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Biomedical subjects

G Wang

Publications and source records attributed to G Wang.

At least 721 records · Page 40Linked to original sources
PubMed1994

The structure of a neutralized virus: canine parvovirus complexed with neutralizing antibody fragment.

BACKGROUND: Members of the Parvovirus genus cause a variety of diseases in mammals, including humans. One of the major defences against viral infection is the presence of neutralizing antibodies that prevent virus particles from infecting target cells. The mechanism of neutralization is not well understood. We therefore studied the structure of canine parvovirus (CPV) complexed with the Fab fragment of a neutralizing antibody, A3B10, using image reconstruction of electron micrographs of vitrified samples, together with the already known structure of CPV from X-ray crystallographic data. RESULTS: The structure of the complex of CPV with Fab A3B10 has been determined to 23 A resolution. The known CPV atomic structure was subtracted from the electron density of the complex, and the difference map was used to fit the atomic coordinates of a known Fab fragment, HyHEL-5. The long axis of each Fab molecule is oriented in a near radial direction, inclined away from the two-fold axes. The viral epitope consists of 14 amino acid residues found in loops 1, 2 and 3 on the capsid surface, which include previously identified escape mutations. CONCLUSIONS: The mode of Fab binding suggests that the A3B10 neutralizing antibody cannot bind bivalently to the capsid across the two-fold axes, consistent with the observation that whole A3B10 antibody readily precipitates CPV. Since Fab A3B10 can also neutralize the virus, mechanisms of neutralization such as interference with cell attachment, cell entry, or uncoating, must be operative.

Amino Acid Sequence↗
PubMed1994

Specificity of vascular endothelial cell growth factor receptor ligand binding domains.

Vascular endothelial cell growth factor binds with high affinity to FLT and KDR, two homologous tyrosine kinase receptors expressed on vascular endothelial cells. Placental growth factor, a vascular endothelial cell growth factor homologue, also binds with high affinity to the extracellular domains of FLT but not to the extracellular region of KDR. Vascular endothelial cell growth factor binds competitively with placental growth factor to the extracellular ligand binding domains of FLT, indicating that both ligands probably complex to overlapping or identical regions of this receptor.

Binding Sites↗
PubMed1994

Mycoplasma gallisepticum strain differentiation by arbitrary primer PCR (RAPD) fingerprinting.

We demonstrate here that the arbitrary primer polymerase-chain-reaction-based DNA fingerprinting method (also termed random amplified polymorphic DNA or RAPD) can be used to distinguish among strains of the avian pathogen Mycoplasma gallisepticum. Ten base oligonucleotide primers were used individually to prime DNA synthesis from genomic DNAs. Strain-specific arrays of DNA fragments were generated, which allowed us to identify and group isolates. Isolates of M. synoviae, M. gallinarum and M. iners yielded arrays of DNA fragments that differed markedly from those generated from the M. gallisepticum isolates using the same arbitrary primers. These results show that the RAPD fingerprinting method distinguishes genetically different strains of M. gallisepticum and indicates that it should be valuable for monitoring transmission of this pathogen.

Animals↗
PubMed1994

Blood acetone concentration in "normal people" and in exposed workers 16 h after the end of the workshift.

Acetone levels were measured by gas chromatography mass spectrometry (GC-MS) in environmental and alveolar air, blood and urine of 89 non-occupationally exposed subjects and in three groups of workers exposed to acetone or isopropanol. Acetone was detected in all samples from non-exposed subjects, with mean values of 840 micrograms/l in blood (Cb), 842 micrograms/l in urine (Cu), 715 mg/l in alveolar air (Ca) and 154 ng/l in environmental air (Ci). The ninety-fifty percentiles were 2069 micrograms/l in Cb, 2206 micrograms/l in Cu and 1675 ng/l in Ca. The blood/air partition coefficient of acetone was 597. Correlations were found in Cb, Cu and Ca. In specimens sampled at the end of the workshift from subjects occupationally exposed to acetone, a correlation was found in the blood, urine, alveolar and environmental air concentrations. The blood/air partition coefficient of acetone was 146. On average, the blood acetone levels of workers were 56 times higher than the environmental exposure level, and the concentration of acetone in alveolar air was 27% more than that found in inspiratory air. The half-life for acetone in blood was 5.8 h in the interval of 16 h between the end of the workshift and the morning after. The morning after a workshift with a mean acetone exposure of 336 micrograms/l, blood and urinary levels were 3.5 mg/l and 13 mg/l, respectively, which were still higher than those found in "normal" subjects. It can be concluded that endogenous production of acetone and environmental exposure to acetone or isopropanol do not affect the reliability of biological monitoring of exposed workers, even 16 h after low exposure.

Acetone↗
PubMed1994

In vitro investigations of the effects of nonfreezing low temperatures on lesioned and uninjured mammalian spinal neurons.

This two-part investigation explored the parameters and mechanisms of: (1) injury to spinal cord (SC) neurons by nonfreezing low temperatures, and (2) hypothermic protection of SC neurons subjected to a defined, physical injury (dendrite transection). Conclusions from the studies of hypothermic injury were: (1) morphologic and ultrastructural signs of stress developed in SC neurons as the temperature was decreased below 17 degrees C; (2) most neurons showing stress during cooling died upon rewarming to 37 degrees C; (3) spontaneous SC network activity was not significantly changed by cooling to 17 degrees C for 2 hours and rewarming, but cooling to 10 degrees C for 1 hour caused a reduction of burst frequency after rewarming, and cooling to 10 degrees C for 2 hours resulted in electrical silence after rewarming; and (4) application of N-methyl-D-aspartate (NMDA) antagonists before cooling prevented neuronal death, ultrastructural damage, and loss of activity upon rewarming, but application after cooling (before rewarming) was not protective. Conclusions from the studies of hypothermic protection were: (1) cooling at 17 degrees C for 2 hours followed by rewarming to 37 degrees C significantly increased lesioned neuron survival, but protection was lost when the period at 17 degrees C was increased to 6 hours; (2) NMDA blockade under normothermic (37 degrees C) or hypothermic (17 degrees C or 10 degrees C for 2 hours) conditions was not more protective of lesioned neurons than cooling to 17 degrees C (no NMDA antagonist); and (3) 200 microM thiopental or 100 microM pentobarbital increased lesioned neuron survival to a degree comparable to cooling for 2 hours at 17 degrees C.

Cell Death↗
PubMed1994

Spatial variation of section sensitivity profile in spiral computed tomography.

The section sensitivity profile (SSP) is widely used to describe the longitudinal image resolution in computed tomography (CT). Due to asymmetry in spiral CT interpolation, the SSP depends on the transverse position of the associated longitudinal line. Spatial variation in the spiral CT SSP has not been investigated previously. To determine the SSP variation over the scan field, the SSP for the half-scan interpolation method in terms of its transverse position was formulated. Based on the SSP formula, mathematical analysis and numerical simulation were performed. It was shown that the SSP associated with a transverse slice is antisymmetric with respect to the abscissa axis (which connects the slice center and the source location in the slice). Moment analysis was conducted on the SSP up to order three. The area under the SSP is equal to that under the longitudinal detector response function. As a result, with a normalized SSP the total mass of an object approximately remains after reconstruction. The mean of the SSP is equal to zero, although the SSP is asymmetric. The standard deviation and skewness of the SSP were numerically simulated and plotted for typical imaging parameters. It was demonstrated that for a 50 degrees fan angle (which is extended by two extreme rays in a fan beam) the relative change in the slice thickness is no more than 10%, while the skewness of the SSP is within about 0.15. The smaller the fan angle, the less the SSP spatial variation. Therefore, in spiral CT the SSP along the longitudinal axis can be used as a representative of the SSP family.

Humans↗
PubMed1994

Longitudinal resolution in volumetric x-ray computerized tomography--analytical comparison between conventional and helical computerized tomography.

The primary advantage of helical computerized tomography (CT) is the capability of scanning a complete anatomical volume in a single breath hold. Due to the table motion and subsequent interpolation process, the slice sensitivity profile (SSP) in helical CT is worse than the response function of the detector array. In this paper, image longitudinal resolution in volumetric x-ray CT is analytically characterized, and a comparison made between conventional and helical CT. First, the SSPs are derived for both conventional and helical CT with the half-scan interpolation method under the condition that the table increment and detector collimation are the same. Then, the corresponding transfer functions are obtained for bandwidth determination, which directly describe the spatial resolution. Both one-tenth-cutoff and mean-square-root measures are used to quantify the bandwidth. Although it appears that broadening the SSP in helical CT could adversely affect longitudinal resolution, it is proved that for a given x-ray dose, helical CT allows substantially better longitudinal resolution than conventional CT due to its inherent retrospective reconstruction capability. To make full use of the potential of helical CT scan data, it is recommended that about five slices be reconstructed per table increment. Helical CT is superior in applications requiring a high longitudinal resolution.

Algorithms↗
PubMed1994

Inversions and deletions generated by a mini-gamma delta (Tn1000) transposon.

Intramolecular transposition by an engineered derivative of the transposon gamma delta (Tn1000) is described. This 1-kb element contains inverted repeats of the 40 bp of the delta end of gamma delta, bracketing a kan gene, but it contains no resolution site. Transposition was analyzed in two plasmids; one contained two contraselectable (conditional lethal) genes (thyA and sacB) adjacent to the mini-gamma delta element in a 13.0-kb pBR322/pUC-based two-component plasmid (a heterodimer), and the other contained a different contraselectable gene (strA [rpsL]) in a 13.2-kb three-component plasmid (a heterotrimer). Selection for loss of function of a single contraselectable gene yielded inversions and deletions. Each inversion plasmid was 1 kb larger than the parent plasmid: it had a second copy of mini-gamma delta inserted in the contraselected gene, with that copy plus the intervening segment inverted, and the 5-bp target site duplicated. Each deletion plasmid was smaller than the parent plasmid and had a deletion that extended from one transposon end into or through the contraselected gene for distances of up to 9.4 kb. The frequencies of deletions versus inversions ending in a single target gene were similar, although overall, deletions outnumbered inversions because deletions, but not inversions, into sites beyond the contraselected gene inactivate it. This work also demonstrates that thyA (which encodes thymidylate synthetase) is a useful contraselectable marker.

Base Sequence↗
PubMed1994

Helical CT: principles and technical considerations.

The performance of helical CT requires several user-defined parameters that exceed the requirements of conventional CT. One needs to carefully select the collimation, table increment, and reconstruction interval. Minimizing these parameters maximizes longitudinal resolution but with various trade-offs. Decreasing the collimation decreases the effective section thickness but increases pixel noise. Limiting the table increment to a pitch of 1 limits the broadening of the effective section thickness associated with the helical technique but also limits the coverage that can be achieved with a given helical scan. Our general practice is to minimize the collimation to cover the volume of interest and to accept a pitch up to 2, provided that we are using 180 degree interpolation. The reconstruction interval is also minimized to maximize longitudinal resolution but with trade-offs of increased image processing time, data storage requirements, and physician time for image review. For routine diagnosis, we recommend reconstruction of one to two sections per table increment, and, for multiplanar and three-dimensional imaging, we recommend at least three sections be reconstructed per table increment. The scan duration is dictated by both patient and machine factors.

Artifacts↗