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Biomedical subjects

L Guan

Publications and source records attributed to L Guan.

At least 37 records · Page 2Linked to original sources
PubMed1999

Dose dependence of CTL precursor frequency induced by a DNA vaccine and correlation with protective immunity against influenza virus challenge.

Intramuscular injection of BALB/c mice with a DNA plasmid encoding nucleoprotein (NP) from influenza virus A/PR/8/34 (H1N1) provides cross-strain protection against lethal challenge with influenza virus A/HK/68 (H3N2). CTL specific for the H-2Kd-restricted epitope NP147-155 are present in these mice and are thought to play a role in the protection. To assess the effectiveness of NP DNA immunization in comparison with influenza virus infection in the induction of CTL responses, we monitored the frequency of CTL precursors (CTLp) in mice following i.m. injection with NP DNA or intranasal infection with influenza virus and showed that the CTLp frequency in NP DNA-immunized mice can reach levels found in mice that had been infected with influenza virus. We also measured the CTLp frequency, anti-NP Ab titers, and T cell proliferative responses in mice that were injected with titrated dosages of NP DNA and documented a correlation of the CTLp frequency and the Ab titers, but not proliferative responses, with the injection dose. Furthermore, we observed a positive correlation between the frequency of NP147-155 epitope-specific CTLp and the extent of protective immunity against cross-strain influenza challenge induced by NP DNA injection. Collectively, these results and our early observations from adoptive transfer experiments of in vitro activated lymphocytes from NP DNA-immunized mice suggest a protective function of NP-specific CTLp in mice against cross-strain influenza virus challenge.

Animals↗
PubMed1999

Toward a cancer therapy with boron-rich oligomeric phosphate diesters that target the cell nucleus.

The viability of boron neutron capture therapy depends on the development of tumor-targeting agents that contain large numbers of boron-10 (10B) atoms and are readily taken up by cells. Here we report on the selective uptake of homogeneous fluorescein-labeled nido-carboranyl oligomeric phosphate diesters (nido-OPDs) by the cell nucleus and their long-term retention after their delivery into the cytoplasm of TC7 cells by microinjection. All nido-OPDs accumulated in the cell nucleus within 2 h after microinjection. However, nido-OPDs in which the carborane cage was located on a side chain attached to the oligomeric backbone were redistributed between both the cytoplasm and nucleus after 24 h of incubation, whereas nido-OPDs in which the carborane cage was located along the oligomeric backbone remained primarily in the nucleus. Furthermore, cell-free incubation of digitonin-permeabilized TC7 cells with the nido-OPDs resulted in nuclear accumulation of the compounds, thus corroborating the microinjection studies. Our observation of fluorescence primarily located in the cell nucleus indicates that nuclear-specific uptake of sufficient amounts of 10B for effective boron neutron capture therapy ( approximately 10(8)-10(9) 10B atoms/tumor cell) via nido-OPDs is achievable.

Biological Transport↗
PubMed1999

Temperature can alter the function outcome of spinal cord regeneration in larval lampreys.

Now that spinal cord regeneration has been demonstrated in mammals [Bregman B. S. et al. (1995) Nature 378, 498-501; Cheng H. et al. (1996) Science 273, 510-513], we must examine the consequences and look for means of avoiding negative outcomes. The larval lamprey, which readily regenerates cut spinal axons, offers a model for this important next step. In the present study, one group of larval lampreys with spinal lesions was kept at room temperature during recovery. Another group was returned to their usual cold room temperature. A majority of animals kept at room temperature recovered full locomotor behavioral function, while a majority of those that recovered at a colder temperature exhibited dysfunctional locomotor behavior. The dysfunction most often consisted of segments rostral and caudal to the lesion site lacking the usual coordination and apparently interfering with each. In both groups, there was a close association between the presence of dysfunction and the quality of the intersegmental coordination as assessed in the isolated spinal cord preparation. These results suggest that a relatively minor difference in conditions under which an animal recovers may drastically alter the likelihood of a favorable functional outcome.

Animals↗
PubMed1999

Epileptiform activity can be initiated in various neocortical layers: an optical imaging study.

The initiation site for triggering epileptiform activity was investigated via optical imaging using voltage-sensitive dyes in the neocortical slice perfused with artificial cerebral spinal fluid containing nominally zero magnesium. The neocortical slices (400-microm thick) were harvested from Sprague-Dawley rats (P21-28). Optical imaging was made by using a high speed photodiode array. Spontaneous epileptiform activity emerged 20-40 min after the preparation was perfused with zero-magnesium solution. There was a good correspondence between electrical and optical signals (n = 46), although the details of the two recordings were somewhat different. The initiation sites were measured optically in 11 preparations. Among them, four were found to be located in superficial layers, two were found in middle layers, and five were found in deep layers. Repeated recordings revealed that these initiation sites were relatively stable; shifting of the initiation site was not observed. Therefore spontaneous epileptiform activity could be initiated in various cortical layers, from layer I to layer VI. The activation started from a small area <0.04 mm(3) and spread smoothly from the initiation site to adjacent cortical areas, suggesting that the initiation site is very confined to one of the cortical layers. The initiation sites were distributed randomly in various cortical areas, and no higher probability was found in a special cortical region. Electrical stimulation delivered via a glass microelectrode filled with 2 M NaCl (2-5 MOhms) could reliably trigger epileptiform activity that had the same characteristics as the spontaneous activity. The cortical neurons activated directly by the stimulation were around the electrode's tip and estimated to be within a 50-microm area, suggesting that only a few neurons were needed to form an initiation site. Because the timing for stimulation was arbitrary and the evoked events were initiated independent of discharges of neurons in any other layers, it is likely that the initiation site for epileptiform activity in various cortical layers is independent of the control of layer V pyramidal neurons. Together these finding suggest that the epileptiform focus is confined and can be formed in several (probably all) neocortical layers and in many cortical areas. The initiating neurons may be of different types because neuronal types in various cortical layers are different.

Animals↗
PubMed1998

Homogeneous immunoconjugates for boron neutron-capture therapy: design, synthesis, and preliminary characterization.

The application of immunoprotein-based targeting strategies to the boron neutron-capture therapy of cancer poses an exceptional challenge, because viable boron neutron-capture therapy by this method will require the efficient delivery of 10(3) boron-10 atoms by each antigen-binding protein. Our recent investigations in this area have been focused on the development of efficient methods for the assembly of homogeneous immunoprotein conjugates containing the requisite boron load. In this regard, engineered immunoproteins fitted with unique, exposed cysteine residues provide attractive vehicles for site-specific modification. Additionally, homogeneous oligomeric boron-rich phosphodiesters (oligophosphates) have been identified as promising conjugation reagents. The coupling of two such boron-rich oligophosphates to sulfhydryls introduced to the CH2 domain of a chimeric IgG3 has been demonstrated. The resulting boron-rich immunoconjugates are formed efficiently, are readily purified, and have promising in vitro and in vivo characteristics. Encouragingly, these studies showed subtle differences in the properties of the conjugates derived from the two oligophosphate molecules studied, providing a basis for the application of rational design to future work. Such subtle details would not have been as readily discernible in heterogeneous conjugates, thus validating the rigorous experimental design employed here.

Animals↗
PubMed1998

Induction of MHC class I-restricted CTL response by DNA immunization with ubiquitin-influenza virus nucleoprotein fusion antigens.

DNA vaccines have been shown to be an effective means of inducing cytotoxic T-lymphocyte (CTL) responses in both young and aged mice. Better understanding of the pathways by which antigens encoded by DNA vaccines are processed and presented to CTL may allow for improvements in CTL responses in older animals. Since CTL recognize short peptides presented by MHC class I molecules, and since ubiquitin-dependent proteolysis is widely believed to be responsible for degradation of endogenously synthesized antigens and generation of these peptide ligands, we sought to use ubiquitin (Ub) conjugation to target influenza virus nucleoprotein (NP) antigen into the Ub-proteasome degradation pathway for MHC class I-restricted antigen processing and presentation. However, the addition of the Ub moiety did not affect the half-life of Ub-NP protein in transiently transfected human rhabdomyosarcoma (RD) cells. Moreover, the modifications of NP DNA vaccine with Ub conjugation did not affect their ability to induce a CTL response specific for the H-2Kd-restricted NP147-155 epitope, as assessed by both percent cytolysis in bulk CTL culture and by CTL precursor (CTLp) frequency in limiting dilution analysis (LDA). In contrast, the anti-NP antibody (Ab) responses were dramatically reduced in mice immunized with low doses (1 microgram) of Ub-NP constructs, compared with mice immunized with wild-type NP DNA. These results demonstrate that Ub conjugation alone does not guarantee targeting of endogenously synthesized antigens for rapid degradation by proteasomes. Furthermore, the ability of ubiquintination to reduce Ab responses to NP without affecting CTL responses suggests that the Ub modifications result in a lower availability of full-length NP from transfected cells in vivo. The implications of these data on antigen presentation and cross-priming are discussed.

Animals↗
PubMed1998

Molecular characterization of the putative T-cell receptor cavity of the superantigen staphylococcal enterotoxin B.

A number of investigators have utilized a variety of methods to identify the structural basis for the interaction of superantigens with the T-cell receptor beta-chain. The previous studies strongly suggest that a region of the toxin near residues N23, Y61, Y91 and D209 is important for this binding activity. Examination of crystal structure data shows that these residues line the rim of one side of a shallow cavity in the toxin. In an attempt further to define the face of the staphylococcal enterotoxin B (SEB) molecule involved in the interaction with the beta-chain, we have employed a polymerase chain reaction (PCR)-based, site-specific mutagenesis method to generate amino acid substitutions of residues on the opposite side of this putative T-cell receptor interaction cavity. Our results show that Y175 and N179 appear to be involved in the function of this superantigen, since each of several substitutions at this position exhibits a significantly reduced ability to induce T-cell proliferation. At the same time, mutation of the proximal Y186 does not alter the superantigen activity of SEB. Binding analysis of these mutants shows that class II binding activity is not significantly altered. Analysis of the responding T cells shows that the mutant toxins maintain T-cell receptor V beta selectivity. However, responses of T cells bearing the V beta 8.1 allele appear to be particularly diminished. When viewed in the context of other results reported in the literature, our results suggest that the T-cell receptor interaction site involves SEB residues which ring both the Y175/N179-side and the N23-side of a cavity on one side of the toxin molecule.

Alleles↗
PubMed1998

Two structurally similar maize cytosolic superoxide dismutase genes, Sod4 and Sod4A, respond differentially to abscisic acid and high osmoticum.

The maize (Zea mays) superoxide dismutase genes Sod4 and Sod4A are highly similar in structure but each responds differentially to environmental signals. We examined the effects of the hormone abscisic acid (ABA) on the developmental response of Sod4 and Sod4A. Although both Sod4 and Sod4A transcripts accumulate during late embryogenesis, only Sod4 is up-regulated by ABA and osmotic stress. Accumulation of Sod4 transcript in response to osmotic stress is a consequence of increased endogenous ABA levels in developing embryos. Sod4 mRNA is up-regulated by ABA in viviparous-1 mutant embryos. Sod4 transcript increases within 4 h with ABA not only in developing embryos but also in mature embryos and in young leaves. Sod4A transcript is up-regulated by ABA only in young leaves, but neither Sod4 nor Sod4A transcripts changed in response to osmotic stress. Our data suggest that in leaves Sod4 and Sod4A may respond to ABA and osmotic stress via alternate pathways. Since the Sod genes have a known function, we hypothesize that the increase in Sod mRNA in response to ABA is due in part to ABA-mediated metabolic changes leading to changes in oxygen free radical levels, which in turn lead to the induction of the antioxidant defense system.

Abscisic Acid↗
PubMed1998

Protective CD4+ and CD8+ T cells against influenza virus induced by vaccination with nucleoprotein DNA.

DNA vaccination is an effective means of eliciting both humoral and cellular immunity, including cytotoxic T lymphocytes (CTL). Using an influenza virus model, we previously demonstrated that injection of DNA encoding influenza virus nucleoprotein (NP) induced major histocompatibility complex class I-restricted CTL and cross-strain protection from lethal virus challenge in mice (J. B. Ulmer et al., Science 259:1745-1749, 1993). In the present study, we have characterized in more detail the cellular immune responses induced by NP DNA, which included robust lymphoproliferation and Th1-type cytokine secretion (high levels of gamma interferon and interleukin-2 [IL-2], with little IL-4 or IL-10) in response to antigen-specific restimulation of splenocytes in vitro. These responses were mediated by CD4+ T cells, as shown by in vitro depletion of T-cell subsets. Taken together, these results indicate that immunization with NP DNA primes both cytolytic CD8+ T cells and cytokine-secreting CD4+ T cells. Further, we demonstrate by adoptive transfer and in vivo depletion of T-cell subsets that both of these types of T cells act as effectors in protective immunity against influenza virus challenge conferred by NP DNA.

Animals↗
PubMed1998

Initiation of spontaneous epileptiform activity in the neocortical slice.

Cortical local circuitry is important in epileptogenesis. Voltage-sensitive dyes and fast imaging were used to visualize the initiation of spontaneous paroxysmal events in adult rat neocortical slices. Although spontaneous paroxysmal events could start from anywhere in the preparation, optical imaging revealed that all spontaneous events started at a few confined initiation foci and propagated to the whole preparation. Multielectrode recording over hundreds of spontaneous events revealed that often two or three initiation foci coexisted in each preparation (n = 10). These foci took turns being dominant; the dominant focus initiated the majority of the spontaneous paroxysmal events during that period. The dominant focus and dynamic rearrangement of foci suggest that the initiation of spontaneous epileptiform events involves a local multineuronal process, perhaps with potentiated synapses.

Action Potentials↗
PubMed1998

The influence of stress on edentulous maxillary bone with different artificial anterior tooth arrangements by three-dimensional photoelasticity.

OBJECTIVE: To investigate the influence of stress on edentulous maxillary bone different artificial anterior tooth arrangements, with the goal to establish theoretical evidence for optimal anterior tooth arrangements in complete denture restoration. MATERIALS AND METHODS: Three-dimensional photoelasticity experimental stress analysis was conducted. Shear stresses were measured and principal stresses were separated into six different models of maxillary central incisor arrangements. RESULTS: The value of maximum stresses and the absolute values of principal stresses and positive stresses were obtained. The distribution curve of shear stresses and principal stresses was also shown. CONCLUSIONS: The horizontal distance between the incisive papilla center and the incisal margin of the maxillary central incisor should be no more than 8 mm, if the anterior mandibular arch is larger than the maxillary arch. The principal stress is a better indicator of stress on edentulous maxillary bone when load is applied at the protrusive occlusal position.

Alveolar Process↗
PubMed1998

[Infection of cryptosporidium in child patients with diarhea in Changsha].

Fecal specimens were collected from 102 outpatients with diarrhea in Children's Hospital from March to October, 1997. The fecal smears were examined for cryptosporozoites with the rapid modified acid-fast two-step methods. The positive rate was 4.90%(5/102). There was no significant difference between female and male (P > 0.05). The positive rates of 1-month-, 5-year-, and 10-year-old groups were 4.05% (3/74), 7.14%(1/14), and 7.14(1/14), respectively. We conclude that there is crytosporidium infection in child patients with diarrhea in different sex and age groups.

Adolescent↗
PubMed1998

[Study of a new type of material substituted for human hard tissues-hydroxyl poly calcium sodium phosphate: histologic report implants in mandible of animals].

This study was aimed to evaluate the histocompatibility of hydroxyl poly calcium sodium phosphate (HPPA) preliminarily. HPPA and hydroxylapatite were implanted in the mandibular defect in dogs. The implant-bone interface was observed by using stereomicroscope and decalcified histologic sections. The result demonstrates that HPPA has well-osseous integrated property after being implanted into bone tissues. This suggests that HPPA might be a new material of future excellence in substitution for human hard tissues.

Animals↗
PubMed1998

[The changes in quantities of elements around cementum-dentin junction in human natural tooth--electron probe microanalysis].

To study the changes of inorganic and organic substance around cementum-dentin junction in the tissues of human natural tooth, the method of electron probe microanalysis was used in this research project. Determinations of weight percentage (wt%) were made for Ca, P and S elements around cementum-dentin junction. The results showed that the changes in quantities of Ca, P and S elements around cementum-dentin junction were not significant(P > 0.1). These suggest that the quantities of inorganic and organic substance have not obviously varied with the anatomic structure of natural tooth.

Adult↗
PubMed1997

Inhibition of T cell superantigen responses following treatment with the kappa-opioid agonist U50,488H.

Previous work in our laboratory has shown that cytokine production by primary murine macrophages, and macrophage cell lines, is inhibited following treatment with the kappa-opioid agonist U50,488H. Furthermore, we have found that the participation of both accessory cells and T cells in an antibody response is suppressed by this compound. We have utilized the superantigen staphylococcal enterotoxin B (SEB) to further examine the effects of U50,488H on accessory and T cell function. The results showed that the proliferative response of lymph node T cells to SEB presented by activated macrophages was significantly inhibited by the kappa-opioid agonist at concentrations as low as 100 nM. However, suppression of the T cell response to SEB presented by resting macrophages required 100 times the concentration of U50,488H. On the other hand, the production of IL-2 in response to lymph node T cell stimulation with SEB was not altered by the opioid treatment. Additional experiments utilizing the opiate antagonist naloxone and the kappa-selective antagonist nor-binaltorphimine (norBNI) were performed in order to further characterize the opioid receptor involved in the suppressive activity of U50,488H. Results showed that both naloxone and norBNI were able to block the inhibitory activity of U50,488H. Further analysis showed that the proliferative response of thymic T cells was more sensitive to the effects of U50,488H, and the response with both activated and resting macrophages was suppressed. In addition, the production of IL-2 by the thymic T cells was also inhibited by the opioid treatment. The mechanism of suppression of superantigen-induced T cell responses is discussed.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1997

Mutations affecting the superantigen activity of staphylococcal enterotoxin B.

As a superantigen, staphylococcal enterotoxin B (SEB) possesses the ability to bind to major histocompatibility complex class II molecules and be recognized by T cells bearing certain T-cell receptor (TCR) V beta alleles. Other investigators have utilized site-specific mutagenesis to generate amino acid substitutions to identify residues that may be involved in the interaction with the TCR beta-chain. In an attempt further to define the face of the SEB molecule involved in the interaction with the beta-chain, we have employed a polymerase chain reaction (PCR)-based, site-specific mutagenesis method to generate amino acid substitutions with altered superantigen activity. Our results show that valine at position 169 appears to be involved in the function of this superantigen, since each of several substitutions at this position exhibit a significantly reduced ability to induce T-cell proliferation. Analysis of the responding T cells to the residue 169 substitution shows that the mutant toxins maintain TCR V beta selectivity. At the same time, mutation of the proximal histidine at position 166 does not alter the superantigen activity of SEB. Radiolabelled binding analysis of these H166 and V169 mutants shows that class II-binding activity is not significantly altered. When viewed in the context of other results reported in the literature, combined with the crystal structure of the toxin, our results suggest that the interaction with the TCR probably involves SEB residues which ring a cavity along one side of the toxin molecule.

Animals↗