Biomedical subjects

Zhimin Song

Publications and source records attributed to Zhimin Song.

5 recordsLinked to original sources

PubMed2006

Electronic confinement and coherence in patterned epitaxial graphene.

Ultrathin epitaxial graphite was grown on single-crystal silicon carbide by vacuum graphitization. The material can be patterned using standard nanolithography methods. The transport properties, which are closely related to those of carbon nanotubes, are dominated by the single epitaxial graphene layer at the silicon carbide interface and reveal the Dirac nature of the charge carriers. Patterned structures show quantum confinement of electrons and phase coherence lengths beyond 1 micrometer at 4 kelvin, with mobilities exceeding 2.5 square meters per volt-second. All-graphene electronically coherent devices and device architectures are envisaged.

Journal Article↗

PubMed2005

Mycobacterial catalase-peroxidase is a tissue antigen and target of the adaptive immune response in systemic sarcoidosis.

Sarcoidosis is a disease of unknown etiology characterized by noncaseating epithelioid granulomas, oligoclonal CD4(+) T cell infiltrates, and immune complex formation. To identify pathogenic antigens relevant to immune-mediated granulomatous inflammation in sarcoidosis, we used a limited proteomics approach to detect tissue antigens that were poorly soluble in neutral detergent and resistant to protease digestion, consistent with the known biochemical properties of granuloma-inducing sarcoidosis tissue extracts. Tissue antigens with these characteristics were detected with immunoglobulin (Ig)G or F(ab')(2) fragments from the sera of sarcoidosis patients in 9 of 12 (75%) sarcoidosis tissues (150-160, 80, or 60-64 kD) but only 3 of 22 (14%) control tissues (all 62-64 kD; P = 0.0006). Matrix-assisted laser desorption/ionization time of flight mass spectrometry identified Mycobacterium tuberculosis catalase-peroxidase (mKatG) as one of these tissue antigens. Protein immunoblotting using anti-mKatG monoclonal antibodies independently confirmed the presence of mKatG in 5 of 9 (55%) sarcoidosis tissues but in none of 14 control tissues (P = 0.0037). IgG antibodies to recombinant mKatG were detected in the sera of 12 of 25 (48%) sarcoidosis patients compared with 0 of 11 (0%) purified protein derivative (PPD)(-) (P = 0.0059) and 4 of 10 (40%) PPD(+) (P = 0.7233) control subjects, suggesting that remnant mycobacterial catalase-peroxidase is one target of the adaptive immune response driving granulomatous inflammation in sarcoidosis.

Antigens, Bacterial↗

PubMed2005

Liquid carbon, carbon-glass beads, and the crystallization of carbon nanotubes.

The formation of carbon nanotubes in a pure carbon arc in a helium atmosphere is found to involve liquid carbon. Electron microscopy shows a viscous liquid-like amorphous carbon layer covering the surfaces of nanotube-containing millimeter-sized columnar structures from which the cathode deposit is composed. Regularly spaced, submicrometer-sized spherical beads of amorphous carbon are often found on the nanotubes at the surfaces of these columns. Apparently, at the anode, liquid-carbon drops form, which acquire a carbon-glass surface due to rapid evaporative cooling. Nanotubes crystallize inside the supercooled, glass-coated liquid-carbon drops. The carbon-glass layer ultimately coats and beads on the nanotubes near the surface.

Journal Article↗

PubMed2004

Epigenetic silencing of the CIITA gene and posttranscriptional regulation of class II MHC genes in ocular melanoma cells.

PURPOSE: Primary uveal melanocytes and many ocular melanoma cells are resistant to interferon (IFN)-gamma-mediated induction of major histocompatibility complex (MHC) class II molecule expression. This suppression of class II MHC induction is considered to be one of the ways in which the eye is able to inhibit inflammatory responses. However, the mechanism(s) of this suppression is unknown. In this study, we have probed the molecular basis of this phenotype and report two distinct mechanisms underlying this phenotype. METHODS: Primary ocular melanocytes and ocular melanoma cell lines (retaining this IFN-gamma-resistant class II MHC phenotype) were examined for the expression of class II MHC molecules on the cell surface by flow cytometry. Class II MHC gene expression was further examined using Western blot and reverse transcriptase-polymerase chain reaction (RT-PCR) analyses. RESULTS: The IFN-gamma signal-transduction pathway was found to be intact by electrophoretic mobility shift assay (EMSA) and transfection of reporter constructs. The lack of class II MHC gene expression appears to result from at least two mechanisms: (1) a specific inhibition of CIITA (class II transactivator) gene expression (reminiscent of trophoblasts), and (2) posttranscriptional regulation of class II MHC genes. CONCLUSIONS: The inability of primary uveal melanocytes and ocular melanoma cells to express class II MHC molecules after treatment with IFN-gamma has been found to map to two distinct points in the class II MHC biosynthetic pathway. The predominant mechanism appears to involve the silencing of the endogenous gene encoding the class II transactivator (CIITA). Here, the blockade does not involve signal transduction from the IFN-gamma receptor, but rather involves a specific silencing of the CIITA gene. A second mechanism involves the posttranscriptional regulation of class II MHC genes.

Cell Nucleus↗

PubMed2002

[Study on micro-hardness and wear resistance of human tooth at different depth].

Micro-hardness of human teeth was measured by micro hardnessmentry at different depths i.e. enamal, enamelo-dentinal junction and dentin. A simulated dental friction test was conducted of respectively in these three areas, opposing pure titanium ball under a modified fretting machine. The results showed that micro-hardness is 320.40 +/- 22.77 HV of enamal, 232.26 +/- 32.31 HV of enamelo-dentinal junction, and 61.17 +/- 9.42 HV of dentin (P < 0.05). Wear depth is 17.33 +/- 0.58 microns of enamal, 49.44 +/- 16.47 microns of enamelo-dentinal junction and 95.20 +/- 15.07 microns of dentin(P < 0.05). Wear resistance of enamal is much better than that of dentin's. This preliminary investigation should be very useful in clinical applications.

Adult↗