normally transmitted by the mating type plus (mt+) parent and mitochondrial genomes by the mating type minus (mt-) parent. In this paper we describe three new nuclear mutations, designated mat-3-1 to -3, which are tightly linked to the mt+ allele and permit high transmission of chloroplast genomes from the mt- parent, but have no effect on transmission of mitochondrial genomes. We also show that mat-1, reported by others to be a nuclear mutation linked to mt- which promotes transmission of chloroplast genomes by the mt- parent, is probably a vegetative diploid since it contains both mt+ and mt- alleles. Vegetative diploids behave as if they are mt- with respect to mating, but possess a level of chloroplast gene transmission intermediate between that of haploid mt- and mt+ stocks.

Chlamydomonas↗
PubMed1987

Antibody patterns in the serological diagnosis of acute lymphadenopathic toxoplasmosis.

Sera from six patients at various stages of acute lymphadenopathic toxoplasmosis were tested using nine different types of test currently available for the serological diagnosis of the disease. A diagnosis was made on positive serology in three of the patients. The antibody patterns of two of these patients were studied over a period of six months and the third was studied over two months. A diagnosis was made on lymph node morphology in the other three cases. Two serum samples were tested from each of these patients. The results obtained suggest that a rationalisation of the types of test used should be encouraged and that an enzyme-linked immunosorbent assay (ELISA) for parasite-specific IgG and an antibody class capture ELISA for parasite-specific IgM are sufficient to confirm the diagnosis of acute lymphadenopathic toxoplasmosis.

Adolescent↗
PubMed1986

The acquired immune deficiency syndrome and epidemic of infection with human immunodeficiency virus: costs of care and prevention in an inner London district.

The epidemic of the acquired immune deficiency syndrome (AIDS) and infection with human immunodeficiency virus (HIV) necessitates early planning of services and allocation of resources. The use of hospital resources by patients with AIDS and the planned additional costs of clinical and preventive services for the epidemic of infection with HIV were calculated for an inner London health district that has treated 18% of the cases in the United Kingdom. Patients with AIDS required on average 50 days of inpatient hospital care each at an estimated current average lifetime cost of pounds 6800. These costs, however, underestimated the additional capital and revenue costs of planned new preventive and treatment services, estimated as being pounds 388,000 revenue and pounds 472,000 capital for 1986-7. It is important to invest now in preventive services throughout the United Kingdom to reduce the future social and financial costs of AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1986

Characterization and in vitro translation of Toxoplasma gondii ribonucleic acid.

RNA was extracted from purified tachyzoites of Toxoplasma gondii (RH strain) by sequential centrifugation in guanidine hydrochloride, urea, and lithium chloride. The subunits of the RNA were characterized by denaturing and non-denaturing electrophoresis in agarose gels. Poly(A)+-RNA, purified by oligo(dT)-cellulose affinity chromatography, was translated in a rabbit reticulocyte lysate assay and the products were immunoprecipitated with an experimentally infected mouse serum and a naturally infected human serum. After sodium dodecyl sulphate-polyacrylamide gel electrophoresis, fluorography of the polypeptides confirmed that the mRNA translated specific parasite antigens.

Animals↗
PubMed1986

Purification and characterization of Toxoplasma gondii tachyzoite DNA.

Toxoplasma gondii DNA from RH strain tachyzoites was purified from contaminating murine DNA by isopycnic density gradient ultracentrifugation in CsCl containing the fluorescent dye Hoechst 33258. Quantitative hybridization studies with DNA from uninfected mice and DNA extracted from oocysts of the ME49 strain of T. gondii confirmed that RH strain DNA could be obtained at least 90% pure with a high recovery. Preliminary characterization studies on such purified DNA showed that it had a G + C content of 50% and was not significantly methylated.

Animals↗