Search PubMed⌕ Search

Biomedical subjects

J McFadden

Publications and source records attributed to J McFadden.

At least 19 recordsLinked to original sources
PubMed2006

Mycobacterium bovis BCG as a delivery system for the RAP-1 antigen from Babesia bovis.

Babesia bovis is the causative agent of babesiosis, a tick-borne disease that is a major cause of loss to livestock production in Latin America. Vaccination against Babesia species represents a major challenge against cattle morbidity and mortality in enzootic areas. The aim of this study was to evaluate the capacity of Bacille Calmette-Guerin (BCG) to deliver the rhoptry associated protein (RAP-1) antigen of B. bovis and to stimulate specific cellular and humoral immune responses in mice. Two of five mycobacterial expression vectors efficiently expressed the antigen. These constructs were subsequently studied in vivo following three immunization protocols. The construct with the greatest in vivo stability proved to be the one that induced the strongest immune responses. Our data support the hypothesis that specific T lymphocyte priming by rBCG can be employed as a component of a combined vaccine strategy to induce long-lasting humoral and cellular immune responsiveness towards B. bovis and encourage further work on the application of rBCG to the development of Babesia vaccines.

Animals↗
PubMed2006

Photopatch testing of 1155 patients: results of the U.K. multicentre photopatch study group.

BACKGROUND: Photoallergic contact dermatitis can be difficult to diagnose if not appropriately investigated. Currently, the most common U.K. photoallergens appear to be sunscreen chemicals. The investigation of choice is photopatch testing (PPT), which is probably underused. In part, this is due to differences in methodology and results interpretation. OBJECTIVES: To conduct PPT using a group of sunscreen chemicals, defined indications and a standardized methodology including interpretation and relevance of reactions in patients attending for investigation at 17 centres across the U.K., Ireland and the Netherlands. METHODS: Patients (n = 1155) who fulfilled the inclusion criteria were investigated with PPT using sunscreen chemicals in addition to suspected topical products. Readings were taken at 24, 48 and 72 h following standardized ultraviolet A irradiation (5 J cm(-2)). The clinical relevance of any reaction was recorded. RESULTS: Of the 1155, 130 had allergic reactions (11.3%). Of these, 51 had photoallergy (PA) (4.4%), 64 had contact allergy (CA) (5.5%), and 15 patients had combined PA and CA (1.3%). Multiple PA was seen in some. The most common photoallergen was benzophenone-3 (27 reactions; 21%). Most reactions (60%) were clinically relevant. The most common indication for testing in patients found to have PA was a history of reacting to a sunscreen (41%). The other 59% had an exposed-site dermatitis/skin problem or a photodermatosis. Some centres (n = 8) performed readings after the standard 48-h reading, and an extra 32 PA and 22 CA reactions were detected, which were not evident at 48 h. A new photoallergen (octyl triazone) was detected in two patients. CONCLUSIONS: Sunscreen PA and CA are probably equally uncommon. Most reactions, of both reaction types, were relevant clinically. A large proportion of patients (59%) found to have PA was unaware of reacting to a sunscreen chemical, suggesting that PA should be considered as an explanation in any exposed-site dermatitis. Although this study focused on reactions at 48 h postirradiation, readings performed up to 96 h, while inconvenient, add value by detecting additional relevant responses. A previously unknown photoallergen was found, highlighting the need for awareness of novel photoallergens in the marketplace. A standardized PPT method not only encourages more use of this investigation, but also facilitates comparison of results between centres and so will improve our understanding of PA.

Adolescent↗
PubMed2005

Compiling a molecular inventory for Mycobacterium bovis BCG at two growth rates: evidence for growth rate-mediated regulation of ribosome biosynthesis and lipid metabolism.

An experimental system of Mycobacterium tuberculosis growth in a carbon-limited chemostat has been established by the use of Mycobacterium bovis BCG as a model organism. For this model, carbon-limited chemostats with low concentrations of glycerol were used to simulate possible growth rates during different stages of tuberculosis. A doubling time of 23 h (D = 0.03 h(-1)) was adopted to represent cells during the acute phase of infection, whereas a lower dilution rate equivalent to a doubling time of 69 h (D = 0.01 h(-1)) was used to model mycobacterial persistence. This chemostat model allowed the specific response of the mycobacterial cell to carbon limitation at different growth rates to be elucidated. The macromolecular (RNA, DNA, carbohydrate, and lipid) and elemental (C, H, and N) compositions of the biomass were determined for steady-state cultures, revealing that carbohydrates and lipids comprised more than half of the dry mass of the BCG cell, with only a quarter of the dry weight consisting of protein and RNA. Consistent with studies of other bacteria, the specific growth rate impacts on the macromolecular content of BCG and the proportions of lipid, RNA, and protein increased significantly with the growth rate. The correlation of RNA content with the growth rate indicates that ribosome production in carbon-limited M. bovis BCG cells is subject to growth rate-dependent control. The results also clearly show that the proportion of lipids in the mycobacterial cell is very sensitive to changes in the growth rate, probably reflecting changes in the amounts of storage lipids. Finally, this study demonstrates the utility of the chemostat model of mycobacterial growth for functional genomic, physiology, and systems biology studies.

Culture Media↗
PubMed2001

Expression of the B-cell and T-cell epitopes of the rabies virus nucleoprotein in Mycobacterium bovis BCG and induction of an humoral response in mice.

Expression vectors containing rabies virus nucleoprotein B-cell and T-cell epitopes in Mycobacterium bovis BCG were constructed. The epitopes were subcloned into the M. leprae 18-kDa gene to ensure correct presentation to the host immune system. Expression of the 18-kDa::B+T epitope fusion protein was driven by either the hsp60 promoter, which is constitutively activated at a high level in M. bovis BCG, or the 18-kDa promoter, which is strongly induced in vivo. Mice were immunised intra-peritoneally with the recombinant BCG cultures and compared to a control group vaccinated with the commercial rabies vaccine Rai-SAD. Both of the expression vectors elicited a higher antibody titre than that of the rabies vaccine, with the highest response shown by M. bovis BCG (pUP203), expression controlled by the 18-kDa promoter. Immunisation with M. bovis BCG (pUP202), expression controlled by the hsp60 promoter, resulted in a continuously increasing antibody titre up to 60 days post immunisation. The mice antibodies were also capable of recognising the whole rabies virus and not only the synthetic peptide epitopes.

Animals↗
PubMed2001

Antigen 43, the major phase-variable protein of the Escherichia coli outer membrane, can exist as a family of proteins encoded by multiple alleles.

agn43 encodes a major phase-variable outer-membrane protein, antigen 43 (Ag43), involved in autoaggregation of Escherichia coli cells. The gene is present in single copy on the chromosome of E. coli K-12. In contrast, Southern hybridization and gene inactivation studies demonstrate that control producer strain E. coli ML308-225 possesses duplicate copies of agn43 (agn43A and agn43B). Construction and analyses of single and double knockout mutants clearly show that both alleles are capable of expressing antigen in a phase-variable manner, with observed differences in the ON<-->OFF switch frequencies appearing to favour expression of Ag43B under conditions of normal laboratory growth. Comparative analysis of agn43A and agn43B gene sequences revealed 98% identity at the nucleotide and predicted protein levels, with differences in the protein sequence of the surface-expressed alpha(43) subunit altering the surface probability of one of the predicted epitopes. Analysis of a panel of enteropathogenic E. coli strains by Southern hybridization using agn43-specific gene probes provided strong evidence for the presence of varying numbers of agn43 alleles within clinical isolates. Taken together, the results indicate the presence of a family of distinct Ag43 proteins encoded by multiple chromosomal alleles.

Adhesins, Bacterial↗
PubMed2000

Deletion of the putative antioxidant noxR1 does not alter the virulence of Mycobacterium tuberculosis H37Rv.

SETTING: The cloned M. tuberculosis noxR1 gene has been shown to confer resistance to reactive nitrogen intermediates (RNI) and reactive oxygen intermediates (ROI) upon Escherichia coli and Mycobacterium smegmatis. OBJECTIVE: To investigate the role of noxR1 in resistance to RNI and virulence of M. tuberculosis. DESIGN: The noxR1 gene was deleted from M. bovis BCG and M. tuberculosis H37Rv by allelic exchange. The mutants were compared to wild type strains with respect to resistance to chemically generated RNI. The virulence of the M. tuberculosis mutant was investigated in a murine model of infection. RESULTS: The NoxR1 mutants grew normally in Sautons and 7H9 broths. The BCG mutant demonstrated decreased resistance to in vitro generated RNI compared to the wild type. Resistance to RNI could be restored to the mutant by reintroduction of the noxR1 locus on a replicating plasmid. However, deletion of noxR1 from M. tuberculosis H37Rv did not result in decreased resistance to RNI nor a difference in growth and survival of the bacterium during murine infection. CONCLUSION: The noxR1 gene locus in M. bovis BCG bestows ability to resist RNI generated in vitro. In M. tuberculosis H37Rv, however, noxR1 is either not involved in RNI resistance and virulence or is better compensated for by other mechanisms.

Animals↗
PubMed1999

Global distribution of crustal magnetization discovered by the mars global surveyor MAG/ER experiment

Vector magnetic field observations of the martian crust were acquired by the Mars Global Surveyor (MGS) magnetic field experiment/electron reflectometer (MAG/ER) during the aerobraking and science phasing orbits, at altitudes between approximately 100 and 200 kilometers. Magnetic field sources of multiple scales, strength, and geometry were observed. There is a correlation between the location of the sources and the ancient cratered terrain of the martian highlands. The absence of crustal magnetism near large impact basins such as Hellas and Argyre implies cessation of internal dynamo action during the early Naochian epoch ( approximately 4 billion years ago). Sources with equivalent magnetic moments as large as 1.3 x 10(17) ampere-meter2 in the Terra Sirenum region contribute to the development of an asymmetrical, time-variable obstacle to solar wind flow around Mars.

Journal Article↗
PubMed1999

A quantum mechanical model of adaptive mutation.

The principle that mutations occur randomly with respect to the direction of evolutionary change has been challenged by the phenomenon of adaptive mutations. There is currently no entirely satisfactory theory to account for how a cell can selectively mutate certain genes in response to environmental signals. However, spontaneous mutations are initiated by quantum events such as the shift of a single proton (hydrogen atom) from one site to an adjacent one. We consider here the wave function describing the quantum state of the genome as being in a coherent linear superposition of states describing both the shifted and unshifted protons. Quantum coherence will be destroyed by the process of decoherence in which the quantum state of the genome becomes correlated (entangled) with its surroundings. Using a very simple model we estimate the decoherence times for protons within DNA and demonstrate that quantum coherence may be maintained for biological time-scales. Interaction of the coherent genome wave function with environments containing utilisable substrate will induce rapid decoherence and thereby destroy the superposition of mutant and non-mutant states. We show that this accelerated rate of decoherence may significantly increase the rate of production of the mutated state.

Adaptation, Physiological↗
PubMed1999

Lichenoid tissue reaction in porphyria cutanea tarda.

We report a patient presenting with lichenoid plaques on exposed skin who had the metabolic features of porphyria cutanea tarda (PCT). Histology of lesional skin demonstrated a lichenoid inflammatory cell infiltrate in the upper dermis, while direct immunofluorescence revealed immunoreactive colloid bodies. Monochromator irradiation testing demonstrated photosensitivity in the visible spectrum consistent with porphyria. Solar-simulated irradiation induced a papular reaction with lichenoid histological changes. We propose that this atypical presentation of PCT may reflect a lichenoid tissue response to a porphyrin-mediated photochemical reaction.

Facial Dermatoses↗
PubMed1999

Intercellular IgA dermatosis (IgA pemphigus)--two cases illustrating the clinical heterogeneity of this disorder.

IgA pemphigus is rare but may be underdiagnosed. We describe two cases, a 50-year-old female with a pustular eruption resembling subcorneal pustular dermatosis and a 55-year-old male with a pruritic vesiculopustular eruption simulating dermatitis herpetiformis. They illustrate the clinical heterogeneity of IgA pemphigus which is likely to reflect differences in autoantigens, analogous to pemphigus vulgaris and pemphigus foliaceus. There is now evidence that IgA pemphigus encompasses at least two subgroups: a subcorneal pustular dermatosis (SPD)-type, (see case 1) characterized by subcorneal pustules and autoantibodies to desmocollin 1; and intra-epidermal neutrophilic dermatosis (IEN)-type cases (see case 2) which show intra-epidermal pustules and in whom the autoantigen may be desmoglein 3, the pemphigus vulgaris antigen.

Anti-Inflammatory Agents↗
PubMed1999

Stimulation of transposition of the Mycobacterium tuberculosis insertion sequence IS6110 by exposure to a microaerobic environment.

The Mycobacterium tuberculosis-specific insertion sequence IS6110/986 has been widely used as a probe because of the multiple polymorphism observed among different strains. To investigate transposition of IS6110, a series of artificially constructed composite transposons containing IS6110 and a kanamycin resistance marker were constructed. The composite transposons were inserted into a conditionally replicating, thermosensitive, Escherichia coli-mycobacterial shuttle vector and introduced into M. smegmatis mc2155. Lawns of transformants were grown at the permissive temperature on kanamycin-supplemented agar and subsequently prevented from further growth by shifting to the non-permissive temperature. Under normal atmospheric conditions, kanamycin-resistant papillae appeared after only about 5-6 weeks of incubation. However, these events were not associated with transposon mobilization. In contrast, lawns that were exposed to a 48 h microaerobic shock generated kanamycin-resistant papillae after only 6-14 days. These events were generated by conservative transposition of the IS6110 composite transposon into the M. smegmatis chromosome, with loss of the shuttle vector. In common with other IS3 family elements, transposition of IS6110 is thought to be controlled by translational frameshifting. However, we were unable to detect any significant frameshifting within the putative frameshifting site of IS6110, and the level of frameshifting was not affected by microaerobic incubation. The finding that transposition of IS6110 is stimulated by incubation at reduced oxygen tensions may be relevant to transposition of IS6110 in M. tuberculosis harboured within TB lesions.

Adaptation, Physiological↗
PubMed1998

Lunar surface magnetic fields and their interaction with the solar wind: results from lunar prospector

The magnetometer and electron reflectometer experiment on the Lunar Prospector spacecraft has obtained maps of lunar crustal magnetic fields and observed the interaction between the solar wind and regions of strong crustal magnetic fields at high selenographic latitude (30 degreesS to 80 degreesS) and low ( approximately 100 kilometers) altitude. Electron reflection maps of the regions antipodal to the Imbrium and Serenitatis impact basins, extending to 80 degreesS latitude, show that crustal magnetic fields fill most of the antipodal zones of those basins. This finding provides further evidence for the hypothesis that basin-forming impacts result in magnetization of the lunar crust at their antipodes. The crustal magnetic fields of the Imbrium antipode region are strong enough to deflect the solar wind and form a miniature (100 to several hundred kilometers across) magnetosphere, magnetosheath, and bow shock system.

Journal Article↗
PubMed1998

Magnetic Field and Plasma Observations at Mars: Initial Results of the Mars Global Surveyor Mission

The magnetometer and electron reflectometer investigation (MAG/ER) on the Mars Global Surveyor spacecraft has obtained magnetic field and plasma observations throughout the near-Mars environment, from beyond the influence of Mars to just above the surface (at an altitude of approximately 100 kilometers). The solar wind interaction with Mars is in many ways similar to that at Venus and at an active comet, that is, primarily an ionospheric-atmospheric interaction. No significant planetary magnetic field of global scale has been detected to date (<2 x 10(21) Gauss-cubic centimeter), but here the discovery of multiple magnetic anomalies of small spatial scale in the crust of Mars is reported.

Journal Article↗
PubMed1998

Mycobacterial DNA not detected in liver sections from patients with primary biliary cirrhosis.

BACKGROUND/AIMS: Recent studies in primary biliary cirrhosis have reported the detection of serum antibodies against Mycobacterium gordonae and of mycobacterial DNA in liver sections. The aim of this study was to investigate whether mycobacterial DNA is present in liver biopsy material in primary biliary cirrhosis. METHODS: Archival liver biopsy specimens from 11 patients with primary biliary cirrhosis (10 female, mean age 52 years) and 11 patients with autoimmune hepatitis (10 female, mean age 53 years) were identified. Positive control tissue comprised five archival lymph node specimens from patients with tuberculous lymphadenopathy, three of which had stained positive on ZN staining, and also a liver biopsy specimen from a patient with tuberculous hepatitis (ZN positive). Fixed sections were deparaffinised and DNA was extracted by mechanical disruption with glass beads. DNA was purified by use of diatoms and lysis in guanidinium thiocyanate in a technique previously validated for archival DNA. Primers were directed to amplify a partial 16S ribosomal RNA gene yielding the species-specific character for mycobacteria, and also to amplify the constitutively-expressed human gene GAPDH. RESULTS: The polymerase chain reaction was shown to be capable of detecting 1 fg of M. gordonae DNA in 'spiked' samples, equivalent to 1-5 bacterial cells. No mycobacterial DNA was detected in liver biopsy samples from either the primary biliary cirrhosis or autoimmune hepatitis groups. Of the tuberculous control sections, mycobacterial DNA was detected in four of five lymph nodes and the liver biopsy specimen. GAPDH amplification was detected in all tested samples from liver disease and tuberculous control samples. CONCLUSION: These data do not support a role for mycobacteria in the aetiology of primary biliary cirrhosis.

Adult↗
PubMed1997

Escape from evolutionary stasis by transposon-mediated deleterious mutations.

Evolution within a rugged fitness landscape is limited by the tendency for organisms to become trapped on local optima resulting in evolutionary stasis. It is presently unclear how founder populations escape from an adaptive peak to found a new species. Insertion sequences, transposons and other mobile DNA elements are found in all species of eukaryotes, bacteria and archaebacteria, where they have been sought and are usually considered to be genomic parasites or selfish genes. However, many transposons and other mobile repetitive DNA are remarkably species or phyla-specific, indicating that infection with transposable elements coincides with speciation events and is involved in promoting evolutionary change. We propose here a model in which transposable elements are involved in speciation events by their ability to produce irreversible deleterious mutations that promote escape from evolutionary stasis. We have constructed a genetic algorithm designed to model both spontaneous and transposon-mediated mutations in populations of asexual digital organisms. We use this model to investigate the effect of transposon-mediated mutations on the rate of evolution of digital organisms as they compete for resources within an artificial adaptive landscape. In the absence of transposon mutations the seed organisms quickly evolve to occupy the nearest adaptive peak but thereafter evolutionary stasis ensues and adjacent empty peaks are left unoccupied. In the presence of transposon mutations, evolution is again dominated by stasis but is punctuated by bursts of rapid evolution in with consecutive unoccupied adaptive peaks are filled with organisms derived from single transposition events. Rapid evolutionary events leading to founding of new biological species, may be similarly initiated by irreversible deleterious mutations induced by transposition.

Adaptation, Physiological↗
PubMed1997

Interlaboratory evaluation of a human patch test for the identification of skin irritation potential/hazard.

The human 4 hr patch test provides an opportunity to identify substances with significant skin irritation potential without recourse to the use of animals. To demonstrate the validity of the method it must be relevant and reliable. It is self-evident that the method is relevant to the identification of skin irritation hazards to humans. However, it is essential that the results be reproducible. This paper presents data on a number of substances tested by different laboratories. Eight substances were tested by two or more laboratories and the data compared with a standard positive control, 20% sodium dodecyl sulfate. In almost all cases, the outcome of this comparison was identical. Thus, despite the fact that there is known variability among human subjects in terms of skin reactivity to irritants, this simple method showed good reproducibility for the classification of acute skin irritation potential. Therefore, it is argued that this human 4-hr patch test is a valid alternative to the equivalent rabbit test for the assessment of skin irritation hazard to humans.

Adult↗