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Biomedical subjects

A J Grant

Publications and source records attributed to A J Grant.

At least 19 recordsLinked to original sources
PubMed2006

Separation of two cell signalling molecules from a symbiotic sponge that modify algal carbon metabolism.

Two distinct cell signals have been isolated from the sponge host of the tropical sponge/macroalga symbiotic association Haliclona cymiformis/Ceratodictyon spongiosum. These water soluble cell signals (M(r) between 500 and 1000) modify separate steps in the carbon metabolism in both C. spongiosum and the microalga, Symbiodinium from the coral Plesiastrea versipora. The first signal, host release factor (HRF), stimulates the release of compounds derived from algal photosynthesis; the second signal, photosynthesis inhibiting factor (PIF), partially inhibits photosynthesis. Both HRF from the sponge H. cymiformis and HRF from the coral P. versipora stimulated the release of glycerol from Symbiodinium suggesting that they act at a similar step in the metabolism of this alga. This is the first time that such cell signals have been isolated from a sponge. We suggest that they belong to a family of similar cell signals from symbiotic invertebrates that modify algal carbon metabolism.

Animals↗
PubMed2006

A cell signal from the coral Plesiastrea versipora reduces starch synthesis in its symbiotic alga, Symbiodinium sp.

We have previously shown that the coral cell signal, host release factor (HRF) from the scleractinian coral Plesiastrea versipora (Lamarck) stimulates the release of glycerol from its symbiotic dinoflagellate, Symbiodinium sp. Glycerol is a precursor for algal triacylglycerol (TG) and starch, and we have previously observed that HRF reduces the amount of newly synthesized TG in Symbiodinium sp. We have now examined the effect of P. versipora HRF on starch synthesis in isolated Symbiodinium. HRF had no effect on starch synthesis after 2 h photosynthesis (16.3+/-3.0 microg starch per 10(6) algae) compared with algae in seawater (13.9+/-1.2 microg starch per 10(6) algae). However, after 4 h incubation in HRF, there was a reduction (0-76%), in the amount of newly synthesized starch which was correlated with the amount of HRF (10-76 microg/ml). Reducing algal synthesis of both TG and starch in parallel with stimulating glycerol release may provide a mechanism to regulate the population density of intracellular symbiotic algae while still ensuring the transfer of photosynthetically fixed carbon to the animal host in the form of glycerol.

Animals↗
PubMed2004

Aposymbiotic Plesiastrea versipora continues to produce cell-signalling molecules that regulate the carbon metabolism of symbiotic algae.

The scleractinian coral Plesiastrea versipora produces cell signals that regulate the carbon metabolism of its symbiotic algae. Host release factor (HRF) stimulates the release of photosynthate, and photosynthesis inhibiting factor (PIF) partially inhibits carbon fixation in freshly isolated symbiotic algae. Naturally occurring aposymbiotic specimens of P. versipora are rare in Port Jackson, Australia, but one that was collected contained HRF and PIF. Artificially produced aposymbiotic corals of P. versipora that had been kept in the dark for up to 23 months continued to produce both HRF and PIF in the absence of photosynthetically active algae. Aposymbiotic P. versipora from which most of the tissue had been removed, regenerated when they were kept in the dark and fed; the regenerated tissue also contained HRF and PIF. These results suggest that the presence of symbiotic algae is not required for the production of HRF and PIF in P. versipora. We suggest that these cell signals may have evolved in response to symbiosis with Symbiodinium sp. but are now always expressed in the coral P. versipora.

Animals↗
PubMed2003

A symbiosome membrane is not required for the actions of two host signalling compounds regulating photosynthesis in symbiotic algae isolated from cnidarians.

In many cnidarians, symbiotic algae live within host-derived symbiosomes. We determined whether a symbiosome membrane alters the response of isolated symbiotic algae to two signalling compounds that regulate algal carbon metabolism. Host release factor (HRF), which stimulates photosynthate release, and photosynthesis inhibiting factor (PIF), which inhibits photosynthetic carbon fixation, are found in homogenised tissue of the scleractinian coral Plesiastrea versipora. Compared with seawater controls, photosynthate release from isolated algae incubated in P. versipora homogenate for 2 h in the light was: 6 to 19-fold higher from its own algae (free of symbiosomes); 19 to 32-fold higher from Zoanthid robustus algae (within symbiosomes) and 3 to 24-fold higher from Z. robustus algae (free of symbiosomes); and from cultured algae (free of symbiosomes) was seven-fold higher from Montipora verrucosa and four-fold higher from Cassiopeia xamachana. Incubation of algae in P. versipora homogenate inhibited photosynthesis by: 33-49% in P. versipora algae; 29-47% in Z. robustus algae (regardless of whether or not the symbiosome was present); and 25% in M. verrucosa algae. In C. xamachana algae, photosynthesis increased. We conclude that the symbiosome is not essential for, yet does not block, the effects of HRF and PIF.

Animals↗
PubMed2001

An in vitro transposon system for highly regulated gene expression: construction of Escherichia coli strains with arabinose-dependent growth at low temperatures.

Placing a gene of interest under the control of an inducible promoter greatly aids the purification, localization and functional analysis of proteins but usually requires the sub-cloning of the gene of interest into an appropriate expression vector. Here, we describe an alternative approach employing in vitro transposition of Tn Omega P(BAD) to place the highly regulable, arabinose inducible P(BAD) promoter upstream of the gene to be expressed. The method is rapid, simple and facilitates the optimization of expression by producing constructs with variable distances between the P(BAD) promoter and the gene. To illustrate the use of this approach, we describe the construction of a strain of Escherichia coli in which growth at low temperatures on solid media is dependent on threshold levels of arabinose. Other uses of the transposable promoter are also discussed.

Arabinose↗
PubMed2001

MAdCAM-1 expressed in chronic inflammatory liver disease supports mucosal lymphocyte adhesion to hepatic endothelium (MAdCAM-1 in chronic inflammatory liver disease).

Mucosal addressin cell adhesion molecule (MAdCAM-1) plays a pivotal role in T-lymphocyte homing to the gut. Given the strong association between the autoimmune liver diseases primary sclerosing cholangitis and autoimmune hepatitis and inflammatory bowel disease, we investigated the role of MAdCAM-1 in recruiting mucosal lymphocytes to the liver. MAdCAM-1 was strongly expressed on inflamed portal vein/sinusoidal endothelium in autoimmune mediated liver disease. In modified Stamper-Woodruff assays, MAdCAM-1 on hepatic vessels supported adhesion of alpha4beta7+ lymphocytes (i.e., gut-derived T cells) from patients with inflammatory bowel disease and primary sclerosing cholangitis. This adhesion was inhibited by pretreatment with blocking antibodies to MAdCAM-1, alpha4beta7, or the integrin alpha4 chain indicating that MAdCAM-1 in inflamed liver is functionally active. Circulating lymphocytes from patients with primary sclerosing cholangitis showed rolling adhesion on MAdCAM-1 transfectants in a flow-based adhesion assay that could be blocked by anti-MAdCAM-1 or anti-alpha4beta7 mAbs. These findings indicate that, under certain circumstances, vessels in the human liver support adhesion of alpha4beta7+ mucosal lymphocytes via binding to aberrantly expressed MAdCAM-1 on liver endothelium. This provides a mechanism to explain the hepatic recruitment of mucosal lymphocytes in inflammatory liver disease complicating inflammatory bowel disease.

Blood Cells↗
PubMed2000

Responses of olfactory receptor neurons in Utetheisa ornatrix to gender-specific odors.

We recorded the electrophysiological responses of individual olfactory receptor neurons in sensilla trichodea on the antennae of adult arctiid moths, Utetheisa ornatrix, to stimulation with volatiles associated with both sexes. All trichoid sensilla contain at least two receptor neurons, each with distinct action potential amplitudes and waveforms, that respond dichotomously to male and female odors. Although, neither female neuron responds to extracts of coremata or the male-produced pheromone hydroxydanaidal, they do respond in a gender-specific manner to the volatiles emanating from whole pupae, hemolymph, thoracic froth, and adult animals of several ages. Thoracic froth, which contains pyrrolizidine alkaloids, is thought to play a role in defense. Froth from moths reared on diets, with or without added pyrrolizidine alkaloids, were equally effective in eliciting gender-specific patterns of response. Male trichoid receptor neurons respond to these same materials with similar patterns of activation. These receptor neurons provide information about substances, which we have termed "gender odors," that are persistently emitted by nearby animals. These substances do not appear to be the same as those already known to be involved in defense or the sexual dialog between individuals.

Animals↗
PubMed1999

Comparison of three-dimensional visualization techniques for depicting the scala vestibuli and scala tympani of the cochlea by using high-resolution MR imaging.

BACKGROUND AND PURPOSE: Cochlear implantation requires introduction of a stimulating electrode array into the scala vestibuli or scala tympani. Although these structures can be separately identified on many high-resolution scans, it is often difficult to ascertain whether these channels are patent throughout their length. The aim of this study was to determine whether an optimized combination of an imaging protocol and a visualization technique allows routine 3D rendering of the scala vestibuli and scala tympani. METHODS: A submillimeter T2 fast spin-echo imaging sequence was designed to optimize the performance of 3D visualization methods. The spatial resolution was determined experimentally using primary images and 3D surface and volume renderings from eight healthy subjects. These data were used to develop the imaging sequence and to compare the quality and signal-to-noise dependency of four data visualization algorithms: maximum intensity projection, ray casting with transparent voxels, ray casting with opaque voxels, and isosurface rendering. The ability of these methods to produce 3D renderings of the scala tympani and scala vestibuli was also examined. The imaging technique was used in five patients with sensorineural deafness. RESULTS: Visualization techniques produced optimal results in combination with an isotropic volume imaging sequence. Clinicians preferred the isosurface-rendered images to other 3D visualizations. Both isosurface and ray casting displayed the scala vestibuli and scala tympani throughout their length. Abnormalities were shown in three patients, and in one of these, a focal occlusion of the scala tympani was confirmed at surgery. CONCLUSION: Three-dimensional images of the scala vestibuli and scala tympani can be routinely produced. The combination of an MR sequence optimized for use with isosurface rendering or ray-casting algorithms can produce 3D images with greater spatial resolution and anatomic detail than has been possible previously.

Adult↗
PubMed1998

Symptomatic carpal tunnel syndrome after orthotopic liver transplantation: a retrospective analysis.

BACKGROUND: Carpal tunnel syndrome (CTS) is an entrapment neuropathy of the median nerve and has been reported after renal transplantation; there are no reports of CTS after liver transplantation. METHODS: The incidence of and the risk factors for CTS were assessed in 1350 liver allograft recipients. RESULTS: Seventeen women and two men with CTS were identified. Women developed symptoms at a median time of 6.8 months, and all but one received transplants because of primary biliary cirrhosis (PBC). All 17 patients were taking cyclosporine. The only risk factor for CTS was the pretransplant diagnosis of PBC (6.7% of 240 PBC patients surviving 6 months or more compared with 0.4% of 717 patients who received grafts for other indications). CONCLUSIONS: CTS may occur in patients early after liver transplantation; because in many cases the symptoms were attributed to cyclosporine neurotoxicity, the diagnosis should be considered, especially in patients who received grafts because of PBC.

Aged↗
PubMed1996

Electrophysiological responses from receptor neurons in mosquito maxillary palp sensilla.

We recently completed an electrophysiological study of the receptor neurons found in the sensilla basiconica on the maxillary palps of mosquitoes. Our results describe a class of receptor neurons whose properties could provide the afferent input required for some aspects of CO2-modulated host-locating behaviour. First, these neurons have apparent thresholds (150-300 ppm) which are at, or below, the concentration of CO2 (300-330 ppm) normally reported for ambient air. Second, their concentration-response functions are steep, such that small (50 ppm) fluctuations in concentration elicit reliable changes in activity. Third, they behave like absolute CO2 detectors in that their ability to respond to step increases in CO2 concentration is little influenced by the background concentration of CO2. And fourth, a linear extrapolation of the observed response function to the levels that might be expected near vertebrate hosts suggests that these neurons have sufficient dynamic range to cover those CO2 concentrations that should be encountered during a large portion of the behaviour likely involved in host location. The mosquito CO2 receptor neuron thus has an appropriately low threshold and a steep concentration-response function, it is not desensitized by ambient levels of stimulation, and it has a dynamic range appropriate for the distribution of CO2 concentrations expected in the environment. In addition, this sensillum contains two other receptor neurons, neither of which respond to CO2. One of these neurons responds to stimulation with very low doses of another behaviourally relevant compound, 1-octen-3-ol.

Aedes↗
PubMed1995

Synergistic effects of IL-7 and IL-12 on human T cell activation.

We have previously demonstrated that human rIL-12 alone can augment the development of cytotoxic activity in stimulated CD8+ T cells. The present study was undertaken to examine the interactions of rIL-7 and rIL-12 on human peripheral blood T cell activation and CTL differentiation. Purified T lymphocytes were pulsed overnight with immobilized alpha-CD3 and then cultured for 3 additional days with IL-7 and/or IL-12. The combination of IL-7 and IL-12 synergistically enhanced the proliferation of either fresh CD3+ T cells or an IL-2-dependent CD4+ T cell line, Kit-225-K6. This synergy was seen on both subsets of T cells; however, CD8+ T cells were usually more responsive to IL-7 and IL-12 at lower concentrations than were CD4+ T cells. Furthermore, these cytokines additively/synergistically augmented the cytotoxic activity of CD8+ T cells. Abs to IL-2 and IL-2R alpha blocked the synergistic effect on proliferation of CD4+ T cells, but had a minimal effect on the synergistic response of the proliferative and cytotoxic activity of CD8+ T cells. Examination of the effects of IL-7 and IL-12 on the expression of IL-12 receptor on T cells revealed an increase in the subunit of IL-12R by IL-7 as determined by flow cytometric analysis. We analyzed the effects on IFN-gamma production by CD8+ T cells and found that IL-7 alone did not induce detectable levels of IFN-gamma production but together with IL-12 it synergistically enhanced the production of IFN-gamma. We also found that IFN-gamma was probably not required for enhanced CTL activity of CD8+ T cells, because Ab to human IFN-gamma did not block additive/synergistic effects of either cytokine. The synergistic stimulatory activity of IL-7 and IL-12 may be of significance in vivo and may provide an alternative mechanism of stimulating T cells for use in immunotherapy.

Antibodies, Monoclonal↗
PubMed1995

Electrophysiological responses of receptor neurons in mosquito maxillary palp sensilla to carbon dioxide.

Sensilla basiconica on the maxillary palps of female Aedes aegypti contain a receptor neuron which produces a phasic-tonic pattern of action potential response to low concentrations (150-300 ppm) of carbon dioxide (CO2), a stimulus known to be involved with host seeking behavior. These receptor neurons respond reliably to small increments in CO2 concentration (e.g., 50 ppm). We were particularly interested in evaluating the possibility that the sensitivity to step increases in CO2 concentration could be modulated by alterations in the background levels of CO2, over a range which might be encountered during host-seeking behavior. We report here that the response (impulses/s) to a single pulse of a given concentration of CO2 appears to be independent of the background level of CO2, unless that level is equal to or greater than the concentration of the stimulus pulse. Females of other mosquito species, including: Anopheles stephensi, Culex quinquefasciatus, Culiseta melanura, and Aedes taeniorhynchus, also possess sensilla with receptor neurons that respond with comparable sensitivity to CO2 stimulation. However, there is much interspecific variation in both the external morphology of the maxillary palp and the distribution of sensilla along the palp. Male Ae. aegypti have morphologically similar sensilla which also contain a receptor neuron that responds to CO2.

Action Potentials↗
PubMed1994

A lymphokine, provisionally designated interleukin T and produced by a human adult T-cell leukemia line, stimulates T-cell proliferation and the induction of lymphokine-activated killer cells.

In early phases of human T-cell lymphotrophic virus I-induced adult T-cell leukemia (ATL), the malignant cell proliferation is associated with an autocrine process involving coordinate expression of interleukin (IL) 2 and its receptor. However, during late-phase ATL, leukemic cells no longer produce IL-2 yet continue to express high-affinity IL-2 receptors. During studies to define pathogenic mechanisms that underlie this IL-2-independent proliferation, we demonstrated that the ATL cell line HuT-102 secretes a lymphokine, provisionally designated IL-T, that stimulates T-cell proliferation and the induction of lymphokine-activated killer cells. Conditioned medium from HuT-102, when added to the IL-2-dependent CTLL-2 line, yielded a stimulation index of 230. Since CTLL-2 was purported to be IL-2-specific, we performed a number of studies to exclude IL-2 production by HuT-102. Stimulation of CTLL-2 cells by HuT-102-conditioned medium was not meaningfully inhibited by addition of an antiserum to IL-2. Furthermore, uninduced HuT-102 cells did not express mRNA encoding IL-2 as assessed by Northern blot analysis. No biological activity on CTLL-2 cells was mediated by purified IL-1, IL-3, IL-4, IL-5, IL-6, IL-7, IL-9, IL-10, IL-12, IL-13, or granulocyte/macrophage colony-stimulating factor, thus differentiating these factors from IL-T. Based on preliminary biochemical data, IL-T is a protein with a pI value of 4.5 and a molecular mass in SDS gels of 14 kDa. In addition to its action on CTLL-2 cells, 3200-fold-purified IL-T stimulated proliferation of the human cytokine-dependent T-cell line Kit-225. Furthermore, addition of IL-T enhanced cytotoxic activity of large granular lymphocytes (i.e., induced lymphokine-activated killer cells). Thus, IL-T is a lymphokine that plays a role in T-cell proliferation and induction of lymphokine-activated killer cells. Furthermore, IL-T may contribute to IL-2-independent proliferation of select ATL cells and lines.

Animals↗
PubMed1994

The interleukin (IL) 2 receptor beta chain is shared by IL-2 and a cytokine, provisionally designated IL-T, that stimulates T-cell proliferation and the induction of lymphokine-activated killer cells.

Late-phase human T-cell lymphotropic virus I-associated adult T-cell leukemia cells express IL-2 receptors (IL-2R) but no longer produce IL-2. We have reported that the IL-2-independent adult T-cell leukemia line HuT-102 secretes a cytokine, provisionally designated IL-T, that stimulates T-cell proliferation and lymphokine-activated killer cell activity. Stimulation of proliferation of the cytokine-dependent human T-cell line Kit-225 mediated by HuT-102-conditioned medium or by 3200-fold-purified IL-T was not blocked by the addition of antibodies against IL-2 or IL-2R alpha subunit. However, IL-T-mediated stimulation of this human T-cell line was inhibited by addition of Mik-beta 1, an antibody that binds specifically to IL-2R beta subunit. In addition, the activation of large granular lymphocytes to lymphokine-activated killer cells mediated by IL-T-containing conditioned medium was not blocked by antibodies directed toward IL-2 or IL-2 alpha but was inhibited by an antibody to IL-2R beta, suggesting the requirement of this receptor subunit for IL-T action. This conclusion was confirmed using an IL-3-dependent murine myeloid precursor cell line, 32D, that expresses IL-2R alpha and IL-2R gamma, but not IL-2R beta. Neither IL-2 nor IL-T stimulated 32D cell proliferation. However, after transfection with the gene encoding human IL-2R beta, 32D beta cells proliferated on addition of either cytokine. The IL-T-mediated stimulation of 32D beta proliferation was inhibited by an anti-IL-2R beta antibody but not by an anti-IL-2 antibody. Thus, the IL-T-mediated stimulation of T-cell and lymphokine-activated killer cell activation requires the expression of the IL-2R beta subunit.

Animals↗
PubMed1993

Humanized Mik beta 1, a humanized antibody to the IL-2 receptor beta-chain that acts synergistically with humanized anti-TAC.

Mik beta 1 is a mouse mAb directed at the beta-subunit of the human IL-2R (Tac) that inhibits IL-2 binding and inhibits IL-2 induction of large granular lymphocytes (LGL). Mik beta 1 alone does not inhibit IL-2-induced T-cell proliferation, but acts synergistically with anti-Tac to inhibit IL-2-induced proliferation of activated T cells. To evaluate these effects for possible therapy in humans, we constructed two humanized Mik beta 1 antibodies by combining the complementarity-determining regions of the murine antibody with human framework and constant regions. Compared with murine Mik beta 1, the two humanized Mik beta 1 antibodies, which differ in their degree of humanization, had similar affinities for IL-2R beta. The murine Mik beta 1 and one of the humanized Mik beta 1 antibodies were equivalent in competing for IL-2 binding to IL-2R beta and inhibiting IL-2 induction of LGL cytotoxicity. The activity of the second humanized antibody was significantly reduced. The three Mik beta 1 antibodies act synergistically to varying degrees with humanized anti-Tac to prevent IL-2-induced proliferation of activated T cells. This capacity to synergize paralleled their abilities to inhibit IL-2 binding. In addition, both humanized antibodies directed antibody-dependent cell-mediated cytotoxicity. We hope that humanized Mik beta 1 in combination with humanized anti-Tac will provide a new immunosuppressive therapy for the treatment of autoimmune diseases, graft-versus-host disease, and prevention of allograft rejection.

Amino Acid Sequence↗