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Biomedical subjects

M E Ward

Publications and source records attributed to M E Ward.

At least 19 recordsLinked to original sources
PubMed1995

Extent and kinetics of genetic change in the omp1 gene of Chlamydia trachomatis in two villages with endemic trachoma.

Variants of Chlamydia trachomatis in two Gambian villages with hyperendemic trachoma were analyzed by omp1-based polymerase chain reaction and sequencing from conjunctival swabs. Samples collected over a 22-month period included a complete cross-sectional study of each village. Overall, 4 genovar A and 4 B variants were characterized by point mutations in the omp1 gene, resulting in changes in the inferred amino acid sequence. Two genovar A and 2 B variants accounted for 87% of the total ocular chlamydial infection in both villages. Although some flux in the prevalence of individual variants was observed overtime, their overall distribution remained remarkably stable. There was no evidence of major antigenic shift arising from recombination events at the omp1 locus as described for genital tract infection. These results indicate that omp1 variation in these two trachoma-hyperendemic communities is limited and unlikely to hamper development of trachoma vaccines based on the major outer membrane protein.

Amino Acid Sequence↗
PubMed1995

SCOTI--a new device for identification of tracheal intubation.

A new lightweight device for the detection of placement of a tracheal tube in the trachea or oesophagus is described. The device utilises a sonic technique detecting resonating frequencies in an open (trachea) or closed (oesophagus) structure. Evaluation of the device in a clinical environment is described and it has been shown to be capable of verifying the correct placement of the tracheal tube in the trachea in 98% of patients studied. Further evaluation of this intubating aid appears justified.

Adolescent↗
PubMed1995

The immunobiology and immunopathology of chlamydial infections.

Chlamydiae are obligate intracellular bacterial pathogens of eukaryotic cells responsible for a wide variety of important human and animal infections. In humans, chlamydial infections are generally localised to superficial epithelial or mucosal surfaces, are frequently asymptomatic and may persist for long periods of time if untreated, inducing little protective immunity. Nevertheless, neutralising antibodies of limited efficacy are produced against the main chlamydial outer envelope protein, while gamma interferon (IFN gamma) is chlamydiastatic and paradoxically may play a role both in chlamydial persistence and in protective immunity. Delayed hypersensitivity responses to chlamydiae caused by repeated or persistent infection are thought to be important in the development of the severe scarring sequelae characteristic of cicatricial trachoma and of chronic salpingitis. Chlamydial heat shock proteins bearing close homology with their human equivalents may be major targets for immunopathological responses and their expression is upregulated in IFN gamma induced persistent infection. C. pneumoniae, a common cause of acute respiratory infection in humans, may persist in coronary arteries and is strongly implicated as a risk factor in atherosclerosis and in acute myocardial infarction. This paper reviews the immunology and immunopathology of chlamydial infections in the context of the unique biology of this fascinating but challenging group of organisms.

Animals↗
PubMed1995

A peptide of Chlamydia trachomatis shown to be a primary T-cell epitope in vitro induces cell-mediated immunity in vivo.

Chlamydiae are a major cause of infertility and preventable blindness and there is currently no effective vaccine in humans or rodents against these organisms. We have previously shown that a peptide of 12 amino acids (termed TINKP) from a conserved region of the major outer membrane protein (MOMP) of Chlamydia trachomatis (C. trachomatis) is a primary T-cell epitope in humans. Here we showed that when dendritic cells (DC) from C3H or BALB/c mice were pulsed in vitro with the peptide they stimulated proliferation of syngeneic T cells in vitro indicating that the peptide is also a primary T-cell epitope in mice. Since the skin is a rich source of DC, we immunized mice from each strain with an intradermal injection of the peptide. Humoral and cell-mediated immunity to peptide, MOMP or whole elementary bodies (EB) of C. trachomatis (F/NI1/GU) were assessed. No antibody response to TINKP was observed. However, immunized mice showed recall responses to all three chlamydial antigens. T-cell-mediated immunity in the absence of antibody was induced by a single injection of the peptide intradermally. C. trachomatis isolated from the human genital tract causes salpingitis in mice. Preliminary studies in susceptible C3H mice indicated that intradermal injection of peptide conferred some protection against the development of salpingitis. Thus, a primary T-cell epitope identified by in vitro stimulation using DC can also initiate cell-mediated immunity in vivo and this approach may be useful in the development of vaccines.

Animals↗
PubMed1994

Effect of inhibition of nitric oxide release on the diaphragmatic oxygen delivery-consumption relationship.

PURPOSE: In the vascularly isolated resting and contracting (3 Hz) canine hemidiaphragm, the hypothesis that nitric oxide (NO) is an important regulator of diaphragmatic O2 extraction was tested. METHODS: The effect of an intra-arterial infusion of an NO-synthase inhibitor NG-nitro-L-arginine (L-NA) on the critical O2 delivery (QO2c), below which O2 consumption becomes dependent on O2 supply, was assessed in two groups of animals in which either saline or L-NA (6 x 10(-4) mol/L) was infused into the phrenic artery over 20 minutes. The diaphragm was then perfused either by left femoral arterial blood (autoperfusion) or by pump perfusion with blood from the femoral artery. QO2 was reduced by stepwise hemorrhage in the autoperfusion groups and by reducing the pump rate in the pump perfusion groups. RESULTS: During autoperfusion, QO2c in the saline- and L-NA-treated groups was not different (0.88 +/- 0.15 and 0.98 +/- 0.12 mL/min/100 g, respectively) for the resting diaphragm. Critical O2 extraction ratios were not different (64.5% +/- 9.9% and 67.8% +/- 6.4%, respectively). In the saline group, QO2c during 3-Hz stimulation was 5.03 +/- 0.9 mL/min/100 g. In the L-NA group, diaphragm flow was lower than the saline group, and no QO2c was found. In the pump-perfused contracting diaphragm, QO2c in both groups did not differ (3.1 +/- 0.5 and 4.05 +/- 0.65 mL/min/100 g, respectively). O2 extraction ratios at these O2 deliveries were different (63.3% +/- 5.2% and 77.4% +/- 4.3%, respectively). However, NO-synthase inhibiton had no effect on maximum diaphragmatic O2 extraction ratio. CONCLUSIONS: These results indicate that NO release is an important modulator of the tone of diaphragmatic resistance vessels, but it does not appear to regulate the processes by which O2 extraction is enhanced to compensate for decreased O2 delivery.

Animals↗
PubMed1994

Polymerase chain reaction for the detection of ocular chlamydial infection in trachoma-endemic communities.

Polymerase chain reaction (PCR) with primers derived from the sequence of the cryptic chlamydial plasmid was evaluated for the detection of ocular chlamydial infection in trachoma-endemic populations and was used to explore further the relationship between ocular chlamydial infection and clinical signs of trachoma. It was more sensitive than other laboratory techniques, especially for mild cases of trachoma, in detecting infection in 144 (72%) of 200 who fulfilled the World Health Organization case definition. Of 1132 subjects who did not fulfill these criteria, 85 (7.5%) were PCR-positive, but about one-third of these 85 subjects had minor signs of trachoma. Clinically negative subjects who were PCR-positive were more likely than PCR-negative subjects to have acquired signs of disease at 1 and 6 months of follow-up. Clinical signs were twice as likely to have resolved after 1 month in PCR-negative subjects with disease than in those who were PCR-positive.

Adolescent↗
PubMed1994

Reactivity of antibodies to heteroclitic peptides based on the Chlamydia trachomatis major outer-membrane protein.

One problem of peptide vaccines is that antibodies generated against them react poorly with the target sequence on the native protein. Using monoclonal antibodies (mAbs) to the serovar L1 type-specific epitope on the major outer-membrane protein of Chlamydia trachomatis as our model in conjunction with the Pin Technology Epitope Scanning technique, we had previously identified the critical binding site at this epitope as DAVP. Amino acid substitution showed that AV were essential residues for binding. A series of structurally related (heteroclitic) peptides retaining AV were synthesized. Some of these were found to be much more reactive with the model mAb than peptides of cognate sequence. It was hypothesized that the DAVP peptide only approximated to the conformation of the homologous sequence in the native protein, whereas some of the flexible heteroclitic peptides produced conformations which more closely resembled the native constrained sequence. The key question was whether the most reactive heteroclitic peptide would also generate antibody capable of more efficient binding to the native protein. We therefore immunized mice with one of six heteroclitic peptides or one of two native sequence control peptides. The reactivity of these antisera with the peptide immunogens and with native chlamydial elementary bodies was then evaluated by enzyme immunoassay. Pooled antisera to two of the heteroclitic peptides reacted with significantly greater absorbance (P < 0.05) and at higher dilution with whole chlamydiae than did pooled antisera to the control peptides. This suggests that heteroclitic peptides may in some circumstances be useful to increase the reactivity of site-specific antibodies with epitopes on the native protein important for vaccine development or for serodiagnosis.

Amino Acid Sequence↗
PubMed1994

Regulation of baseline vascular resistance in the canine diaphragm by nitric oxide.

1. The role played by nitric oxide (NO) in the regulation of blood flow to the canine isolated hemidiaphragm was evaluated by determining (a) the effects of the L-arginine analogues NG-nitro-L-arginine methyl ester (L-NAME), NG-nitro-L-arginine (L-NOARG), and argininosuccinic acid (ArgSA) on baseline vascular resistance and of the latter two agents on endothelium-dependent (acetylcholine, ACh) and endothelium independent (sodium nitroprusside, SNP) vasodilatation; (b) the effects of L- and D-arginine on baseline vascular resistance; and (c) the effects of L-glutamine, an inhibitor of intracellular recycling of L-citrulline to L-arginine, on baseline resistance and on the response to ACh and SNP. 2. L-NAME, L-NOARG and ArgSA (6 x 10(-4) M final concentration) increased baseline diaphragmatic vascular resistance to a similar extent (28.6 +/- 4.2%, 26.7 +/- 4.3% and 32.8 +/- 4.6% respectively). L-NOARG and ArgSA reversed the vasodilator effect of ACh but not of SNP. 3. L- and D-arginine had no effect on vascular resistance. 4. L-Glutamine (10(-3) M) increased baseline vascular resistance by 10 +/- 1.9% (P < 0.05) but did not alter responses to either ACh or SNP. 5. Basal NO release plays a role in the regulation of baseline diaphragmatic vascular resistance. L-Arginine analogues tested potently and specifically inhibited this process. Moreover, extracellular L-arginine appears to have no effect on baseline diaphragmatic vascular resistance.

Acetylcholine↗
PubMed1994

Evidence for naturally occurring recombination in the gene encoding the major outer membrane protein of lymphogranuloma venereum isolates of Chlamydia trachomatis.

The nucleotide sequence of the major outer membrane protein gene (omp1) was determined for three geographically distinct lymphogranuloma venereum isolates which were serologically untypeable. The three omp1 sequences were hybrids of serovars L1 and L2, containing a putative DNA recombination site in variable segment 2. Efforts to manipulate the chlamydial genome in vitro by recombination should be intensified.

Amino Acid Sequence↗
PubMed1994

Molecular epidemiology of trachoma in a Gambian village.

The application of a diagnostic and genotyping technique based on the polymerase chain reaction (PCR) to the study of trachoma epidemiology in the Gambian village of Jali is reported. PCR based on the major outer membrane protein (MOMP) gene of Chlamydia trachomatis appears to be more sensitive than either isolation or antigen detection by enzyme immunoassay; it had a specificity of 95% and sensitivity of 51% against clinical signs. PCR genotyping identified genotypes A and B of Chlamydia trachomatis circulating in Jali. Sequencing revealed a Pst1 restriction endonuclease site in the amplified MOMP gene of some B strains but not others; Pst1 digestion of the PCR product proved an easy method of distinguishing these strains. The distribution of serotypes and B strain variants shows a significant degree of household clustering (p < 0.001). PCR based genotyping combined with strain typing provides a new and powerful epidemiological tool for the study of transmission events in trachoma.

Antigens, Bacterial↗
PubMed1994

Systemic and diaphragmatic oxygen delivery-consumption relationships during hemorrhage.

When tissue O2 delivery falls below a critical threshold, tissue O2 uptake (VO2) becomes limited. We compared critical O2 delivery and critical and maximum O2 extraction ratios of the resting and contracting left hemidiaphragm with those of nondiaphragmatic tissues in seven dogs. The left hemidiaphragm was perfused through the left inferior phrenic artery with blood from the left femoral artery. Phrenic venous blood was sampled through a catheter in the inferior phrenic vein. Systemic O2 delivery was reduced in stages by controlled hemorrhage. Left diaphragmatic VO2 during rest and during 3 min of continuous stimulation (3 Hz) of the left phrenic nerve and VO2 of the remaining nonleft hemidiaphragmatic tissues were measured at each stage. Critical diaphragmatic O2 delivery for the resting diaphragm averaged 0.8 +/- 0.16 ml.min-1.100 g-1 with a critical O2 extraction ratio of 65.5 +/- 6%. In the contracting diaphragm, they averaged 5.1 +/- 0.9 ml.min-1.100 g-1 and 81 +/- 5%, respectively. Whole body O2 delivery at which resting diaphragmatic VO2 became supply limited was similar to that for nondiaphragmatic tissues. By comparison, supply limitation of VO2 occurred at a higher systemic O2 delivery in the contracting diaphragm than in the rest of the body despite the increase in critical diaphragmatic extraction ratio. Thus, oxygenation of the isolated diaphragm does not appear to be preferentially preserved during generalized reductions in O2 delivery. These results suggest that, in diseases associated with increased work of breathing and decreased O2 delivery, the diaphragm may become metabolically impaired before limitation of VO2 is observed systemically.

Animals↗
PubMed1994

Pathological O2 supply dependence of diaphragmatic and systemic O2 uptake during endotoxemia.

Our aim was to assess whether endotoxemia impairs the ability of the diaphragm to extract O2 and whether this defect leads to a greater dependence of O2 uptake on O2 delivery. In two groups of anesthetized mechanically ventilated dogs, the left hemidiaphragm was vascularly isolated. Diaphragmatic blood flow and cardiac output (CO) were measured simultaneously in all animals. Saline (S group) or Escherichia coli endotoxin (100 mg; E group) was infused intravenously over 60 min. In both groups, CO was reduced in stages by controlled hemorrhage, and systemic and diaphragmatic O2 deliveries and consumptions were measured at each stage to construct the O2 delivery-O2 consumption relationships. In the S group, the average systemic O2 delivery below which O2 uptake became supply dependent was 7.2 ml.kg-1.min-1. At this O2 delivery, systemic O2 extraction ratio (ER) averaged 67.9%, whereas the maximum O2 ER was 91.3%. Critical diaphragmatic O2 delivery and critical and maximum diaphragmatic O2 ER, by comparison, averaged 9.0 ml.kg-1.min-1, 65%, and 81.9%, respectively. Endotoxin infusion raised critical systemic O2 delivery to 16.7 ml.kg-1.min-1 (P < 0.05) and reduced critical and maximum systemic O2 ER to 55.5 and 77% (P < 0.05), respectively. Similarly, critical diaphragmatic O2 delivery in the E group increased to 14.8 ml.kg-1.min-1 (P < 0.05), whereas critical and maximum O2 ER declined to 51.8 and 72.8%, respectively (P < 0.05). Thus, endotoxemia impairs diaphragmatic O2 extraction. This, in turn, leads to a greater dependence of diaphragmatic O2 uptake on O2 delivery.

Animals↗
PubMed1994

Diaphragmatic pressure-flow relationship during hemorrhagic shock: role of nitric oxide.

In the vascularly isolated resting and contracting (3 Hz) canine hemidiaphragm, we studied the effect of intra-arterial infusion of the nitric oxide (NO) inhibitor NG-nitro-L-arginine (LNA) on the relationship between phrenic arterial perfusion pressure (Pphr) and blood flow (Qphr). In separate groups of animals, either saline or LNA (final concn 6 x 10(-4) M) was infused into the phrenic artery over 20 min. The diaphragm was then autoperfused by diverting flow from the left femoral artery. Arterial blood pressure was reduced in stages by controlled hemorrhage. The Pphr-to-Qphr relationship was plotted for each animal, and the third-order polynomial of best fit was determined by least squares regression. The inflection point of this relationship was determined for each animal. In the contracting and resting diaphragms, the inflection point corresponded to Pphr values of 83.6 +/- 4.7 and 72.5 +/- 6.8 mmHg, respectively, in the saline-treated group compared with 86.2 +/- 2.7 and 76.8 +/- 5.1 mmHg, respectively, in the LNA-treated group. In the contracting diaphragm, LNA reduced Qphr uniformly across the entire range of perfusion pressures. In the resting diaphragm, the effect of LNA was not uniform. At perfusion pressures below the inflection point, the flow was reduced in proportion to the reduction in inflection point flow. At higher perfusion pressures, Qphr was decreased to a greater extent than could be accounted for by the change in inflection point flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

The influence of local antichlamydial antibody on the acquisition and persistence of human ocular chlamydial infection: IgG antibodies are not protective.

In order to study the effect of antichlamydial antibodies in ocular secretions on resistance to ocular chlamydial infection and clearance of this infection, we have performed linked longitudinal studies in a Gambian village in which trachoma is endemic. We have measured IgG and IgA antibody levels to a local serotype B isolate of Chlamydia trachomatis by amplified enzyme immunoassay, and chlamydial antigen levels in conjunctival swabs using a commercially available immunoassay which detects chlamydial glycolipid. Having previously demonstrated that sharing a bedroom with a case of active trachoma is a risk factor for acquisition of the disease, we have analyzed the effect of IgG and IgA antibody on the acquisition and persistence of clinical trachoma after controlling for age, sex, exposure to infection and for the presence of chlamydial antigen using a Poisson regression model. We have found that the presence of antichlamydial IgG in ocular secretions of disease-free subjects is associated with an increased incidence of trachoma. IgA antibody shows an opposite trend, but this is not statistically significant. One possible explanation of these findings is that antichlamydial IgG antibodies enhance the infectivity of C. trachomatis for the human eye; this could have major implications for the development of a chlamydial vaccine.

Adolescent↗
PubMed1993

Genotyping ocular strains of Chlamydia trachomatis by single-tube nested PCR.

A single-tube nested PCR able to discriminate between ocular infection with Chlamydia trachomatis of serovar A, B, or C is described. The method uses genotype-specific primers labeled with different fluorochromes, "drop-in/drop-out" PCR amplification, and product analysis on an Applied Biosystems 373A DNA Sequencer using GENESCAN 672 software. The system readily detected mixed infection with serotypes A and B within the same eye. This strategy provides a rapid genotyping method applicable to a wide variety of epidemiological studies.

Base Sequence↗