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Biomedical subjects

X Fan

Publications and source records attributed to X Fan.

At least 73 records · Page 4Linked to original sources
PubMed2000

Prolongation of liver allograft survival after interleukin-10 gene transduction 24-48 hours before donation.

BACKGROUND: Interleukin- (IL) 10 may be a potent regulator for controlling of allograft rejection. A single administration of IL-10 is not effective for controlling graft rejection. Gene transfer is an attractive vehicle for prolonging the expression of short-lived proteins. METHODS: Donor or recipient livers were transduced with 1 x 10(10) p.f.u. of replication-deficient adenovirus vectors harboring human IL-10 cDNA (AdCMVhIL-10) via the ileocecal vein before or after rat orthotopic liver transplantation. RESULTS: DA allografts given AdCMVhIL-10 24-48 hr before donation survived for more than 56 days in Lewis recipients, although DA allografts given the adenovirus vector 7 days or 6 hr before, and 3 days after transplantation were rejected within 30 days in recipients. Serum levels of human IL-10 in gene-transferred rats were maximum from day 2 to 7. The serum level of human IL-10 then decreased gradually, and human IL-10 was not detected by ELISA 30 days after gene-transduction. In gene-transduced long-term surviving liver allografts, IL-10 was expressed, and the expression of IL-4 was also up-regulated on posttransplant day 3, despite the expression of Th1 cytokines (IL-2 and interferon-gamma), although in rejected liver allografts, IL-2 and interferon-gamma were expressed without expression of IL-4 and IL-10. CONCLUSIONS: The prolongation of survival of IL-10 cDNA transferred liver allografts might be due to inhibition of the early phase of alloimmune-response by over expression of IL-10, despite the expression of IL-2 and interferon-gamma.

Animals↗
PubMed2000

The Missing Link: Early Methane ("T") Dwarfs in the Sloan Digital Sky Survey.

We report the discovery of three cool brown dwarfs that fall in the effective temperature gap between the latest L dwarfs currently known, with no methane absorption bands in the 1-2.5 µm range, and the previously known methane (T) dwarfs, whose spectra are dominated by methane and water. The newly discovered objects were detected as very red objects in the Sloan Digital Sky Survey imaging data and have JHK colors between the red L dwarfs and the blue Gl 229B-like T dwarfs. They show both CO and CH(4) absorption in their near-infrared spectra in addition to H(2)O, with weaker CH(4) absorption features in the H and K bands than those in all other methane dwarfs reported to date. Due to the presence of CH(4) in these bands, we propose that these objects are early T dwarfs. The three form part of the brown dwarf spectral sequence and fill in the large gap in the overall spectral sequence from the hottest main-sequence stars to the coolest methane dwarfs currently known.

Journal Article↗
PubMed2000

Efficient adenoviral vector transduction of human hematopoietic SCID-repopulating and long-term culture-initiating cells.

This article presents our studies on the adenoviral transduction efficiency, level of transgene expression, cell cycle status, and multilineage reconstitution ability of human CD34+ hematopoietic cells transduced under proliferating and survival growth conditions. Bone marrow and umbilical cord blood CD34+ cells were cultured in serum-free medium under survival conditions with thrombopoietin (Tpo) alone, or under proliferating conditions with Tpo, c-Kit ligand (KL), and Flt3 ligand (FL). Adenoviral vectors carrying the enhanced green fluorescent protein (EGFP) gene under the control of the PGK-1 promoter were used to transduce CD34+ cells. Approximately 10% of CD34+ cells were EGFP+ under both culture conditions. In contrast, up to 50% of CD34+CD38- cells were EGFP+, whereas a maximum of 8% of CD34+CD38(high) cells were EGFP+ (p < 0.001). Both colony-forming unit cells (CFU-C) and 5-week long-term culture-initiating cells (LTC-ICs) were efficiently transduced. Under survival conditions, a substantial fraction of transduced CD34+ cells remained quiescent. The nondividing CD34+EGFP+ cells contained LTC-ICs capable of reconstituting longterm culture for as long as 10 weeks. CD34+EGFP+ cells also retained the ability to engraft and multilineage-reconstitute NOD/SCID mice. These observations demonstrate that primitive human hematopoietic progenitor cells can be efficiently transduced by adenoviral vectors.

ADP-ribosyl Cyclase↗
PubMed2000

Atomic arrangement of iodine atoms inside single-walled carbon nanotubes

We report atomic resolution Z-contrast scanning transmission electron microscopy images that reveal the incorporation of I atoms in the form of helical chains inside single-walled carbon nanotubes. Density functional calculations and topological considerations provide a consistent interpretation of the experimental data. Charge transfer between the nanotube walls and the I chains is associated with the intercalation.

Journal Article↗
PubMed2000

Dust Emission from High-Redshift QSOs.

We present detections of emission at 250 GHz (1.2 mm) from two high-redshift QSOs from the Sloan Digital Sky Survey sample using the bolometer array at the IRAM 30 m telescope. The sources are SDSSp 015048.83+004126.2 at z=3.7 and SDSSp J033829.31+002156.3 at z=5.0; the latter is the third highest redshift QSO known and the highest redshift millimeter-emitting source yet identified. We also present deep radio continuum imaging of these two sources at 1.4 GHz using the Very Large Array. The combination of centimeter and millimeter observations indicate that the 250 GHz emission is most likely thermal dust emission, with implied dust masses approximately 108 M middle dot in circle. We consider possible dust heating mechanisms, including UV emission from the active galactic nucleus (AGN) and a massive starburst concurrent with the AGN, with implied star formation rates greater than 103 M middle dot in circle yr-1.

Journal Article↗
PubMed2000

The Discovery of a Second Field Methane Brown Dwarf from Sloan Digital Sky Survey Commissioning Data.

We report the discovery of a second field methane brown dwarf from the commissioning data of the Sloan Digital Sky Survey (SDSS). The object, SDSS J134646.45-003150.4 (hereafter SDSS 1346-00), was selected because of its very red color and stellar appearance. Its spectrum between 0.8 and 2.5 µm is dominated by strong absorption bands of H2O and CH4 and closely mimics those of Gliese 229B and SDSS 162414.37+002915.6 (hereafter SDSS 1624+00), two other known methane brown dwarfs. SDSS 1346-00 is approximately 1.5 mag fainter than Gliese 229B, suggesting that it lies about 11 pc from the Sun. The ratio of flux at 2.1 µm to that at 1.27 µm is larger for SDSS 1346-00 than for Gliese 229B and SDSS 1624+00, which suggests that SDSS 1346-00 has a slightly higher effective temperature than the others. Based on a search area of 130 deg2 and a detection limit of z*=19.8, we estimate a space density of 0.05 pc-3 for methane brown dwarfs with Teff approximately 1000 K in the 40 pc3 volume of our search. This estimate is based on small-sample statistics and should be treated with appropriate caution.

Journal Article↗
PubMed2000

Transcriptional regulation of the expression of macrophage colony stimulating factor.

The regulatory regions for transcriptional control of the MCSF gene are unknown. We examined regulatory control in a 774-bp murine MCSF promoter transfected into MC3T3-E1 osteoblast-like and COS-7 cells. Deletion of upstream sequence from -635 increased basal activity of the promoter by at least four-fold, an increase that was maintained when PU.1, NFkappaB and Egr1/Sp1 consensus sequences were subsequently removed. Mutagenesis identified a suppressor element between -635 and -642 from the transcriptional start site and an oligonucleotide representing this sequence was retarded by nuclear cell protein. TNFalpha (1 ng/ml), PTH (5x10(-8) M), and IL-1alpha (100 pg/ml), which increased MCSF protein secretion, failed to enhance the transcriptional rate of the full-length promoter. TNFalpha was able to stimulate transcription of a heterologous reporter transfected into COS-7 containing multiple copies of the murine MCSF NFkappaB site inserted before a minimal promoter. In contrast, deletion of the same NFkappaB response element increased basal activity in the native promoter. Thus, the NFkappaB sequence may act as a negative regulator in the context of the endogenous promoter. Our results indicate that constitutive transcriptional activity conferred by the MCSF promoter may be damped by a suppressor protein. Transcriptional regulation, however, does not appear to be a major stimulatory mechanism for MCSF secretion.

3T3 Cells↗
PubMed2000

Uptake of a superparamagnetic contrast agent imaged by MR with high spectral and spatial resolution.

Conventional MRI implicitly treats the proton signal as a single, narrow Lorentzian. However, water signals in vivo are often in homogeneously broadened and have multiple resolvable components. These components represent discrete populations of water molecules within each pixel which are affected differently by physiology and contrast agents. Accurate measurement of each component of the water resonance can improve anatomic and functional MR images and provide insight into the structure and dynamics of subpixelar microenvironments. This report describes high spectral and spatial resolution (HiSS) MR imaging of rodent prostate tumors before and after injection of a superparamagnetic contrast agent. HiSS datasets were used to synthesize images in which intensity is proportional to peak height, peak frequency, and linewidth. These images showed anatomic features which were not clearly delineated in conventional T(2) and gradient echo images. HiSS images obtained after injection of the contrast agent showed T *(2) and T(1) changes which were not seen in conventional images. These changes are associated with microvessel density and permeability. The results suggest HiSS with superparamagnetic contrast agents has the potential to improve characterization of tumors.

Animals↗
PubMed2000

RALDH3, a retinaldehyde dehydrogenase that generates retinoic acid, is expressed in the ventral retina, otic vesicle and olfactory pit during mouse development.

The enzymes that generate retinoic acid during development have been identified as members of the aldehyde dehydrogenase (ALDH) family. The developmental expression patterns of two ALDHs that function as retinaldehyde dehydrogenases, RALDH1 and RALDH2, have been described. Here we report the cloning and expression of a third retinaldehyde dehydrogenase from the mouse called RALDH3 that shares 94% amino acid sequence identity to a human retinaldehyde dehydrogenase previously named ALDH6. In mouse embryos, RALDH3 expression is first noticed in the ventral optic eminence at E8.75, then in the optic vesicle/cup, otic vesicle, and olfactory placode/pit from E9.5 to E11.5. Expression in the developing eye is primarily localized in the ventral retina, thus indicating that RALDH3 represents the V1 dehydrogenase activity described there earlier. From E8.5 to E10.5 RALDH3 expression is distinct from that of RALDH1 or RALDH2, thus indicating a unique role in sensory organ development.

Aldehyde Oxidoreductases↗
PubMed2000

Adenoviral vector design for high-level transgene expression in primitive human hematopoietic progenitors.

Adenoviral vector-mediated transient gene expression can provide new possibilities for ex vivo manipulation of quiescent hematopoietic stem cells (HSC). In order to define a suitable expression cassette for high levels of transgene expression in HSCs, we have studied the level of transgene expression in human CD34+CD38- cells using adenoviral vectors with various gene expression cassettes encoding the enhanced green fluorescence protein (EGFP) gene. CD34+ hematopoietic cells were cultured in serum-free medium with megakaryocyte growth and development factor (MGDF) alone for supporting the survival of primitive progenitors or with MGDF, c-kit ligand (KL) and flt3 ligand (FL) for inducing proliferation of primitive progenitors. With all the vectors tested, higher percentages of EGFP expressing cells were found in CD34+CD38- cells than those in CD34+CD38high cells from all donors tested. The phosphoglycerate kinase (PGK)-1 promoter was found to allow higher levels of EGFP expression than the human cytomegalovirus (HCMV) promoter in CD34+CD38- cells. Replacing the SV40 polyadenylation signal with the human beta-globin gene IVS2 and polyadenylation signal in the expression cassette (Ad5xPGK-EGFP-beta-globin) enhanced the level of EGFP expression markedly further. These results provide a guideline for the development of adenoviral vectors for gene expression in human primitive hematopoietic progenitor cells. Gene Therapy (2000) 7, 2132-2138.

ADP-ribosyl Cyclase↗
PubMed2000

Adopted adolescents' overrepresentation in mental health counseling: adoptees' problems or parents' lower threshold for referral?

UNLABELLED: A larger proportion of adopted adolescents receive mental health counseling than do their nonadopted peers. Adoptees might have more problems that require counseling, or their adoptive parents might have a lower threshold for referral (or both). OBJECTIVE: To test the hypothesis that both the extent of adolescents' problems and their adoption status would predict whether adolescents received psychological counseling, after controlling for family demographic characteristics. METHOD: Two large data sets collected from 1994 through 1996 by the National Longitudinal Study of Adolescent Health (Add Health) were used. In parallel analyses of the 2 data sets, hierarchical logistic regression models were implemented to assess the incremental effects of problem behaviors, family characteristics, and adoption status on adolescents receiving counseling. RESULTS: Selected adolescents' problems and family demographic characteristics were significant predictors for having received counseling, but, after controlling for these variables, adoptees were still about twice as likely as nonadoptees to have received counseling. CONCLUSIONS: Prevalence of problems, adoptive family characteristics, and adoption status must all be taken into account to understand why adoptees are more likely to receive counseling. Clinicians should be sensitive to issues that are especially salient in adoptive families.

Adolescent↗
PubMed2000

Ultrasound field estimation method using a secondary source-array numerically constructed from a limited number of pressure measurements

A new and faster method for the accurate estimation of acoustic fields of underwater ultrasonic transducers was developed, tested experimentally, and compared to previously reported methods. Using a limited number of pressure measurements close to the transducer's face, the method numerically constructs a virtual secondary source-array whose acoustic field is similar to the field generated by the actual transducer (primary source). The measured data are used to obtain the normal particle velocity on the surface of the virtual secondary source-array, which in turn permits the calculation of the forward propagating field using the Rayleigh-Sommerfeld diffraction integral. The method is novel in that it constructs a virtual secondary source-array, thus eliminating the problems associated with obtaining the excitation source of a real transducer; and it is faster because it uses finite differences instead of a matrix inversion to obtain the excitation source. Results showed that predicted ultrasound fields agreed quantitatively and qualitatively with measured fields for three commonly used transducer types: two planar radiators (one circular, 0.5 MHz, 1.9-cm diam.; and one square, 1 MHz, 1.2 cm on a side), and a sharply focused radiator (1.5 MHz, 10-cm diam., 10-cm radius of curvature). The agreements suggest that the secondary source-array method (SSAM) is applicable to a wide range of radiator sizes, shapes, and operating frequencies. The SSAM was also compared to these authors' previous equivalent phased array methods (EPAM) [J. Acoust. Soc. Am. 102, 2734-2741 (1997); and Concentric ring equivalent phased array method (CREPAM), UFFC 46, 830-841 (1999)] which require matrix inversions. The SSAM proved to be much faster and equally or more nearly accurate than the previous methods.

Journal Article↗
PubMed2000

Helicobacter pylori modulates lymphoepithelial cell interactions leading to epithelial cell damage through Fas/Fas ligand interactions.

Helicobacter pylori causes a common chronic infection of humans that leads to epithelial cell damage. Studies have shown that apoptosis of the gastric epithelium is increased during infection and this response is associated with an expansion of gastric T-helper type 1 (Th1) cells. We report that gastric T cells contribute to apoptosis of the epithelium by a Fas/Fas ligand (FasL) interaction. Fas receptor expression was detected on freshly isolated gastric epithelial cells by flow cytometry and immunohistochemistry, and this level of expression was increased during infection with H. pylori. The expression of Fas receptor on three gastric epithelial cell lines was increased by H. pylori, either alone or in combination with gamma interferon or tumor necrosis factor alpha. The role of Fas in apoptosis of gastric epithelial cell lines was evidenced by DNA fragmentation after cross-linking of Fas with specific antibodies. FasL expression was detected by immunohistochemistry on mononuclear cells in gastric biopsy specimens of infected but not uninfected subjects. Gastric T-cell lines were also shown to express FasL, as evidenced by reverse transcription-PCR and killing of target cells expressing Fas receptor. Moreover, these T-cell lines were capable of killing cultured gastric epithelial target cells and antibodies that block the interaction between Fas receptor and FasL inhibited this cytotoxic activity. These observations demonstrate that local Th1 cells may contribute to the pathogenesis of gastric disease during H. pylori infection by increasing the expression of Fas on gastric epithelial cells and inducing apoptosis through Fas/FasL interactions.

Adult↗
PubMed2000

Adaptive immunity against Listeria monocytogenes in the absence of type I tumor necrosis factor receptor p55.

Tumor necrosis factor (TNF) and the type I TNF receptor (TNFRI), p55, are critical for resistance against primary infections with the intracellular bacterial pathogen Listeria monocytogenes. Importantly, however, susceptibility to primary listeriosis in cytokine-deficient mice does not preclude the development or expression of effective adaptive immunity against virulent L. monocytogenes. We used TNFRI(-/-) mice to study adaptive antilisterial immunity in the absence of interactions between TNF and TNFRI. Our experiments indicate that TNFRI(-/-) mice survive and clear high-dose challenges with an attenuated strain of L. monocytogenes that is incapable of cell-to-cell spread. Furthermore, TNFRI(-/-) mice immunized with attenuated L. monocytogenes go on to develop potent adaptive immunity to subsequent high-dose challenges with virulent L. monocytogenes. Interestingly, CD8(+) T-cell depletion in vivo inhibits immunity to L. monocytogenes in the spleen but not in the liver of TNFRI(-/-) mice. The adaptive immune response in these animals is characterized by activation of listeriolysin O-specific CD8(+) T cells, which are capable of transferring antilisterial immunity to naive wild-type C57BL/6 host mice. These experiments demonstrate the development and expression of potent CD8(+) T-cell-mediated antilisterial immunity in the absence of TNFRI.

Adaptation, Biological↗
PubMed2000

Mechanical strain inhibits expression of osteoclast differentiation factor by murine stromal cells.

Normal dynamic loading prevents bone resorption; however, the means whereby biophysical factors reduce osteoclast activity are not understood. We show here that mechanical strain (2% at 10 cycles per minute) applied to murine marrow cultures reduced 1, 25(OH)(2)D(3)-stimulated osteoclast formation by 50%. This was preceded by decreased expression of osteoclast differentiation factor (ODF/TRANCE). RT-PCR for ODF/TRANCE revealed that ODF/TRANCE mRNA in strained cultures was 59 +/- 3% of that seen in control cultures. No significant effects on total cell count, thymidine uptake, or alkaline phosphatase activity were induced by strain. To isolate the cell targeted by strain, primary stromal cells were cultured from marrow. Mechanical strain also reduced mRNA for ODF/TRANCE to 60% that of control in these cells. In contrast, mRNA for membrane-bound macrophage colony-stimulating factor was not significantly affected. Soluble ODF ( approximately 2 ng/ml) was able to reverse the effect of strain, returning osteoclast numbers to control. Because osteoclast formation is dependent upon ODF/TRANCE expression, strain-induced reductions in this factor may contribute to the accompanying reduction in osteoclastogenesis.

Alkaline Phosphatase↗
PubMed2000

Molecular cloning and chimerisation of CDI 315B monoclonal antibody.

A chimeric mouse-human antibody has been created that recognizes an antigen found on breast cancer cells and melanoma cells. Immunoglobulin constant domains of mouse monoclonal antibody CDI 315B Cgamma1 and CK, were substituted by the human Cgamma1 and Ckappa. The CDI 315B variable heavy and light chain regions were PCR amplified from hybridoma RNA and sequenced. Mouse variable VH and VL regions were joint to human IgG1 and kappa constant regions and subcloned into pcDNA3 expression vectors. The Sp2/0 murine myeloma cells were transfected with expression vectors pcDNA3L and pcDNA3H and the reactivity of chimeric antibodies was tested by indirect ELISA using B16F1 murine melanoma cells as well as MCF7 human breast cancer cells, as antigen.

Amino Acid Sequence↗