Biomedical subjects

B Liang

Publications and source records attributed to B Liang.

At least 19 recordsLinked to original sources

PubMed2005

Critical point and the nature of the pseudogap of single-layered copper-oxide Bi2Sr2-xLaxCuO6+delta superconductors.

We apply strong magnetic fields of H=28.5 to 43 T to suppress superconductivity (SC) in the cuprates Bi2Sr2-xLaxCuO6+delta (x=0.65, 0.40, 0.25, 0.15, and 0), and investigate the low temperature (T) normal state by 63Cu nuclear spin-lattice relaxation rate (1/T1) measurements. We find that the pseudogap (PG) phase persists deep inside the overdoped region but terminates at x approximately 0.05, which corresponds to the hole doping concentration of approximately 0.21. Beyond this critical point, the normal state is a Fermi liquid that persists as the ground state when superconductivity is removed by the magnetic field. A comparison of the superconducting state with the H-induced normal state in the x=0.40 (Tc=32 K) sample indicates that there remains substantial part of the Fermi surface even in the fully developed PG state, which suggests that the PG and SC are coexisting matters.

Journal Article↗

PubMed2004

Effects of milk powders in milk chocolate.

The physical characteristics of milk powders used in chocolate can have significant impact on the processing conditions needed to make that chocolate and the physical and organoleptic properties of the finished product. Four milk powders with different particle characteristics (size, shape, density) and "free" milk fat levels (easily extracted with organic solvent) were evaluated for their effect on the processing conditions and characteristics of chocolates in which they were used. Many aspects of chocolate manufacture and storage (tempering conditions, melt rheology, hardness, bloom stability) were dependent on the level of free milk fat in the milk powder. However, particle characteristics of the milk powder also influenced the physical and sensory properties of the final products.

Animals↗

PubMed2003

Two resonant magnetic modes in an overdoped high T(c) superconductor.

A detailed inelastic neutron scattering study of the overdoped high temperature copper oxide superconductor Y(0.9)Ca(0.1)Ba(2)Cu(3)O(7) reveals two-distinct magnetic resonant modes in the superconducting state. The modes differ in their symmetry with respect to exchange between adjacent copper oxide layers. Counterparts of the mode with odd symmetry, but not the one with even symmetry, had been observed before at lower doping levels. The observation of the even mode resolves a long-standing puzzle, and the spectral weight ratio of both modes yields an estimate of the onset of particle-hole spin-flip excitations.

Journal Article↗

PubMed2003

Regulatory CD8+ T cells fine-tune the myelin basic protein-reactive T cell receptor V beta repertoire during experimental autoimmune encephalomyelitis.

A significant number of self-reactive T cell clones escape thymic negative selection and are released into the periphery, where some are potentially pathogenic. The clonal expansion of self-reactive T cells is known to be limited during initial antigen encounter by apoptotic or anergic mechanisms, regulatory CD4+ T cells, and cytokines. Here we report that superimposed on these mechanisms, during the evolution of autoimmunity in experimental autoimmune encephalomyelitis (EAE), CD8+ T cells are induced, which fine-tune the peripheral self-reactive T cell receptor (TCR) repertoire. We assayed the myelin basic protein-reactive TCR repertoire in naive, EAE-recovered mice as well as EAE-recovered mice depleted of CD8+ T cells by TCRV beta surface expression, complementarity-determining region 3 length distribution, and complementarity-determining region 3 sequencing analysis. In EAE-recovered mice, certain myelin basic protein-reactive CD4+V beta 8.2+ clones are significantly decreased and this decrease is not observed if CD8+ T cells were depleted from these mice. The clones that persist in CD8+ T cell-intact mice are highly diverse in contrast to the clones expanded in CD8+ T cell-depleted mice, which are dominated by the significant outgrowth of a few clones. Importantly, the T cell clones that expand in the absence of CD8+ T cell control are enriched in potentially pathogenic self-reactive T cell clones capable of inducing EAE in vivo.

Adoptive Transfer↗

PubMed2003

Specificity and functional characteristics of anti-HLA-A mAbs LGIII-147.4.1 and LGIII-220.6.2.

Only three anti-HLA-A monoclonal antibodies (mAbs) have been described in the literature. Two of them recognize determinants shared by only a few HLA-A allospecificities. The third one, mAb 3G11, recognizes a determinant shared by most HLA-A allospecificities. Being an IgM, the latter mAb is not likely to be a useful probe in immunohistochemical reactions and in functional assays. Therefore, in the present study we have characterized the specificity of the mAbs LGIII-147.4.1 and LGIII-220.6.2. The two mAbs that do not share idiotypic determinants recognize distinct but spatially close antigenic determinants expressed on most of the gene products of the HLA-A locus. Specifically, the determinant recognized by mAb LGIII-220.6.2 is expressed on HLA-A1, -A2, -A3, -A26, -A28, -A29, -A30, -A33, -A36, -A74 and -A80 allospecificities. The determinant recognized by mAb LGIII-147.4.1, which appears to be located on the amino-acid residues 79-83 of the heavy chain, is expressed on all HLA-A allospecificities but HLA-A23, -A24, -A25 and -A32. Because of its broad reactivity, the mAb LGIII-147.4.1 was characterized in a number of assays. It was found to be a useful probe to measure the HLA-A antigen level in serum, to assess the HLA-A restriction of cytotoxic T lymphocytes (CTL) and to monitor HLA-A antigen expression in normal and malignant lesions.

Animals↗

PubMed2002

Josephson plasma resonance and phonon anomalies in trilayer Bi2Sr2Ca2Cu3O10.

The far-infrared (FIR) c axis conductivity of a Bi2223 crystal has been measured by ellipsometry. Below T(c) a strong absorption band develops near 500 cm(-1), corresponding to a transverse Josephson plasmon. The related increase in FIR spectral weight leads to a giant violation of the Ferrell-Glover-Tinkham sum rule. The gain in c axis kinetic energy accounts for a sizable part of the condensation energy. We also observe phonon anomalies which suggest that the Josephson currents lead to a drastic variation of the local electric field within the block of closely spaced CuO2 planes.

Journal Article↗

PubMed2001

Mother-to-child transmission of HIV infection and CTL escape through HLA-A2-SLYNTVATL epitope sequence variation.

Cytotoxic T lymphocytes (CTL) play a central role in containment of HIV infection. Evasion of the immune response by CTL escape is associated with progression to disease. It is therefore hypothesised that transmitted viruses encode escape mutations within epitopes that are required for successful control of viraemia. In order to test this hypothesis, escape through the dominant HLA-A2-restricted CTL epitope SLYNTVATL (p17 Gag residues 77-85 SL9) in the setting of mother-to-child-transmission (MTCT) was investigated. Initial data from two families in which the HIV-infected mother expressed HLA-A*0201 and had transmitted the virus to other family members were consistent with this hypothesis. In addition, analysis of the gag sequence phylogeny in one family demonstrated that CTL escape variants can be successfully transmitted both horizontally and vertically. To test the hypothesis further, a larger cohort of transmitting mothers (n=8) and non-transmitters (n=14) were studied. Variation within the SL9 epitope was associated with expression of HLA-A2 (P=0.04) but overall no clear link between variation from the SL9 consensus sequence and MTCT was established. However, the high level of background diversity within p17 Gag served to obscure any possible association between escape and MTCT. In conclusion, these studies highlighted the obstacles to demonstrating CTL escape arising at this particular epitope. Alternative strategies likely to be more definitive are discussed.

Amino Acid Sequence↗

PubMed2001

Infrared spectra of cis- and trans-peroxynitrite anion, OONO-, in solid argon.

The peroxynitrite anion, of vast importance in biochemistry, is formed in vivo from the reaction of NO and O(-2). Laser ablation of 10 different metal targets with concurrent 7 K codeposition of NO/Ar and O(2)/Ar mixtures gives new metal-independent infrared bands at 1458.3 and 806.1 cm(-)(1), and at 1433.3 and 983.2 cm(-1), in addition to known O(-4) and (NO)(-2) absorptions. The new bands are not observed with CCl(4) added to capture electrons or in O(2) and NO experiments without laser ablation to produce electrons, which identifies new product anions. Based on (15)NO and (18)O(2) isotopic shifts, splitting patterns in mixed isotopic experiments, and comparison with DFT isotopic frequency calculations, the former absorptions are assigned to cis-OONO-, and the latter pair to trans-OONO-, which are isolated from metal cations trapped elsewhere in the matrix. The cis- and trans-peroxynitrite anion isomers are probably formed via the ion-molecule reaction between O(-2)and NO: the O(-2) anion, made by the capture of ablated electrons, is attested by the observation of O(-4). cis- and trans-OONO- are reversibly photoisomerized by visible and near-UV radiation. Collisional stabilization of the OONO- ion-molecule dimer complex during formation of the solid argon matrix appears to be crucial.

Journal Article↗

PubMed2001

Total syntheses and biological investigations of tamandarins A and B and tamandarin A analogs.

Tamandarins A (1) and B (2), two natural products similar in structure to didemnin B (3), were recently isolated from a Brazilian marine ascidian of the family Didemnidae. The cytotoxicity of 1 was reported to be somewhat more potent in vitro than that of 3 against various human cancer cell lines. The present account describes the first total syntheses of 1 and 2, and the syntheses of tamandarin A side chain analogues. The cytotoxicity data for these compounds show that the side chain modifications exhibit a parallel effect for both didemnins and tamandarins. This observation supports tamandarins' role as didemnins' mimic.

Animals↗

PubMed2001

Total synthesis of a conformationally constrained didemnin B analog.

The total synthesis of a didemnin B analogue containing a conformationally constrained replacement for the isostatine moiety is reported. Synthetic highlights include an improved preparation of 2-hydroxy-3-cyclohexenecarboxylic acid and a new strategy for accessing the macrocycle.

Animals↗

PubMed2001

Infrared spectrum of the hyponitrite dianion, N(2)O(2)2-, isolated and insulated from stabilizing metal cations in solid argon.

Ultraviolet irradiation of a rigid 7 K argon matrix containing alkali or alkaline earth metal atoms and NO(2) isolated from each other by one or two layers of argon forms N(2)O(2)2-dianions insulated from two M(+) cations by argon atoms, and visible photolysis reverses this electron-transfer process likely involving the N(2)O(2)(-) anion intermediate. The isolated N(2)O(2)2- dianion is identified from isotopic substitution and isotopic mixtures, which show that the new 1028.5 cm(-1) metal independent absorption involves two equivalent NO subunits. DFT calculations predict a strong 1078.1 cm(-1) fundamental for the Li(NO)(2)Li molecule and isotopic frequency ratios in excellent agreement with the observed values, which provides a model for the matrix dianion system. The spectrum of solid Na(2)N(2)O(2) exhibits a 1030 cm(-1) infrared band, which strongly supports the present N(2)O(2)2- dianion assignment. The electrostatic stabilization of N(2)O(2)2-, which is probably unstable in the gas phase, is made possible by metal cations separated by one or two insulating layers of argon in the rigid 7 K matrix.

Journal Article↗

PubMed2001

Resonant spin excitation in an overdoped high temperature superconductor.

An inelastic neutron scattering study of overdoped Bi(2)Sr(2)CaCu(2)O(8+delta) ( T(c) = 83 K) has revealed a resonant spin excitation in the superconducting state. The mode energy is E(res) = 38.0 meV, significantly lower than in optimally doped Bi(2)Sr(2)CaCu(2)O(8+delta) ( T(c) = 91 K, E(res) = 42.4 meV). This observation, which indicates a constant ratio E(res)/k(B)T(c) approximately 5.4, helps resolve a long-standing controversy about the origin of the resonant spin excitation in high temperature superconductors.

Journal Article↗

PubMed2001

Structure--activity relationships of side-chain modified didemnins.

The synthesis and antitumor activity of a novel didemnin B analogue containing a psi[CH2NH] amide bond surrogate between N-Me-D-Leu7 and Pro8 are reported. The analogue shows activity (GI50 = 4 nM) comparable to that of didemnin B (GI50 = 13 nM) in the NCI-60 tumor cell screen. This result, along with new data from previously reported synthetic didemnin analogues, is discussed within the context of the side-chain SAR for didemnins.

Antineoplastic Agents↗

PubMed2001

Anti-inflammatory effects of theophylline: modulation of immune functions during murine leukemia virus infection.

LP-BM5 murine leukemia virus induces immune dysfunction leading to B cell leukemia and murine AIDS with cytokine dsyregulation. Theophylline induces apoptosis of leukemia cells in humans. Therefore the effects of theophylline on immune dysfunction in a murine model of leukemia were investigated. C57BL/6 mice consumed drinking water containing 0.3% theophylline beginning 2 weeks after murine retrovirus infection for 4 months. Theophylline largely prevented the retrovirus induced splenomagaly, lymphodenopathy, reduction in B and T cell proliferation, and suppression of Thl cytokines (IL-2) secretion. It also suppressed Th2 cytokine (IL-4, TNF-alpha, and IL-10) production, which was otherwise stimulated by retrovirus infection. These data suggest that immune dysfunction, induced by murine retrovirus infection, was largely prevented by theophylline treatment.

Animals↗

PubMed2001

Nasal-associated lymphoid tissue is a site of long-term virus-specific antibody production following respiratory virus infection of mice.

Nasal immunoglobulin A provides an initial defense against inhaled respiratory pathogens. However, it is not known whether the nasal-associated lymphoid tissues (NALT) are able to mount an effective long-lasting pathogen-specific immune response, nor is it known whether functional differences exist between the organized NALT (O-NALT) and the diffuse NALT lining the nasal passages (D-NALT). Here we show that although both the O-NALT and the D-NALT are capable of producing virus-specific antibody in response to influenza virus infection, the frequency of specific antibody-forming cells in the D-NALT is much greater than the frequency observed in the O-NALT. Furthermore, we show that the D-NALT but not the O-NALT is the site of long-term virus-specific humoral immunity which lasts for the life of the animal. These results indicate that the D-NALT is not only the major effector site of the NALT but also the site of local long-term specific antibody production.

Animals↗

PubMed2001

Lupus autoantigens: their origins, forms, and presentation.

The immune system has developed a number of mechanisms by which to distinguish self from foreign proteins. These mechanisms are found throughout the ontogeny of B and T cell development and include the deletion of autoreactive cells in central lymphoid organs and the induction of self-tolerance in the periphery. However, any failure of these mechanisms for self-tolerance may result in autoimmune disease. Efforts in our laboratory have been directed at understanding how autoimmunity is initiated and maintained in both the B and T cell compartment, with particular interest in the autoimmunity of systemic lupus erythematosus (SLE). This review will focus on our studies on the forms of self-antigens that may be involved in the original "antigenic sin" of SLE and in the role of B lymphocytes as autoantigen presenting cells. We will also discuss whether costimulation is a formal requirement for the induction and maintenance of autoimmunity. Finally, we have provided a model for how all of these individual elements may contribute to the autoimmune processes leading to pathology.

Animals↗

PubMed2001

Liquid chromatography-mass spectrometry and liquid chromatography-NMR characterization of in vitro metabolites of a potent and irreversible peptidomimetic inhibitor of rhinovirus 3C protease.

In vitro metabolism of AG7088 [trans-(4S,2'R,5'S,3"'S)-4-[2'-4-(4-fluorobenzyl)-6'-methyl-5'-[(5"-methylisoxazole-3"-carbonylamino]-4-oxoheptanoylamino]-5-(2"'-oxopyrrolidin-3-"'-yl)pent-2-enoic acid ethyl ester] was studied in liver microsomes isolated from mice, rats, rabbits, dogs, monkeys, and humans. The structures of the metabolites were characterized by liquid chromatography (LC)-tandem mass spectrometry and LC-NMR methods. Hydrolysis of the ethyl ester to produce metabolite M4 (AG7185) is the predominant pathway in all species, with the greatest activity observed in rodents and rabbits, followed by monkeys, dogs, and humans. Several hydroxylation products were identified as minor metabolites, including diastereomers M1 and M2, with a hydroxy group at the P1-lactam moiety, and M3, with a hydroxy group at the methyl position of the methylisoxazole ring. Rodent and rabbit liver microsomes formed almost exclusively the acid metabolite M4 (AG7185), with very little hydroxylated metabolites, whereas monkey liver microsomes formed more secondary metabolites (i.e., acid analogs of the hydroxylated metabolites). The overall metabolic profile of AG7088 formed in dog liver microsomes closely resembled that of human liver microsomes; therefore, this species may be the most appropriate animal model relative to humans for exposure to AG7088 and its metabolites.

3C Viral Proteases↗

PubMed2001

[Advances in the fiber coating of solid phase micro-extraction].

Solid phase micro-extraction (SPME) is a simple and effective sample preparation technique and fiber coatings play a very important role in SPME process. The discussion begins with a brief historical perspective from the very early work conducted almost a decade ago. At the moment, more than 20 alternatives of fiber coatings and size are available. In this paper, the coatings are divided into two categories: commercial fibers and custom-made fibers. A novel so-gel method has been introduced for the preparation of the coatings.

Adsorption↗