Search PubMed⌕ Search

Biomedical subjects

M G Taylor

Publications and source records attributed to M G Taylor.

At least 19 recordsLinked to original sources
PubMed1992

Non-invasive Doppler ultrasound technique for the in vivo assessment of aortic compliance.

A non-invasive Doppler ultrasound technique for the assessment of aortic compliance is described. This is based on the in vivo measurement of pulse wave velocity along the thoraco-abdominal aortic pathway. A structured protocol has been developed to improve the reproducibility of the technique as well as for the purposes of operator training. Preliminary results of a study of both the intra- and inter-observer variability of the method are provided and problems associated with the technique are discussed. Medical disorders such as atherosclerosis, diabetes mellitus and familial hypercholesterolaemia have all been shown to affect arterial wall compliance. We suggest that the measurement of aortic compliance in vivo may be a useful, non-invasive tool for assessing these patients' susceptibility to atheromatous arterial disease and for monitoring their response to therapy.

Adolescent↗
PubMed1992

Inter-species variation of schistosome 28-kDa glutathione S-transferases.

The 28-kDa glutathione S-transferase from Schistosoma mansoni (Sm28GST) is a candidate vaccine antigen. To evaluate the antigenic and phylogenetic variations between the 28-kDa GSTs from 4 species of schistosome, we have cloned and sequenced the 28-kDa GSTs from Schistosoma haematobium (Sh28GST) and Schistosoma bovis (Sb28GST). Sb28GST and Sh28GST are more similar to each other (97%) than to Sm28GST (90%) and particularly to the 28-kDa GST from Schistosoma japonicum (Sj28GST, 77%). Antisera directed against the major Sm28GST epitopes revealed differences in the recognition of the 28-kDa GSTs from the other schistosome species suggesting that these regions have been subjected to evolutionary pressure. The consequences of such species-specific epitopes on the development of a multi-species anti-schistosome vaccine are discussed.

Amino Acid Sequence↗
PubMed1992

Evaluation of an enzyme linked immunosorbent assay (ELISA) using Schistosoma mansoni soluble egg antigen as a diagnostic tool for Schistosoma mansoni infection in Ethiopian schoolchildren.

Evaluation of the performance of an ELISA test using S. mansoni soluble egg antigens (SEA) in relation to the standard parasitological diagnostic procedure (Kato) was conducted in a specially set up study on 400 Ethiopian schoolchildren. Faecal samples were collected on 3 successive days for preparation of Kato thick smears and two finger prick blood samples were collected onto filter paper from all the children on day 1. All helminth ova present in the triplicate Kato slides were counted and the ELISA test was carried out on both eluted serum samples. Prevalence of infection by Kato was 83.5% in the endemic area and the sensitivity and specificity of the ELISA test were 97.6% and 30.3% respectively, whereas the specificity of the ELISA in the non-endemic area was 95.5%. The main cause of 'false positivity' in the endemic area appeared to be inapparent S. mansoni infection. Because of its high sensitivity, this ELISA test will clearly be of value for seroepidemiological surveys.

Adolescent↗
PubMed1991

6-Mercapto-FAD and 6-thiocyanato-FAD as active site probes of phenol hydroxylase.

Recently, the synthesis and properties of several 6-substituted flavins as active site probes for flavoproteins have been reported (Ghisla, S., Massey, V., and Yagi, K. (1986) Biochemistry 25, 3282-3289). Here, we report results of experiments in which 6-thiocyanato-FAD and 6-mercapto-FAD have been substituted for the native flavin of phenol hydroxylase. The 6-SCN-FAD enzyme was converted spontaneously to the 6-mercaptoflavin form probably due to dissociation of flavin, followed by attack of external protein thiols. The pK alpha values of uncomplexed and phenol-bound 6-mercapto-FAD enzyme were determined. Both the spontaneously formed 6-mercapto-FAD enzyme and the enzyme reconstituted with preformed 6-mercapto-FAD were treated with a variety of thiol-specific reagents, and reaction rates were followed by spectroscopic means. Comparison with the corresponding rates found with free flavin suggested a high degree of accessibility to the flavin 6-position. Accessibility was somewhat decreased in the presence of phenol. Upon treatment with low concentrations of methyl methanethiosulfonate or N-ethylmaleimide (NEM), extremely rapid spectral changes were apparent. The former reaction, however, was reversed spontaneously within 2 h. Reaction with NEM was biphasic, with spectral changes consistent with the mechanism previously proposed (Steenkamp, D. J., McIntire, W., and Kenney, W. C. (1978) J. Biol. Chem. 253, 2818-2824), followed by a small absorbance decrease due to protein conformational changes. The NEM reaction is unusual, being easily reversed by addition of excess dithiothreitol.

Binding Sites↗
PubMed1991

Kinetic and isotopic studies of the oxidative half-reaction of phenol hydroxylase.

Phenol hydroxylase, an FAD-containing monooxygenase, catalyzes the conversion of substituted phenols to the corresponding catechol. Use of metapyrocatechase, capable of dioxygenation of several catechols to give highly absorbing products, permitted determination of the time course of product release from phenol hydroxylase. Product dissociated prior to complete reoxidation of the enzyme, most likely concomitant with formation of the 4a-hydroxyflavin species (intermediate III). Deuterated phenol and thiophenol exhibited no kinetic isotope effect during the oxidative half-reaction. Isotope effects of 1.7 to 3.7 were found with resorcinol for the conversion of the second intermediate to intermediate III. These effects limited the possible models for phenol hydroxylation. An attempt was made to distinguish whether the spectrum of intermediate II is due entirely to that of the flavin moiety of phenol hydroxylase or whether some radical intermediate form involved in the formation of catechol makes a significant visible contribution. Reduced native and 6-hydroxy-FAD phenol hydroxylase were reacted with oxygen and resorcinol in order to provide evidence for the identity of intermediate II.

Isotopes↗
PubMed1990

Biotransformation of intracellular minerals by zinc ions in vivo and in vitro.

Inorganic granules of the general type CaMgP2O7 are found within cells of a wide range of species. The granules are amorphous to X-rays and occur in membrane-bound compartments. They accumulate a variety of cations from the body fluids of these animals. The interaction of zinc ions with pyrophosphate granules from cells of the snail Helix aspersa have been studied in vivo and in vitro by X-ray absorption spectroscopy and X-ray diffraction. The in vivo deposits incorporate zinc and remain amorphous although the pyrophosphate is hydrolysed to orthophosphate. In this in vitro reaction the mineral becomes crystalline but there is little change in the form of the The results clearly indicate a role for the cellular system in maintaining the amorphous state and in the hydrolysis of pyrophosphate to orthophosphate. As such they provide a model system for some of the changes observed in precursors of bone mineral and in pathological changes in the calcification of cartilage.

Animals↗
PubMed1990

Decay of the 4a-hydroxy-FAD intermediate of phenol hydroxylase.

The oxidative half-reaction of phenol hydroxylase involves the formation of three spectrally distinct intermediates (Detmer, K.M., and Massey, V. (1985) J. Biol. Chem. 260, 5998-6005). Addition of an aerobic NADPH-regenerating system, phenol, and azide quantitatively converted oxidized enzyme to the third intermediate, a 4a-hydroxy-FAD species (Detmer, K.M., and Massey, V. (1984) J. Biol. Chem. 259, 11265-11272). This intermediate was isolated in the presence of azide and a wide variety of phenolic ligands. Decay rates were followed for the dehydration of 4a-hydroxy-FAD enzyme resulting in the original oxidized form. Deviation from the rate observed in the absence of phenolic ligands was presumed to be indicative of a binding interaction. Several phenols displayed further stabilization of the 4a-hydroxyflavin species. These ligands exhibited saturation kinetics with respect to the decay half-lives, consistent with a mechanistic model in which both free and bound 4a-hydroxy-FAD enzyme may be directly dehydrated to produce the oxidized species. The lack of stabilization by catechol, the natural product, suggests that product is released from the enzyme during turnover by the time that this intermediate is formed. A pH profile, generated for the decay rates in the absence and presence of phenolic ligand, suggests both acid and base catalysis by hydronium ion and hydroxide, respectively.

Chromatography, Gel↗
PubMed1990

Antibody-dependent killing of Schistosoma mansoni schistosomula in vitro by starch-elicited murine macrophages. Critical role of the cell surface integrin Mac-1 in killing mediated by the anti-Mr 16,000 mAb B3A.

Starch-elicited murine peritoneal macrophages were able to kill schistosomula in vitro in the presence of a variety of immune sera. Dose response experiments revealed the superior "quality" of serum from mice vaccinated four times with highly irradiated cercariae (4xVMS) in mediating killing at titers comparable to the other sera tested. B3A, a partially protective mAb (IgG3) that recognizes a Mr 16,000 schistosomular surface Ag, mediated higher levels of killing than any of the sera at comparable titers. In contrast, H12, a partially protective mAb (IgG2a; anti-Mr 32,000), and C1C9, a nonprotective McAb (IgG3; anti-Mr 38,000) failed to mediate killing. Two anti-Mac-1 alpha-chain mAb (5C6 and M1/70) mediated substantial dose-dependent blocking of 4xVMS and B3A-mediated macrophage killing. In contrast, a mAb to the Mac-1-associated beta-chain was less effective, whereas the mAb F4/80 did not significantly block killing despite being present on this macrophage population. Although whole 5C6 Ig was the most efficient at inhibiting B3A-mediated killing, 5C6 Fab fragments were still effective at concentrations as low as 0.5 microgram/ml (10 nM). On a molar basis 5C6 appeared to be more effective at blocking 4xVMS-mediated killing than M1/70, while only M1/70 was capable of inhibiting macrophage adherence to schistosomula. These findings, together with the observation that anti-alpha chain mAb were far more effective at blocking killing than the anti-beta-chain mAb, rules out the possibility that 5C6 is nonspecifically inhibiting B3A-FcR interaction. The data also imply a functional relationship between Mac-1 and FcRIII, the receptor for B3A, in macrophage killing.

Animals↗
PubMed1990

An online technique for estimating cerebral carbon dioxide reactivity.

A technique for measuring cerebral reactivity using transcranial pulsed Doppler ultrasound is described; the system includes a spectrum analyser and capnometer. Data acquisition and manipulation is under software control. Main stem middle cerebral artery blood velocity is monitored continuously using the transcranial Doppler technique, whilst the operator initiates data collection and controls the inspired gas composition. The calculation of cerebral CO2 reactivity is based upon linear regression analysis of normalized, time-averaged middle cerebral velocity on end-tidal pCO2 and is displayed graphically. Measurement of middle cerebral CO2 reactivities can be completed within 15 min. Results from two subjects, a healthy volunteer and a patient with occlusive disease, are shown to illustrate the technique.

Blood Flow Velocity↗
PubMed1990

The measurement of time-averaged flow by magnetic resonance imaging using continuous acquisition in the carotid arteries and its comparison with Doppler ultrasound.

A continuous acquisition method was used to measure the time-averaged flow in the carotid arteries of 10 normal volunteers, using an interleaved flow-sensitive and flow-compensated field echo sequence on a 1.5 T magnetic resonance (MR) system. Validation of the sequence and technique was performed using a pulsatile rotating phantom. The measured flow rates for the common carotid arteries were compared with Doppler ultrasound values obtained immediately after the MR measurement using a Duplex scanner. The correlation (r = 0.52, P less than 0.01) was significant with data spread accounted for by the inherent errors of both techniques. The difference between time-averaged flow measured by MR and Doppler ultrasound was 1.9%. Short-term reproducibility of each technique was assessed by consecutive measurements with values of 6.8% and 6.6% respectively for MR and Doppler; measurements after a 2 - 4 week interval gave a long-term reproducibility of 11.8% and 9.8% respectively. The advantages of continuous acquisition make the method suitable for non-invasive flow measurements, particularly for vessels that are not accessible to ultrasound.

Blood Flow Velocity↗
PubMed1990

The role of antibody affinity and titre in immunity to Schistosoma mansoni following vaccination with highly irradiated cercariae.

Sera from rabbits and rats vaccinated with highly irradiated cercariae of Schistosoma mansoni (VRabS, VRatS) were found to be of substantially higher affinity than sera from CBA mice vaccinated four times (4 X CVMS), single sex sera (SSS) or chronic infection sera (CIS). In contrast, VRabS and SSS appeared to possess the highest titres of antibody, followed by CIS and VRatS, with 4 X CVMS displaying the lowest titre. Two mouse strains selectively bred for high-affinity (HA) or low-affinity (LA) antibody following vaccination were tested for their ability to resist a challenge infection. LA mice, which produce high titres of low-affinity antibody, manifested significantly more resistance than HA mice, which produce low titres of high-affinity antibody. Immunoprecipitation studies demonstrated that sera from vaccinated LA mice (LVMS) recognized 125I-labelled schistosomular surface antigens more intensely than sera from vaccinated HA mice (HVMS). However, peritoneal macrophages from HA and LA mice in the presence of HVMS, LVMS or 4 X CVMS, and naive macrophages activated in vitro with interferon-gamma (IFN-gamma)/lipopolysaccharide (LPS) mediated comparable levels of schistosomula killing in vitro. The experiments described here provide evidence that the titre of antibody rather than its affinity may be a more critical factor in the development of optimal immunity to S. mansoni.

Animals↗
PubMed1989

Immunity to Schistosoma mansoni in vivo: contradiction or clarification?

In recent years controversy and contradiction have hindered the elucidation of the immune effector mechanisms that are most effective against Schistosoma mansoni - an essential goal for the development of an effective vaccine. However, recent in-vivo studies have clarified the relative contributions of such mechanisms to protection. Here, Dario Vignali and colleagues summarize current evidence that suggests that both antibody and CD4+ T cells, in cooperation with macrophages, are crucial for the development of an effective response. In addition, a model is presented that may account for some of the discrepancies observed and which could be used as a basis for future research.

Animals↗
PubMed1989

Histological examination of the cellular reactions around schistosomula of Schistosoma mansoni in the lungs of sublethally irradiated and unirradiated, immune and control rats.

Histopathological data on the cellular reactions (foci) around Schistosoma mansoni schistosomula in the lungs of both irradiated (750 rad) and unirradiated, passively immunized and normal rats were consistent with the idea that a significant proportion of immune-mediated attrition in passively immunized rats occurs in the lungs. In unirradiated rats, immune serum elicited an enhanced (i.e. larger) and accelerated (i.e. more rapidly developing) inflammatory cellular infiltration around lung-stage parasites when administered 5 days post-infection, when the parasites were already in the lungs. This demonstrated the antigenicity of lung-stage schistosomula and their potential as targets for immune attack. In irradiated rats, innate immunity was decreased as judged by an increase in the number of worms recovered by portal perfusion, and was accompanied by an overall decreased percentage of trapped parasites compared with unirradiated controls, suggesting that trapping in the lungs is involved in innate, as well as acquired immunity. In contrast to the results in unirradiated rats, passive transfer of immune serum into irradiated recipients did not result in larger lung foci than in the NRS-recipients. However, there was evidence of an accelerated response resulting in an essentially similar ratio of trapped parasites (VRS- compared with NRS-recipients) in irradiated rats, as compared with unirradiated rats, reflecting the similar levels of resistance manifested in both groups of rats. This also lent credence to the notion that it was the speed of immune recognition of the migrating schistosomula and the establishment of trapping foci that were of greater importance rather than the size of the enveloping granulomata.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

A role for CD4+ but not CD8+ T cells in immunity to Schistosoma mansoni induced by 20 krad-irradiated and Ro 11-3128-terminated infections.

The role of CD4+ (L3/T4+) and CD8+ (Lyt-2+) T cells in immunity to Schistosoma mansoni induced by 20 krad-irradiated and Ro 11-terminated infections in mice was investigated directly by in vivo depletion of these subsets with cytotoxic rat monoclonal antibodies (mAb). Effective physical depletion was demonstrated by flow cytometric analysis and immunohistochemical staining. Functional depletion of helper activity following anti-CD4 treatment was indicated by an abrogation of concanavalin A(Con A)-induced colony-stimulating factor (CSF) release, while anti-CD8 treatment had no effect in these assays. Pre-existing S. mansoni-specific antibody levels were unaffected by anti-CD4 and anti-CD8 treatment. In vivo depletion of CD4+ T cells resulted in a dramatic reduction in immunity induced by one (up to 100%) and two (up to 70%) vaccinations with 20 krad-irradiated cercariae and also of resistance induced by Ro 11-attenuated infections (up to 100%). Depletion of CD8+ T cells had no effect on resistance induced by any of the vaccination protocols investigated. A correlation was observed between resistance and T cell-induced, macrophage-mediated killing of schistosomula in vitro, both of which were abrogated following anti-CD4 treatment but were unaffected by CD8+ T-cell depletion. The possible role of CD4+ T cells in vivo and the implications for vaccine development are discussed.

Animals↗
PubMed1988

Studies on immunity to Schistosoma mansoni in vivo: whole-body irradiation has no effect on vaccine-induced resistance in mice.

Actively immunized mice, whole-body irradiated with 650 or 525 rad., manifested comparable levels of resistance to Schistosoma mansoni compared with unirradiated, immunized mice in spite of a marked reduction in circulating leucocytes (greater than 90%) and platelets (greater than 85%), and despite an abrogation of delayed-type hypersensitivity (DTH) (Type IV) response to schistosomular antigens (as determined by footpad swelling, 24 h after injection of antigen). However, limited histopathological comparison of lung sections from irradiated and unirradiated mice 7 days post-challenge showed that cellular reactions ('foci') around parasites were essentially similar in size and cellular composition except that in irradiated mice, eosinophils were poorly represented both in the foci and in lung tissue in general. Neither presumed immune complex-mediated (Type III, Arthus reaction) hypersensitivity (as determined by footpad swelling, 5 h after injection of antigen) nor serum anti-schistosomulum extract antibody levels (as determined by ELISA) were affected. In addition, the pattern of 125I-labelled schistosomular surface antigens immunoprecipitated with serum from irradiated and unirradiated mice was essentially similar. These results are consistent with antibody playing an important role in vaccine-induced immunity in mice but suggest that radiosensitive T cell function and radiosensitive cells, such as platelets and polymorphonuclear cells, including eosinophils, may not be essential.

Animals↗
PubMed1988

Comparison of the role of complement in immunity to Schistosoma mansoni in rats and mice.

In vivo depletion of C3 with cobra venom factor (CoF) was used to demonstrate the participation of complement in the innate immunity to S. mansoni and in the acquired immunity of both actively and passively immunized rats. Complement was shown to play an important role in innate immunity, being more involved later in larval migration (Days 8-13 post-infection) than at earlier times (Days--1-3 and Days 3-8 post-infection). Furthermore, the specific component of immunity conferred by immune serum transferred at the lung-migration stage also required complement for optimal expression. This supports the notion that both innate and acquired immunity act not against the much studied early post-penetration stages, but primarily against the lung stages. Although decomplementation at earlier stages of parasite migration (up to 3 days post-infection) did cause some reduction of innate immunity, there was no evidence of any effect on the levels of resistance actively induced by exposure to irradiated cercariae. This suggests that, while complement may play a role in innate immunity during the skin-migration phase, specific complement-mediated attrition does not play a crucial role at this time. The situation was very different in the mouse model, since no involvement of complement in either innate or irradiated vaccine-induced immunity could be demonstrated within the first 15 days of infection. Thus, there appear to be phases in the parasite migration in rats, but not in mice, during which complement becomes a critical factor in both innate and acquired immunity to S. mansoni.

Animals↗
PubMed1987

Serum enzyme changes in calves experimentally infected with Schistosoma bovis.

The activities of the enzymes SD, GD, AAT, 5'NT, GGT, LDH and CPK were determined weekly in sera of two calves each infected with 10,000 S. bovis cercariae and in two controls. In infected animals, LDH activity increased from the first week of exposure and remained high throughout the experiment (22 weeks). GGT activity increased nine weeks after exposure and remained high. CPK activity was elevated during weeks 8-15 of infection. No change was detected in the activity of the other enzymes, nor in any enzymes of the controls.

Animals↗