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Biomedical subjects

J Ma

Publications and source records attributed to J Ma.

At least 37 records · Page 2Linked to original sources
PubMed2005

Highly pathogenic H5N1 influenza virus infection in migratory birds.

H5N1 avian influenza virus (AIV) has emerged as a pathogenic entity for a variety of species, including humans, in recent years. Here we report an outbreak among migratory birds on Lake Qinghaihu, China, in May and June 2005, in which more than a thousand birds were affected. Pancreatic necrosis and abnormal neurological symptoms were the major clinical features. Sequencing of the complete genomes of four H5N1 AIV strains revealed them to be reassortants related to a peregrine falcon isolate from Hong Kong and to have known highly pathogenic characteristics. Experimental animal infections reproduced typical highly pathogenic AIV infection symptoms and pathology.

Amino Acid Sequence↗
PubMed2005

Square, hexagonal, and row phases of PTCDA and PTCDI on Ag-Si(111)square root(3) x square root(3)R30 degrees.

We have investigated the ordered phases of the perylene derivatives perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA) and the imide analogue PTCDI on the Ag-Si(111)square root(3) x square root(3)R30 degrees surface using scanning tunneling microscopy. We find that PTCDA forms square, hexagonal, and herringbone phases, which coexist on the surface. The existence of a square phase on a hexagonal surface is of particular interest and is a result of a near commensurability between the molecular dimensions and the surface lattice. Contrast variations across the square islands arise from PTCDA molecules binding to different sites on the surface. PTCDI on Ag-Si(111)square root(3) x square root(3)R30 degrees forms extended rows, as well as two-dimensional islands, both of which are stabilized by hydrogen bonding mediated by the presence of imide groups. We present models for the molecular arrangements in all these phases and highlight the role of hydrogen bonding in controlling this order.

Journal Article↗
PubMed2005

The genome of the social amoeba Dictyostelium discoideum.

The social amoebae are exceptional in their ability to alternate between unicellular and multicellular forms. Here we describe the genome of the best-studied member of this group, Dictyostelium discoideum. The gene-dense chromosomes of this organism encode approximately 12,500 predicted proteins, a high proportion of which have long, repetitive amino acid tracts. There are many genes for polyketide synthases and ABC transporters, suggesting an extensive secondary metabolism for producing and exporting small molecules. The genome is rich in complex repeats, one class of which is clustered and may serve as centromeres. Partial copies of the extrachromosomal ribosomal DNA (rDNA) element are found at the ends of each chromosome, suggesting a novel telomere structure and the use of a common mechanism to maintain both the rDNA and chromosomal termini. A proteome-based phylogeny shows that the amoebozoa diverged from the animal-fungal lineage after the plant-animal split, but Dictyostelium seems to have retained more of the diversity of the ancestral genome than have plants, animals or fungi.

ATP-Binding Cassette Transporters↗
PubMed2005

Temporal and spatial variabilities of atmospheric polychlorinated biphenyls (PCBs), organochlorine (OC) pesticides and polycyclic aromatic hydrocarbons (PAHs) in the Canadian Arctic: results from a decade of monitoring.

The Northern Contaminants Program (NCP) baseline monitoring project was established in 1992 to monitor for persistent organic pollutants (POPs) in Arctic air. Under this project, weekly samples of air were collected at four Canadian and two Russian arctic sites, namely Alert, Nunavut; Tagish, Yukon; Little Fox Lake, Yukon; Kinngait, Nunavut; Dunai Island, Russia and Amderma, Russia. Selected POPs, including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine (OC) pesticides, were analyzed in both the gas and particulate phases. This paper summarizes results obtained from this project in the past 5 years. Temporal trends were developed for atmospheric PCBs and OCs observed at Alert using a digital filtration (DF) technique. It was found that trends developed with 5 years of data (1993-1997) did not differ significantly from those determined with 7 years of data (1993-1999). This implies that with the DF technique, long-term trends can still be developed with less than 10 years of data. An acceleration in decline of OC and PCB air concentrations was noted in 1999 for some compounds, although the reason is unknown. Monitoring efforts must continue to assess the effect of this decline on the long-term trends of POPs in the Canadian Arctic. Occasional high trans-/cis-chlordane ratios and heptachlor air concentrations measured at Alert between 1995 and 1997 suggests sporadic fresh usage of chlordane-based pesticides. However, significant decreasing trends of chlordanes along with their chemical signatures has provided evidence that emission of old soil residues is replacing new usage as an important source to the atmosphere. Measurements of OC air concentrations conducted at Kinngait in 1994-1995 and 2000-2001 indicated faster OC removal at this location than at Alert. This may be attributed to the proximity of Kinngait to temperate regions where both biotic and abiotic degradation rates are faster. The PAH concentrations observed at Alert mimic those at mid-latitudes and are consistent with long-range transport to the Arctic, particularly for the lighter PAHs. A decline in particulate PAH was observed, similar to atmospheric sulphate aerosol and can be attributed to the collapse of industrial activity in the former Soviet Union between 1991 and 1995. Spatial comparisons of OC seasonality at Alert, Tagish, Dunai and Kinngait show elevated air concentrations of some compounds in spring. However, elevated spring concentrations were observed for different compounds at different sites. Potential causes are discussed. Further investigation in the atmospheric flow pattern in spring which is responsible for the transport of POPs into the Arctic is required. OC and PCB air concentrations at Alert were found to be influenced by two climate variation patterns, the North Atlantic Oscillation (NAO) and the Pacific North American (PNA) pattern. Planetary atmospheric patterns must be taken into account in the global prediction and modelling of POPs in the future.

Journal Article↗
PubMed2005

Constitutive modeling of the densification and the grain growth of hydroxyapatite ceramics.

In the present work, constitutive models for densification and grain growth were employed to investigate the sintering behavior of pure hydroxyapatite ceramics. For densification study, lattice diffusion, grain-boundary diffusion, and interface reaction mechanisms, and for grain-growth study, surface diffusion mechanism, were considered respectively. Hydroxyapatite ceramics were pressurelessly sintered. The sintering results were discussed and compared with the modeling results. Based on the constitutive models employed and the experimental results obtained, grain-boundary diffusion was identified as the dominant mechanism for the densification of the investigated hydroxyapatite. The grain-growth model provided a good prediction to the grain growth of the investigated hydroxyapatite. The activation energies for densification and grain growth of hydroxyapatite ceramics were evaluated as 1150+/-40 and 1020+/-40 KJ mol(-1), respectively.

Biocompatible Materials↗
PubMed2005

AFM study of hippocampal cells cultured on silicon wafers with nano-scale surface topograph.

The rat hippocampal cells were selected as model to study the interaction between the neural cells and silicon substrates using atomic force microscopy (AFM). The hippocampal cells show tight adherence on silicon wafers with nano-scale surface topograph. The lateral friction force investigated by AFM shows significant increase on the boundary around the cellular body. It is considered to relate to the cytoskeleton and cellular secretions. After ultrasonic wash in ethanol and acetone step by step, the surface of silicon wafers was observed by AFM sequentially. We have found that the culture leftovers form tight porous networks and a monolayer on the silicon wafers. It is concluded that the leftovers overspreading on the silicon substrates are the base of cell adherence on such smooth inert surfaces.

Acetone↗
PubMed2005

Interleukin-2alpha receptor in membrane lipid rafts.

Acute allograft rejection is driven by production of cytokines such as interleukin(IL)-2 that activate and expand alloreactive T cells by ligating high-affinity IL-2alpha receptors. Lipid rafts on the membranes of T cells may be the functional microdomains for IL-2alpha receptor. Flow cytometric analysis was performed for expression of CD25 (IL-2alpha receptor) on the surface of T cells. Lipid rafts were isolated by discontinuous sucrose density gradient ultracentrifugation. The localization of IL-2Ralpha in fractions isolated from sucrose density gradients was determined by immunoblotting and detected by chemiluminescence. Cells were stimulated with IL-2 and expression of CD25 (IL-2alpha receptor) on the surface of T cells was 37.08%. Immunoblot analysis of fractions from sucrose gradients revealed that a large proportion of IL-2Ralpha was localized in lipid rafts. Lipid rafts are the functional microdomains for IL-2alpha receptors.

Flow Cytometry↗
PubMed2005

A candidate gene approach to searching for low-penetrance breast and prostate cancer genes.

Most cases of breast and prostate cancer are not associated with mutations in known high-penetrance genes, indicating the involvement of multiple low-penetrance risk alleles. Studies that have attempted to identify these genes have met with limited success. The National Cancer Institute Breast and Prostate Cancer Cohort Consortium--a pooled analysis of multiple large cohort studies with a total of more than 5,000 cases of breast cancer and 8,000 cases of prostate cancer--was therefore initiated. The goal of this consortium is to characterize variations in approximately 50 genes that mediate two pathways that are associated with these cancers--the steroid-hormone metabolism pathway and the insulin-like growth factor signalling pathway--and to associate these variations with cancer risk.

Breast Neoplasms↗
PubMed2005

A novel approach to remove nitrogen in a biological aerobic filter (BAF).

Laboratory study on nitrogen removal was carried out using biological aerobic filter (BAF) fed with synthetic domestic wastewater in the temperature range of 20.5-26.5 degrees C in order to gain insight into the mechanism and the influences of operation parameters on nitrite accumulation in the biological nitrogen removal process. Influent loading with 0.26-0.62 kg (m(3)d(-1)) NH4+-N, 0.28-0.63 kg (m(3)d(-1)) TN, 1-2 m h(-1) hydraulic loading and air/ water ratio 3:1, resulted in the removal of NH4+-N and TN by 0.15-0.52 kg (m(3)d(-1)) and 0.18-0.42 kg (m(3)d(-1)) respectively. Hence BAF seems to be a promising nitrogen removal technique. The investigation of nitrite concentrations in the bulk and effluent, the profiles of inorganic nitrogen compounds and the spatial distribution of microbial populations and activity indicated that the nitrite accumulation and shortcut nitrification-denitrification had taken place in the bioreactor. No clear relationships were observed between the nitrite accumulation with the influent loading, temperature and pH value except that nitrite concentrations in the bulk increased with high back washing frequency. The results suggested that the filter structure and operation pattern were the principal factors that cause the nitrite accumulation and shortcut nitrification-denitrification occurring in the biological aerobic filter.

Bacteria↗
PubMed2004

Altered neurotrophin receptor function in the developing prefrontal cortex leads to adult-onset dopaminergic hyperresponsivity and impaired prepulse inhibition of acoustic startle.

BACKGROUND: Survival and differentiation of neurons and the formation and maintenance of synapses in the cerebral cortex may be affected in schizophrenia. Since neurotrophins play an important role in these events, behavioral effects relevant to schizophrenia were investigated in rats that had compromised neurotrophin function during prefrontal cortical development. METHODS: Neonatal rat pups were injected into the developing prefrontal cortex with a depot preparation of p75 receptor antibody conjugated to saporin. Animals were tested for dopaminergic hyperresponsivity and prepulse inhibition of acoustic startle at 5 or 10 weeks. Neonatal and adult brain sections were examined for morphologic abnormality. RESULTS: Animals that received neonatal injections of p75 antibody conjugated to saporin showed significantly increased amphetamine-induced locomotion and rearing and impairment of prepulse inhibition of acoustic startle at 10 weeks of age but not at 5 weeks. Examination of adult brain sections revealed apparently normal structure, whereas neonatal brain sections showed apoptotic cells in the developing prefrontal cortex in pups that received p75 antibody conjugated to saporin. CONCLUSIONS: Compromised p75 neurotrophin receptor function in the developing prefrontal cortex may be associated with the manifestation of adult-onset dopaminergic hyperresponsivity and impaired prepulse inhibition and therefore may be involved in the pathogenesis of schizophrenia.

Acoustic Stimulation↗
PubMed2004

Measuring membrane potential and electric field of brainstem neurons in vitro by confocal microscopy.

A method of measuring transmembrane potential and electric field of neural cells cultured in vitro is described in this paper. The high resolution and scanning speed of the method make it considerable to be used to observe the viability of the neurons cultured on opaque substrate. Rhodamine 123 was used to stain the cells in order to display different intensity corresponding to transmembrane potential. The fluorescence data were collected by confocal laser scanning microscopy (CLSM). Then the data were processed to create the graphs of transmembrane potential and electric field. This is the first paper describes a reliable method for three-dimensional visualization of potential voltage of neurons at the best of our knowledge.

Animals↗
PubMed2004

Evaluation of serotypes of Staphylococcus aureus strains used in the production of a bovine mastitis bacterin.

The five Staphylococcus aureus strains used in the manufacture of a commercially available bacterin were examined for capsular and surface polysaccharide serotypes. Double immunodiffusion assays of antigenic extracts of test and reference strains with monospecific typing sera to capsular serotypes 1, 2, 5, and 8 and to surface polysaccharide serotype 336 were performed to detect the specific reactivities and antigenic relationships of test samples. Antigenic extracts of two S. aureus strains reacted with antibodies to serotype 8, but not with antibodies to serotype 5, by producing specific precipitin lines. A third strain reacted with monospecific antibodies to serotype 5 and not with the antibodies to serotype 8. The extracts of two other strains failed to exhibit any detectable reaction with antiserum to serotypes 1, 2, 5, or 8. Antibodies to serotype 336, however, precipitated an identical, specific 336 antigen from the antigenic extracts of these two nontypeable strains. Thus, S. aureus bacterin includes one serotype 5, two serotype 8, and two serotype 336 strains, the three predominant serotypes responsible for bovine mastitis.

Animals↗
PubMed2004

Manipulating the host response to autologous tumour vaccines.

From our way of thinking the problem facing vaccine strategies for cancer is not that we do not have "enough" tumour antigens. The problem is we cannot induce an immune response that is sufficient to mediate tumour regression. The normal "checks and balances" found in the body prevent the sustained expansion and subsequent persistence of immune killer cells. If vaccine strategies are going to become effective treatments for cancer patients, they will need to overcome this substantial roadblock. Recent developments in immunology have provided insights into the mechanisms that regulate the expansion and persistence of T cells. This has allowed investigators to reinterpret decades-old observations suggesting that chemotherapy administered before vaccination often led to a stronger immune response. This manuscript will review experiments that offer an explanation for these observations and present pre-clinical data from our laboratory that describes an innovative new approach to combining chemotherapy and vaccination. This approach is readily translatable to the clinic and is broadly applicable to any vaccine strategy for advanced cancer.

Antigens, Neoplasm↗