Search PubMed⌕ Search

Biomedical subjects

A D Roberts

Publications and source records attributed to A D Roberts.

At least 55 records · Page 3Linked to original sources
PubMed1996

Improving the yield of 2-[18F]fluoro-2-deoxyglucose using a microwave cavity.

We have investigated the use of a microwave cavity (Labwell AB, Sweden) to improve the radiochemical yield of 2-[18F]fluoro-2-deoxyglucose (2-[18F]FDG). After characterizing the heating properties of the cavity, three steps of the Hamacher 2-[18F]FDG synthesis which require heating--azeotropic distillation of the target water, nucleophilic substitution, and hydrolysis of the product--were investigated separately. The average radiochemical yield of 2-[18F]FDG for the microwave synthesis, using the phase transfer reagent tetrabutylammonium bicarbonate, was 62 +/- 4% (72 +/- 5%, decay corrected, synthesis time = 31 min).

Deoxyglucose↗
PubMed1996

An objective evaluation of the effectiveness of different methods of displaying three-dimensional information with medical x-ray images.

RATIONALE AND OBJECTIVES: The authors determine the effectiveness of stereoscopy and vertical-axis rotation for displaying three-dimensional (3-D) information in x-ray images. METHODS: Simple x-ray images were simulated using ray tracing and computer-displayed in monoscopic static (MS), monoscopic rotating (MR), stereoscopic static (SS), and stereoscopic rotating (SR) formats. In two experimental tasks, participants including experts (radiologists and radiographers) were shown images displayed in these four formats. Performance was measured by participants' accuracy of judgment, amount of time taken, and confidence in each response. The experts also informally evaluated the displays using complex fluoroscopic skull images and a simulated diagnostic task. RESULTS: The results from both tasks were consistent and showed MS to be least effective and SR to be most effective on all measures. There was no difference in performance between the nonexperts and experts, whose informal feedback consolidated the experimental findings. CONCLUSIONS: It was found that rotational stereoscopic fluoroscopy is feasible and is an effective way of portraying 3-D information using x-rays.

Computer Simulation↗
PubMed1995

Development of an improved target for [18F]F2 production.

An A1 body target with improved yields of electrophilic [18F]F2 on the Siemens/CTI 11 MeV proton cyclotron at Wisconsin has been developed. The saturation yield is 3.10 +/- 0.40 GBq/microA for beam currents up to 45 microA. The target has routinely produced 20-40 GBq of [18F]F2 for clinical and experimental use over 1600 microA-h operation, with a maximum yield to date of 45.5 GBq (1.2 Ci). Target design, performance and reliability are discussed.

Aluminum↗
PubMed1995

Old mice are able to control low-dose aerogenic infections with Mycobacterium tuberculosis.

Previous work in this laboratory has led to the development of the hypothesis that the increased susceptibility of old mice to tuberculosis infection reflects a limited ability by immune CD4 mediator cells to accumulate at sites of bacterial implantation. To test this hypothesis with very low dose infections, the present study documented the course of a low-dose aerogenic infection with virulent Mycobacterium tuberculosis Erdman against time in the target organs of young (3-month-old) and old (24-month-old) B6D2F1 hybrid mice. The results of the study indicated that the infection was controlled by the two groups of mice at similar rates, although the bacterial load in the old mice was eventually somewhat higher. Despite these similarities, some subtle differences between the young and old mice were also evident and included evidence of increased hematogenous spread of the infection from the lungs to other organs in the old mice. Interestingly, very poor expression of the cytokine interleukin-12 was observed in the lungs of infected old mice, leading to the hypothesis that the poor CD4 response in such animals could be partially attributed to the lack of this Th1-type, CD4 T-cell-enhancing cytokine. In this regard, treatment of old mice with exogenous interleukin-12 increased resistance and promoted gamma interferon secretion by CD4 T cells from these mice, although the effects were generally modest. These data suggest that old mice possess CD4-independent compensatory mechanisms by which to deal with low-dose pulmonary tuberculosis infections, although such mechanisms are less efficient than those seen in young animals.

Aerobiosis↗
PubMed1995

Characteristics of protective immunity engendered by vaccination of mice with purified culture filtrate protein antigens of Mycobacterium tuberculosis.

In this study highly purified culture filtrate proteins obtained from Mycobacterium tuberculosis strains Erdman and H37Rv were tested for their capacity to stimulate immune T cells in vitro, and to immunize mice in vivo. Analysis of the culture filtrate antigen pool revealed a complex mixture of proteins; after separation of this pool into fractions of defined molecular size using an electrophoretic method, it was found that multiple fractions strongly stimulated interferon-gamma (IFN-gamma) secretion by immune CD4 T cells in vitro. In a further series of experiments mice were given multiple immunizations with the culture filtrate protein pool suspended in emulsions of incomplete Freund's adjuvant. Such mice were as resistant as mice given live bacillus Calmette-Guérin (BCG) vaccine to a low dose aerosol challenge infection with M. tuberculosis, but this resistance waned to low levels by 5 months post-vaccination. Furthermore, experiments using the filtrate antigens to boost or augment immunity induced by the BCG vaccination itself were unsuccessful. These data therefore support the hypothesis that the culture filtrate proteins of M. tuberculosis contain multiple antigens that are strongly recognized by T cells acquired during the initial expression of protective immunity to tuberculosis. Conventional immunization with these purified protein antigens can engender a strong degree of protective immunity, but this immunity is apparently not sustained at the same level as that induced by the live vaccine, perhaps suggesting a lack of suitable stimulation of memory immunity.

Animals↗
PubMed1995

The role of interleukin-12 in acquired immunity to Mycobacterium tuberculosis infection.

The early phase of acquired cellular immunity to Mycobacterium tuberculosis infection is mediated by the emergence of protective CD4 T lymphocytes that secrete cytokines including interferon-gamma (IFN-gamma), a molecule which is pivotal in the expression of resistance to tuberculosis. Recent evidence demonstrates that infection with M. tuberculosis induces peripheral blood mononuclear cells to release the cytokine interleukin-12 (IL-12), a molecule that promotes the emergence of T-helper type-1 (Th1), IFN-gamma-producing T cells. We demonstrate here that IL-12 mRNA expression was induced by M. tuberculosis infection both in vivo and in vitro and that exogenous administration of IL-12 to mice transiently resulted in increased resistance to the infection. IL-12 also increased the production of IFN-gamma by both splenocytes derived from infected animals treated in vivo and by antigen-stimulated CD4 cells from untreated infected animals, with maximal effects at times associated with the expansion of antigen-specific CD4 T cells in vivo. In the absence of a T-cell response, as seen in SCID mice or nude mice, IL-12 only slightly augmented the moderate bacteriostatic capacity of these immunocompromised mice. Neutralization of IL-12 by specific monoclonal antibodies resulted in a reduction in granuloma integrity and slowing of the capacity of the animal to control bacterial growth.

Animals↗
PubMed1994

Animal and cell-culture models for the study of mycobacterial infections and treatment.

Emerging problems with the treatment of infections caused by Mycobacterium avium and Mycobacterium tuberculosis require the development of new models, both in vitro and in vivo, in which new chemotherapeutic and immunotherapeutic approaches can be tested. In this brief review, the use of cell culture models, in which drugs can be tested for their capacity to inhibit mycobacterial growth within the infected host macrophage, and new models in vivo in which drugs and/or cytokines can be tested in infected mice are discussed. In this latter case, new emerging mouse models include animals with engineered gene disruptions, in which severely disseminated infections can be produced, thus mimicking events in severely immunocompromised human patients.

Animals↗
PubMed1994

Metabolism of pyruvate and glucose by intact cells of Helicobacter pylori studied by 13C NMR spectroscopy.

The metabolic routes of substrate catabolism by intact cells of H. pylori have been investigated by 13C NMR. Real time analyses of metabolic transformations under anaerobic conditions have been obtained with dense cell suspensions incubated with 13C-labelled pyruvate and glucose. In addition, time point studies have been carried out with cells incubated under aerobic conditions. Anaerobically, pyruvate was rapidly metabolized to lactate, ethanol and acetate. In addition, alanine was produced in significant quantities by cells provided with a nitrogen source and the metabolic incorporation of nitrogen from urea was demonstrated. Under aerobic conditions acetate was the major oxidation product from pyruvate; no evidence was obtained for tricarboxylic acid cycle activity. Glucose was metabolized more slowly than pyruvate. Anaerobically, two major products were observed and identified as sorbitol and gluconate by gas chromatography/mass spectrometry. Evidence was obtained for the oxidation of glucose to acetate under aerobic conditions. The fate of the 13C label with glucose substrates labelled in different positions showed that this oxidation takes place via the Entner-Doudoroff pathway.

Aerobiosis↗
PubMed1993

Cytokine secretion by CD4 T lymphocytes acquired in response to Mycobacterium tuberculosis infection.

The results of this study, in which CD4 T cells were harvested from mice at various times during the course of a virulent Mycobacterium tuberculosis infection and examined for their secretion of cytokines during culture in vitro with bone marrow-derived macrophages presenting mycobacterial Ag, provide evidence for the existence of two separate waves of cytokine-producing CD4 cells. The first, which peaks at the time at which protective immunity was maximally expressed, was characterized as a IFN-gamma-secreting cell population that preferentially recognized macrophages presenting mycobacterial culture filtrate proteins, or that were infected with the live organism. A second population, which emerged 20 to 40 days later at a time when the infection had been contained, secreted IL-4 in response to the filtrate proteins, but also reacted particularly strongly to the 65-kDa (hsp60) heat shock protein molecule of M. tuberculosis. These data indicate that acquired immunity to tuberculosis infection involves the production of both Th1- and Th2-like cell populations that differ in terms of their kinetics of emergence and loss, and in terms of their Ag specificity.

Animals↗
PubMed1993

Evidence for a defective accumulation of protective T cells in old mice infected with Mycobacterium tuberculosis.

Mice infected with virulent Mycobacterium tuberculosis exhibit an age-related increase in susceptibility to disease. The basis of this susceptibility has previously been shown to reflect an inability of the aged host to generate protective CD4 T cells during the early course of the infection. The results of the present study, however, indicate that the emergence of interferon-gamma secreting protective CD4 T cells in such mice is not absent, but merely delayed. Furthermore, flow cytometric analysis of such cells accumulating in the spleens of intravenously infected 24-month-old animals revealed that a large percentage of CD4 cells initially had poor or negative expression of the cell surface markers L-selectin and CD11a, molecules that may be important in the movement of T cells across inflamed endothelial blood vessel surfaces. During the course of the tuberculosis infection the numbers of CD4 cells in the spleens of old mice expressing high levels of these molecules rose to levels similar to those observed in young mice, but by that time the numbers of bacilli in target organs had reached close to fatal levels. These data suggest that the capacity of CD4 cells to cross inflamed endothelial surfaces and home into sites of mycobacterial infection may be deficient in old mice, and hence support the hypothesis that the ensuing delay in accumulating such cells within infected lesions contributes to the increased susceptibility of these animals to disease.

Aging↗
PubMed1993

Inhibition of growth of Mycobacterium avium in murine and human mononuclear phagocytes by migration inhibitory factor.

Infections caused by Mycobacterium avium, the most common form of diseminated bacterial disease in AIDS patients, are difficult to treat because of their resistance to many antimycobacterial drugs. The results of the present study show that recombinant migration inhibitory factor, a 12-kDa molecule recently isolated by COS-1 cell expression screening of cDNA from a human T-cell hybridoma, has potent inhibitory activity on the growth of a panel of clinical isolates of M. avium within both bone-marrow-derived murine macrophages and cultured human blood monocytes. These cells cultured in recombinant migration inhibitory factor exhibit various signs of activation, including cell division, morphological changes such as evidence of substantial phagolysosomal fusion, and enhanced secretion of tumor necrosis factor.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Listeria monocytogenes infection in beta 2 microglobulin-deficient mice.

beta 2 microglobulin-deficient mice, in which the beta 2m gene has been disrupted by homologous recombination, lack functional CD8 T cells and are able to contain but not resolve an intravenous immunizing inoculum of Listeria monocytogenes. We present evidence that compensatory immunity in such immunodeficient mice was mediated by a population of gamma delta T-cell receptor-positive cells; in contrast, neither CD4 cells nor natural killer cells appeared to play any part in this process. These data further support the emerging hypothesis that immune cells other than those bearing the alpha beta T-cell receptor type can also play an important role in acquired resistance to listeriosis.

Animals↗
PubMed1992

T lymphocytes mediating protection and cellular cytolysis during the course of Mycobacterium tuberculosis infection. Evidence for different kinetics and recognition of a wide spectrum of protein antigens.

Recent evidence suggests the existence of at least two pathways of acquired specific resistance to Mycobacterium tuberculosis infection; the first consisting of cytokine-mediated activation of parasitized host cells by protective T cells, and the second involving the lysis of these cells by cytolytic T cells. Evidence presented in this report shows that both of the above mechanisms are operative in experimentally infected mice, but that they differ markedly in terms of their kinetics of emergence and loss. It was found that protective T cell activity was acquired very early during the course of the infection, and was temporally associated with the onset of bacterial elimination; however, cytolytic activity did not peak until 10 to 20 days later. This report shows further that the target Ag of these effector T cell populations were apparently numerous with no evidence for preferential recognition of a few immunodominant Ag. In view of the preponderance of target proteins in the bacterial filtrate, we present the hypothesis that such proteins secreted or otherwise leaked from the dividing mycobacterium are pinocytosed from the phagosome and used by the infected macrophage as the key protective Ag leading to T cell sensitization. This hypothesis thus explains the preferential requirement for the viable bacterium in the generation of specific resistance, and further explains why protective immunity is generated even while the organism is still multiplying in an apparently unrestrained manner.

Animals↗
PubMed1992

Capacity of Mycobacterium avium isolates to grow well or poorly in murine macrophages resides in their ability to induce secretion of tumor necrosis factor.

The results of this study show that clinical isolates of Mycobacterium avium fall into two categories in terms of their capacity to grow within murine bone marrow-derived macrophage cultures: those that grow progressively and those that are incapable of growing within such cells. Members of the first category were invariably of the smooth-transparent colonial type, while most of the second were of the smooth-doomed type. In addition, this paper shows that although all isolates induced tumor necrosis factor (TNF) secretion by host cells to some extent, this production was always delayed in isolates that subsequently grew well in the host cells. This observation, coupled with the demonstration that the growth of the latter isolates was inhibited by the exogenous addition of TNF, leads us to hypothesize that the ability of a given isolate to somehow avoid host macrophage TNF production early during the course of the infection is a key factor in the pathogenesis of the disease.

Animals↗
PubMed1992

Dissemination of enteric Mycobacterium avium infections in mice rendered immunodeficient by thymectomy and CD4 depletion or by prior infection with murine AIDS retroviruses.

This study shows that infection of mice with the murine AIDS virus LP-BM5 or Du5H profoundly depressed the capacity of splenic T cells from these animals to respond to the T-cell mitogen phytohemagglutinin or concanavalin A or to alloantigens. Similar effects were also observed if mice were thymectomized and then infused with monoclonal anti-CD4 antibody (TxCD4- mice). When such mice were infected intravenously with Mycobacterium avium, growth of the infection was markedly exacerbated in the TxCD4- mice or in mice given murine AIDS virus 2 months earlier. In view of these data, we then investigated whether such treatments might cause dissemination of M. avium following enteric implantation of bacteria into the mouse cecum; this route was chosen in an attempt to model events in AIDS patients, in which the gut appears to be one of the major portals of M. avium infection. In this model, the entry and hematogenous dissemination of four clinical isolates of M. avium were monitored against time and found to be accelerated and enhanced in T-cell-deficient mice. In view of this finding, these novel approaches for enteric infection that use immunodeficient mice are presented as potential new models for the evaluation of immunotherapy and chemotherapy in a setting that bears some similarity to events believed to occur in AIDS patients.

Animals↗
PubMed1992

Structural basis of capacity of lipoarabinomannan to induce secretion of tumor necrosis factor.

The results of this study show that lipoarabinomannans (LAM) isolated from a virulent strain and from an avirulent strain of Mycobacterium tuberculosis, which have recently been shown to differ markedly in terms of the structures of their nonreducing termini, also differ markedly in the capacity to induce the secretion of tumor necrosis factor from murine macrophages. It was found that LAM from the avirulent H37Ra strain was 100-fold more potent at inducing tumor necrosis factor secretion than LAM from the virulent Erdman strain, thus leading us to hypothesize that the structure of LAM from a given mycobacterial isolate may directly influence its ability to elicit, or avoid, cytokine-mediated mechanisms of host resistance.

Animals↗