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R A Wilson

Publications and source records attributed to R A Wilson.

At least 109 records · Page 6Linked to original sources
PubMed1994

Plasmid-coded DNA fragment developed as a specific gene probe for the identification of enteroaggregative Escherichia coli.

Enteroaggregative Escherichia coli (EAggEC) is a recently discovered diarrhoeal pathogen implicated as a cause of persistent diarrhoea in children. EAggEC strains exhibit a characteristic pattern of adherence when incubated with HEp-2 cells. Because of the difficulty in identifying this group of bacteria, the epidemiological significance of this pathogen as a diarrhoeal agent has not been fully realised. A gene probe was developed from the 60-MDa plasmid associated with EAggEC strains that encodes the genes for adherence and fimbriae. The sensitivity of the gene probe was 93% and the specificity 98% for detecting EAggEC isolates and is potentially useful for diagnostic and epidemiological studies.

Bacterial Adhesion↗
PubMed1994

The profile of IgG1 and IgG2a antibody responses in mice exposed to Schistosoma mansoni.

The segregation of IgG2a and IgG1 immunoglobulin isotypes as markers for Th1 and Th2 lymphocytes respectively, was investigated in mice exposed to normal or optimally-irradiated S. mansoni cercariae. Using a panel of ELISAs, soluble antigens from lung-stage schistosomula, adult worms, or eggs, were probed with serum samples collected at biweekly intervals. Infected mice developed increased IgG1 responsiveness to all three antigens, especially between weeks five and seven, whereas IgG2a responses were lower, particularly to egg antigens. This confirms that Th2 responses are dominant after the onset of patency in infected mice. In comparison, vaccinated mice developed lower levels of IgG1, and higher levels of IgG2a to larval and worm antigens. Thus, they had balanced expression of IgG1 and IgG2a, despite having a dominant Th1 lymphocyte population. An elevated IgG1 response to egg antigens in vaccinated mice challenged with normal parasites, occurred two weeks later than in normal mice. Mice exposed to male-only cercariae developed IgG1 and IgG2a antibodies to larval and worm antigens. However, they also had elevated IgG1 to egg antigens from week five, despite a total absence of eggs. Therefore, adult worm antigens may cross react with the egg and stimulate the switch to Th2 dominated responsiveness.

Animals↗
PubMed1994

Hepatic recruitment of mast cells occurs in rats but not mice infected with Schistosoma mansoni.

The pathogenesis of infection with Schistosoma mansoni in rats is distinct from that in mice. Rats are non-permissive hosts and infection is terminated in the liver before egg laying commences whereas the parasites completes its life cycle in mice. Comparison of the mast cell responses in the two species reveals that a pronounced hepatic mastocytosis occurs in the rat and this is concomitant with the demise of the parasite. The majority of recruited hepatic mast cells contain the highly soluble granule chymase, rat mast cell protease-II, which is released systemically into blood during the period of parasite elimination. In contrast, very few mast cells are found in livers of parasitized mice and none contain the soluble granule chymase mouse mast cell protease-1. However, during egg deposition in the gut, an intraepithelial mastocytosis occurs in parasitized mice. These intraepithelial cells are typical mucosal mast cells as determined by their content of mouse mast cell protease-1. Recruitment of mucosal mast cells occurs in the intestinal lamina propria of infected rats soon after the parasites migrate to the liver. These findings suggest that mast cells of the mucosal phenotype are involved in the pathogenesis of the hepatic response to infection in the rat but that, in the mouse, mucosal mastocytosis is associated with intestinal sensitization by egg antigens.

Animals↗
PubMed1994

Noninvasive cardiac testing in the end-stage renal disease patient.

Renal transplant candidates are at increased risk for future cardiac death--approximately 5-10% per year. Invasive testing by coronary angiography has been used to assess the cardiac risk. However this is expensive and carries its own risks to residual renal function as well as cardiac morbidity and mortality. Screening of patients by clinical risk factors may obviate the need for invasive or noninvasive testing in a significant number (approximately 50%) of the renal transplant candidates. Further noninvasive testing with exercise or dipyridamole thallium-201 stress testing in the high-risk patients may be a more cost-effective screening test than coronary angiography. Other noninvasive testing modalities may also prove useful in the future but have not yet been proven in this unique patient population. The characterization of a renal transplant candidate's cardiac risk may assist the clinicians in prioritizing the candidate for transplantation. Recent evidence also suggests that revascularization of the diabetic renal transplant candidate with significant coronary artery disease (which is approachable by angioplasty or bypass surgery) may modify their cardiac risk. Randomized studies of the efficacy of revascularization or medical therapy interventions in the nondiabetic renal transplant candidate with coronary artery disease have not been performed.

Coronary Disease↗
PubMed1993

Pulmonary T helper lymphocytes are CD44hi, CD45RB- effector/memory cells in mice vaccinated with attenuated cercariae of Schistosoma mansoni.

Percutaneous exposure of C57Bl/6 strain mice to radiation-attenuated schistosome cercariae stimulates proliferation of Ag-specific T lymphocytes in the draining lymph nodes (LN), followed by an intense leukocytic infiltration into the pulmonary parenchyma and airways. The airway T cells persist at elevated levels at least up to 10 wk and will secrete IFN-gamma and IL-3 upon antigenic stimulation in vitro. We report here that more CD4+ T cells from the airways responded rapidly to mitogen by up-regulating the p55 subunit of the IL-2R than did splenocytes from the same animal, suggesting that the bulk of the pulmonary Th infiltrate comprised previously activated cells. A four-fold higher response to Ag indicated the greater abundance of schistosome-specific cells in the lungs than the spleen. Virtually all of the pulmonary CD4+ T cells expressed high levels of the memory marker CD44 (Pgp-1), in contrast with the situation in the draining LN and circulation where only a minority were in that category. Very few Th cells from the inflamed lung bound antibody to an epitope coded for by the B exon of CD45, unlike those from the LN and circulation; the antibody normally binds strongly to naive and weakly to memory CD4+ T cells. Overall, the airway CD4+ T lymphocytes in the schistosome-vaccinated mouse display the functional and phenotypic characteristics of short-term effector/memory cells. We believe that their presence endows the lung with the ability to respond rapidly to recall Ag in the form of challenge parasites.

Animals↗
PubMed1993

Selective etching of AlAs for preparation of III-V semiconductor thin foils.

A new method of thin section preparation of III-V semiconductors and multilayers for transmission electron microscopy (TEM) is presented that exhibits considerable advantages over conventional methods such as ion beam milling and jet thinning. GaAs thin films and multilayers of GaAs/In chi Ga1-chi As/GaAs are grown over an etch release layer of AlAs on GaAs substrates by molecular beam epitaxy (MBE). Planar TEM sections prepared by selective etching from these samples show improved ability to image film morphology and dislocation arrangements, and the resulting large thin electron transparent areas facilitate dislocation density measurements and detection of spatial variations. Avoidance of radiation effects and wedge shaping, both common to ion milled samples, allows this method to be used to prepare uniform thickness standards of single layer GaAs films for EDS analysis or lattice imaging.

Aluminum↗
PubMed1993

Fractionation of schistosome antigens by high performance electrophoretic chromatography and their screening for the ability to induce Th1 lymphocyte activity.

The technique of high performance electrophoretic chromatography (HPEC) has been used to fractionate soluble antigens from adult Schistosoma mansoni worms on the basis of molecular weight (MW), prior to screening for their ability to stimulate T lymphocyte activity. Approximately 250 micrograms of protein were separated by continuous electrophoresis through an SDS polyacrylamide gel into 30-50 aqueous samples of minimal volume (80 microliters). Each consecutive sample contained a limited number of proteins of progressively greater MW, although the resolution of the fractionation was affected by a number of factors including acrylamide concentration, gel length, gel diameter and electrophoretic current. Following the extraction of SDS using Calbiosorb resin, the aqueous fractions were used directly to stimulate cultures of lymphocytes taken from the lymph nodes of infected or vaccinated mice. The most promising fractions were those containing proteins which induced the release of high levels of interferon-gamma relative to the extent of proliferation. This suggests that these proteins are good inducers of Th1 lymphocyte activity.

Animals↗
PubMed1993

Diagnostic accuracy of seismocardiography compared with electrocardiography for the anatomic and physiologic diagnosis of coronary artery disease during exercise testing.

A multicenter study was performed to compare the diagnostic accuracy of a new technique, seismocardiography, with that of electrocardiography for physiologically and anatomically significant ischemic coronary artery disease (CAD) during exercise stress testing. Five participating centers enrolled 129 patients who had simultaneous seismocardiograms and 12-lead electrocardiograms at the time of their exercise treadmill stress tests. Two different definitions of CAD were used: anatomic and physiologically significant disease. The presence of anatomically significant CAD (> or = 50% diameter stenosis) was documented by coronary angiography. Physiologically significant CAD was defined as present in the same 129 patients when coronary arteriography (> or = 50% diameter stenosis) and thallium-201 scintigraphy (defect on initial postexercise images) were both abnormal. Seismocardiography had a significantly better sensitivity for detecting anatomic CAD than did electrocardiography (73 vs 48%; p < 0.001), without loss of specificity (78 vs 80%; p = NS). Exercise seismocardiography added significant incremental diagnostic information beyond that provided by exercise electrocardiography. Seismocardiography was more sensitive (without less specificity) in women and in patients who did not achieve maximal predicted heart rate. In patients with physiologically significant CAD, the seismocardiogram was also significantly more sensitive (78%) than was the electrocardiogram (55%) (p < 0.02), without loss of specificity (84 vs 74%). Seismocardiography significantly improved sensitivity for the detection of anatomic and physiologic CAD. It is easy to perform and may be a clinically useful adjunct in exercise stress testing.

Coronary Angiography↗
PubMed1993

Clonal relationships and variation in virulence among Escherichia coli strains of avian origin.

Average genetic relatedness among 44 Escherichia coli strains of serotypes O1, O2, and O78 isolated mainly from birds with colibacillosis or swollen-head syndrome from France or Saudi Arabia was estimated based on allelic variation detected by multilocus enzyme electrophoresis. For 20 enzyme-encoding loci, we resolved 2.8 alleles per locus and distinguished 17 electrophoretic types (ETs) that were used to mark naturally occurring cell lineages or clones. On average, ETs differed at 37% of their loci. Forty-eight percent of the isolates represent three ETs, two of which belong to previously defined complexes of clones identified in avian disease in North America and Europe. Virulence of strains, assessed in experimental infections of day-old chicks, showed little variation among isolates of a clone, but was significantly variable among isolates of different clone complexes. These findings add support to the evidence that a majority of avian isolates that cause colibacillosis belong to a few cosmopolitan pathogenic clones and indicate a substantial between-clone component of pathogenicity.

Alleles↗
PubMed1993

Mechanical features and in vivo imaging of a polymer stent.

A polyethylene-terephthalate (PETP, polyester), self-expanding, braided mesh stent has been developed for percutaneous (coronary) arterial implantation. In vitro measurements showed that the radial pressure delivered by this device was similar to a self-expanding, stainless steel stent. Due to hysteresis-like behaviour, it proved necessary to mount the polymer stent on the delivery system immediately before the placement procedure, and to select a diameter in the unconstrained condition, which was 60% larger than the diameter of the target vessel. Eight polyester stents were implanted in peripheral arteries of four pigs. Except for heparin during the implantation procedure, antithrombotic or antiplatelet drugs were not administered. After four weeks repeat angiography revealed that one of the stents was subtotally occluded. At autopsy, two other stents proved to be located in the aortic bifurcation, probably due to failure of the delivery system. Quantitative angiographic assessment showed that the mean luminal diameters at the site of stent placement were 3.3 +/- 0.2 mm before, 3.2 +/- 0.2 mm immediately after, and 2.7 +/- 0.5 mm at four weeks after implantation. Intravascular ultrasound (IVUS) examination after 4 weeks could identify the individual struts of the stents, as well as their length. In addition, a description of the extent of neointimal hyperplasia was feasible. The IVUS assessment was validated by histological examination. In conclusion, polyester stents can be constructed with mechanical properties similar to stainless steel stents. After implantation in porcine peripheral arteries, five of six correctly placed stents were patent at four weeks. Imaging of stents by angiography and IVUS provided complementary information.

Angiography↗
PubMed1993

Phase image analysis of anomalous ventricular activation in pediatric patients with preexcitation syndromes or ventricular tachycardia.

This prospective study evaluated the accuracy of phase analysis of scintigraphic imaging in defining the site of earliest ventricular activation in pediatric patients with electrophysiologic disorders. Twenty patients (10.8 +/- 5.5 years) with preexcitation (n = 16) or ventricular tachycardia (VT) (n = 4) were independently evaluated by phase image analysis and endocardial catheter mapping. The earliest phase angle (contraction), which was common to three scintigraphic imaging planes during preexcited sinus rhythm or VT, was compared with the earliest retrograde atrial activation during reciprocating tachycardia or the origin of VT, as defined by catheter mapping. Phase analysis of earliest contraction was concordant with catheter mapping of electrical activation in all 13 free-wall accessory connections and in three of four patients with VT. Inconclusive definition of activation occurred only in paraseptal accessory connections or VT. In conclusion, phase analysis accurately defines anomalous ventricular activation that is due to free-wall accessory connections or VT. In patients with complex anatomy or small size, phase analysis allows noninvasive localization of the anatomic substrates of tachycardia.

Adolescent↗
PubMed1993

Clonal diversity among strains of Escherichia coli incriminated in turkey colisepticemia.

The extent of genetic differentiation among 80 Escherichia coli isolates collected from turkeys with acute colisepticemia was assessed based on allelic variation at 20 enzyme-encoding loci detected by multilocus enzyme electrophoresis. Isolates were polymorphic at 17 loci and were classified into 32 multilocus genotypes, delineating clones, that differed on average at 36% of the loci. In the total sample, 29 (36%) of the isolates belonged to one of two closely related clones, differing only in a single electromorph, and 11 of these isolates were serogroup O78. Most isolates fell into one of 4 genetically distinct clusters of strains. Three of these clusters represent E. coli clone complexes that have been previously identified in avian diseases and a fourth cluster which is specific to colisepticemia in turkeys. Most (73%) isolates produced aerobactin, whereas none produced hemolysins. Assays for detecting K1 capsules, including the use of polyclonal antisera, monoclonal antibodies, and K1-specific bacteriophages, gave variable results, but showed that overall 18% of the strains from colisepticemia were K1 encapsulated with most of the K1+ isolates found in one clone cluster. The results show that many cases of colisepticemia in turkey flocks are caused by a small number of pathogenic clones representing at least three distinct clone complexes.

Animals↗
PubMed1993

Characteristics of Vero cytotoxin producing Escherichia coli associated with intestinal colonization and diarrhea in calves.

Isolates of Escherichia coli which produce Vero cytotoxin (VTEC) were obtained during 1983-1989 from calves raised in 5 north-central states of the USA. All of the calves experienced intestinal epithelial colonization by VTEC, diarrhea or both; twelve of the calves had bloody diarrhea. Twenty one isolates were serogroup O111 and the others were O103, O69, O45, 026, O5, or non-typable (4 isolates). All but one of the isolates hybridized with the CVD419 probe which identifies most VTEC strains. Thirty two isolates hybridized with the VT1 probe, 3 with both the VT1 and VT2 probes, and one with neither probe. The culture filtrate of the VT probe negative isolate was partially neutralized by SLT I monoclonal antibody. For the other isolates, the results of toxin neutralization by anti-SLT I and anti-SLT II monoclonal antibodies corresponded exactly with the VT1 and VT2 probe hybridization results. Three of the strains adhered in a localized manner to HEp-2 cells and Intestine 407 cells.

Animals↗
PubMed1993

Immunity and immunoregulation in helminth infections.

Parasitic helminths continue to be a major cause of morbidity in human populations, particularly in the tropics and subtropics. The need for effective vaccines that minimize worm burdens, thus reducing associated pathology, is evident. With this goal in mind, an intense research effort is in progress to characterize immune responses to helminths, especially in the context of recent developments in our understanding of the cytokine network. The growing realization that the parasites can themselves subvert host immune responses to their own advantage makes the task of vaccine development that much harder.

Animals↗
PubMed1993

Protein synthesis and release by cultured schistosomula of Schistosoma mansoni.

The lung schistosomulum of Schistosoma mansoni is the target of protective immunity in mice singly vaccinated with irradiated cercariae. Since the effector responses are T cell-mediated, their initiation requires the release of antigens from the intact parasite. We have used the technique of biosynthetic labelling with [35S]methionine, before and after transformation of the cercariae, to analyse the kinetics of protein synthesis and release by the schistosomulum. In addition, the proteins present in the soluble fraction of the parasite and those released during in vitro culture have been characterized. During a 7-day culture period schistosomula derived from labelled cercariae lost proteins most rapidly within the first 3 h after transformation. Two proteins of molecular weight 61 and 20 kDa were dominant and may correspond to areas of proteolytic activity. Analysis of the rate of protein synthesis of schistosomula labelled after transformation revealed four different phases, which may relate to the developmental processes occurring in vivo. During the first 24 h, synthesis was very low, increasing to a plateau and then rising to a peak at day 8; therefore the rate declined rapidly. Whilst some stage-specific synthesis of proteins was detected in the soluble fractions of the parasite bodies, the pattern of proteins released by cultured larvae was remarkably uniform. At least 15 proteins were detected by autoradiography with bands at 61, 45 and 20 kDa being particularly prominent. These proteins merit further study as potential mediators of the protective immune response.

Animals↗
PubMed1993

Immunity to Schistosoma mansoni in mice vaccinated with irradiated cercariae: cytokine interactions in the pulmonary protective response.

In C57BL/6 strain mice vaccinated with attenuated cercariae of Schistosoma mansoni, the major site of immune elimination of challenge parasites is the lungs. We have monitored pulmonary events after both vaccination and challenge by bronchoalveolar lavage, and examined the profile of cytokines released by recovered cells upon stimulation with larval antigens in vitro. From 14 days post-vaccination, lavage samples contain infiltrating lymphocytes which produce abundant interferon-gamma (IFN-gamma) and interleukin-3 (IL-3). We suggest that the lymphocytes recruited to the lungs are effector/memory cells of the Th1 subset. Challenge of vaccinated mice results in a second influx of IFN-gamma- and IL-3-secreting cells into the airways, earlier than after vaccination alone, or in appropriate controls. Ablation studies reveal that CD4+ T cells are the source of the IFN-gamma. The timing of cytokine production after both vaccination and challenge coincides with phases of macrophage activation already recorded, and with the presence of parasites in the lungs. Administration of monoclonal antibody directed against IFN-gamma, over the period of challenge elimination, almost completely abrogates protection in vaccinated mice, but does not affect the ratio of Th1:Th2 cells in the lungs. Immunity in this model is not, however, affected by inhibition of nitric oxide production, or neutralization of TNF. We suggest that the effector mechanism may operate by blocking parasite migration, and that loss of protection following neutralization of IFN-gamma may be attributed to changes in composition, density and cohesiveness of pulmonary foci.

Animals↗
PubMed1993

Negative inotropy of lidocaine: possible biochemical mechanisms.

Previous studies have shown that lidocaine has a negative inotropic effect on the myocardium. This effect could be mediated by a decrease in O2 supply and/or utilization, or abnormalities in intracellular Ca2+ handling by the myocardium. To investigate which of these mechanisms are involved we studied nine open-chest anaesthetized pigs, which received an infusion of lidocaine (4-16 mg.min-1) in the left anterior descending coronary artery (LADCA), sufficient to induce a severe depression of the regional myocardial function. Biopsies for high energy phosphate levels were obtained from both the LADCA and control regions before and during the infusion. After measurements at peak lidocaine dose, the hearts were rapidly excised for harvesting of LADCA, and control region sarcoplasmic reticulum (SR) vesicles for in vitro measurements of Ca2+ uptake rate. During lidocaine infusion, coronary blood flow increased (23%), while ATP, Ca2+ uptake by the SR and percentage segment length shortening decreased by 20%, 19% and 30% respectively. However, O2 consumption in the LADCA region did not differ before or during lidocaine infusion (102 +/- 20 and 104 +/- 29 ml.min-1, respectively). Hence, lidocaine in doses sufficient to depress regional myocardial function does not decrease O2 supply, but decreases the efficiency of oxygen utilization. Although we cannot entirely rule out the possibility that blockade of fast sodium channels is a contributory factor, the observed decrease in the tissue level of ATP and the rate of Ca2+ uptake by the SR may be related to the negative inotropic action of lidocaine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine Nucleotides↗