Biomedical subjects
Publications and source records attributed to X S Chen.
Up to now, none of the previously derived expressions is usable in simulations for the practical calculation of the thermodynamic pressure of a fluid adsorbed in a random porous medium. A bona fide virial expression of this pressure is presented. Contrary to what was believed, we show that this pressure is a measurable quantity and propose an experimental procedure for its measurement.
We study the bulk and finite-size critical behavior of the O(n) symmetric phi4 theory with spatially anisotropic interactions of noncubic symmetry in d<4 dimensions. In such systems of a given (d,n) universality class, two-scale factor universality is absent in bulk correlation functions, and finite-size scaling functions including the Privman-Fisher scaling form of the free energy, the Binder cumulant ratio, and the Casimir amplitude are shown to be nonuniversal. In particular it is shown that, for anisotropic confined systems, isotropy cannot be restored by an anisotropic scale transformation.
OBJECTIVE: To report the epidemiological trends of leprosy in China from 1949 to 1998. METHOD: Data for the study were obtained from the computerized database of the National System of Leprosy Surveillance. FINDINGS: A total of 474,774 leprosy patients were detected during this 50-year period. Case detection rates per 100,000 population were highest in the 1950s and 1960s, with peaks appearing in 1957-58, 1963-66, 1969-70, and 1983-84, corresponding to mass surveys or screening surveys carried out in most areas or selected areas of the country. While the duration of the disease at the time of detection fell over the period, the disability rates, which were > 50% in the early 1950s, have decreased gradually to 20.8% by 1997-98 but are still too high. More than 50% of cases were found through active methods in the periods 1955-58, 1965-66, and 1969-76, but in recent years cases are mostly detected through dermatological clinics or by voluntary reporting. The peak prevalences of the 1960s (i.e. > 2 per 10,000 population) decreased annually from the 1970s onwards. By the end of 1998 the prevalence was 0.05 per 10,000 population. CONCLUSIONS: This study shows that leprosy was well controlled in China and that the WHO goal of elimination of leprosy as a public health problem has been achieved at the national and subnational levels. However, leprosy is still unevenly distributed in the country. According to the criterion for leprosy elimination in China--defined as a prevalence of < 1 per 100,000 in county or city--there are still more than 10% of counties or cities where this target has not yet been reached. Special attention must therefore be given to achieve elimination and final eradication of leprosy in China.
We calculate finite-size effects of the Gaussian model in a Lx(d-1) box geometry with free boundary conditions in one direction and periodic boundary conditions in d-1 directions for 2 infinity ). Finite-size scaling is found to be valid for d<3 and d>3 but logarithmic deviations from finite-size scaling are found for the free energy and energy density at the Gaussian upper borderline dimension d*=3. The logarithms are related to the vanishing critical exponent 1-alpha-nu=(d-3)/2 of the Gaussian surface energy density. The latter has a cusplike singularity in d>3 dimensions. We show that these properties are the origin of nonscaling finite-size effects in the mean spherical model with free boundary conditions in d > or =3 dimensions. At bulk T(c), in d=3 dimensions we find an unexpected nonlogarithmic violation of finite-size scaling for the susceptibility chi approximately L3 of the mean spherical model in film geometry, whereas only a logarithmic deviation chi approximately L2 ln L exists for box geometry. The result for film geometry is explained by the existence of the lower borderline dimension d(l)=3, as implied by the Mermin-Wagner theorem, that coincides with the Gaussian upper borderline dimension d*=3. For 3 or =T(c).
The singular part of the finite-size free-energy density f(s) of the O(n) symmetric phi(4) field theory is calculated for confined geometries of linear size L with periodic boundary conditions in the large-n limit and with Dirichlet boundary conditions in one-loop order. We find that both a sharp cutoff and a subleading long-range interaction cause a leading nonuniversal L dependence of f(s) near T(c). This implies a significant restriction for the validity of universal finite-size scaling for model systems and real systems. For film geometry we predict a leading nonuniversal contribution to the critical Casimir force above the superfluid transition of (4)He.
BACKGROUND: Herpes simplex facialis/labialis (HSFL) is a common infectious skin disorder, caused mainly by herpes simplex virus (HSV) type 1, for which the topical application of a cream containing an antiviral agent for treatment of the disease has been widely utilized. OBJECTIVE: To explore the efficacy of the topical application of 1% penciclovir cream in the treatment of HSFL, and to compare its efficacy and safety with 3% aciclovir cream. METHODS: A total of 248 patients with a diagnosis of HSFL were randomly allocated to one of the two treatment groups (n = 124 each), using stratified randomization based on a table of random numbers. Before treatment (day 0) and at every visit (days 3, 5 and 7) during the study, the sign and symptom scores were recorded by the same doctor. RESULTS: Excluding 23 patients (10 in the penciclovir and 13 in the aciclovir groups), 225 completed the study, and no severe adverse events were noted with any of the treatment regimens. Results show that an encouraging improvement in the clinical course was found simultaneously for patients with each episode type and each treatment assignment. There were no significant differences in terms of efficacy endpoint, clinical cure rate, and safety between the two treatment arms, but there was a trend towards a shorter time to resolution of all symptoms, cessation of new blisters, and loss of crust (p <or= 0.08) in penciclovir-treated primary patients. In addition, the clinical scores in penciclovir-treated primary patients were significantly lower than those in the respective aciclovir-treated patients on treatment day 5 (p < 0.01) and day 7 (p < 0.05). CONCLUSION: Topical 1% penciclovir cream is as convenient and as effective as 3% aciclovir cream for the treatment of HSFL. Penciclovir cream may provide a good topical alternative to other types of therapy in the future.
Complement receptor type 2 (CR2)/CD21 is a B lymphocyte cell membrane C3d/iC3b receptor that plays a central role in the immune response. Human CR2 is also the receptor for the EBV viral membrane glycoprotein gp350/220. Both C3d and gp350/220 bind CR2 within the first two of 15-16 repetitive domains that have been designated short consensus/complement repeats. Many mAbs react with human CR2; however, only one currently available mAb is known to block both C3d/iC3b and gp350/220 binding. We have used a recombinant form of human CR2 containing the short consensus/complement repeat 1-2 ligand-binding fragment to immunize Cr2(-/-) mice. Following fusion, we identified and further characterized four new anti-CR2 mAbs that recognize this fragment. Three of these inhibited binding of CR2 to C3d and gp350/220 in different forms. We have determined the relative inhibitory ability of the four mAbs to block ligand binding, and we have used overlapping peptide-based approaches to identify linear epitopes recognized by the inhibitory mAbs. Placement of these epitopes on the recently solved crystal structure of the CR2-C3d complex reveals that each inhibitory mAb recognizes a site either within or adjacent to the CR2-C3d contact site. One new mAb, designated 171, blocks CR2 receptor-ligand interactions with the greatest efficiency and recognizes a portion of the C3d contact site on CR2. Thus, we have created an anti-human CR2 mAb that blocks the C3d ligand by direct contact with its interaction site, and we have provided confirmatory evidence that the C3d binding site seen in its crystal structure exists in solution.
We perform a one-loop calculation of the strange quark polarization (Deltas) of the nucleon in an SU(3) chiral potential model. We find that if the intermediate quark excited states are summed over in a proper way, i.e., summed up to a given energy instead of given radial and orbital quantum numbers, Deltas turns out to be almost independent of all the model parameters: quark masses and potential strengths. The contribution from the quark-antiquark pair creation and annihilation " Z" diagrams is found to be significant. Our numerical results agree quite reasonably with experiments and lattice QCD calculations.
Complement receptor 2 (CR2/CD21) is an important receptor that amplifies B lymphocyte activation by bridging the innate and adaptive immune systems. CR2 ligands include complement C3d and Epstein-Barr virus glycoprotein 350/220. We describe the x-ray structure of this CR2 domain in complex with C3d at 2.0 angstroms. The structure reveals extensive main chain interactions between C3d and only one short consensus repeat (SCR) of CR2 and substantial SCR side-side packing. These results provide a detailed understanding of receptor-ligand interactions in this protein family and reveal potential target sites for molecular drug design.
The L1 major capsid proteins of human papillomavirus (HPV) types 11 and 16 were purified and analyzed for structural integrity and in vitro self-assembly. Proteins were expressed in Escherichia coli as glutathione-S-transferase-L1 (GST-L1) fusions and purified to near homogeneity as pentamers (equivalent to viral capsomeres), after thrombin cleavage from the GST moiety and removal of tightly associated GroEL protein. Sequences at the amino and carboxy termini contributing to formation of L1 pentamers and to in vitro capsid assembly were identified by deletion analysis. For both HPV11 and HPV16 L1, up to at least ten residues could be deleted from the amino terminus (Delta N10) and 30 residues from the carboxy terminus (Delta C30) without affecting pentamer formation. The HPV16 pentamers assembled into relatively regular, 72-pentamer shells ("virus-like particles" or VLPs) at low pH, with the exception of HPV16 L1 Delta N10, which assembled into a 12-pentamer, T=1 capsid (small VLP) under all conditions tested. The production of large quantities of assembly-competent L1, using the expression and purification protocol described here, has been useful for crystallographic analysis, and will be valuable for studies of virus-receptor interactions and potentially for vaccine design.
5-Lipoxygenase is the key enzyme in the formation of leukotrienes, which are potent lipid mediators of asthma pathophysiology. This enzyme translocates to the nuclear envelope in a calcium-dependent manner for leukotriene biosynthesis. Eight green fluorescent protein (GFP)-lipoxygenase constructs, representing the major human and mouse enzymes within this family, were constructed and their cDNAs transfected into human embryonic kidney 293 cells. Of these eight lipoxygenases, only the 5-lipoxygenase was clearly nuclear localized and translocated to the nuclear envelope upon stimulation with the calcium ionophore. The N-terminal "beta -barrel" domain of 5-lipoxygenase, but not the catalytic domain, was necessary and sufficient for nuclear envelope translocation. The GFP-N-terminal 5-lipoxygenase domain translocated faster than GFP-5-lipoxygenase. beta-Barrel/catalytic domain chimeras with 12- and 15-lipoxygenase indicated that only the N-terminal domain of 5-lipoxygenase could carry out this translocation function. Mutations of iron atom binding ligands (His550 or deletion of C-terminal isoleucine) that disrupt nuclear localization do not alter translocation capacity indicating distinct determinants of nuclear localization and translocation. Moreover, data show that GFP-5-lipoxygenase beta-barrel containing constructs can translocate to the nuclear membrane whether cytoplasmic or nuclear localized. Thus, the predicted beta-barrel domain of 5-lipoxygenase may function like the C2 domain within protein kinase C and cytosolic phospholipase A(2) with unique determinants that direct its localization to the nuclear envelope.
BACKGROUND: Surveys of the prevalence of atopic dermatitis (AD) have been carried out world-wide, but the results vary widely. The differences probably result from the use of different diagnostic criteria. Williams et al. proposed minimum, simplified, diagnostic criteria that require no invasive test and are easy to use. Pilot studies in European countries showed their suitability for implementation both in hospitals and in the community, and their high sensitivity and specificity. OBJECTIVES: To evaluate the potential practical value of the criteria of Williams et al. in the Chinese population. METHODS: The criteria of Hanifin and Rajka (gold standard), Williams et al. and Kang and Tian were applied and compared in 111 patients with AD and 121 control subjects with other skin diseases in three out-patient centres in China. RESULTS: The criteria of Williams et al. showed a similar diagnostic efficiency to that of the gold standard, with the sensitivity, specificity and kappa value reaching 95.50%, 97.52% and 0.93, respectively. No significant difference was found between the criteria of Williams et al. and those of Kang and Tian (chi2 = 0.69, P > 0.05). 'Onset under the age of 2 years', a criterion of Williams et al. could be used in subjects of any age. CONCLUSIONS: The diagnostic efficiency of the criteria of Williams et al. was basically similar to those of Hanifin and Rajka and of Kang and Tian in our out-patient settings. However, those of Williams et al. were easier to apply and required no invasive tests.
A new cerebroside, named typhonoside (1), was isolated from the root tuber of Typhonium giganteum Engl. along with three known compounds dipalmitin (2), alpha-monopalmitin (3) and 2,6-diamino-9-beta-D-ribofuranosylpurine (4). The structure of 1 was determined to be 1-O-beta-D-glucopyranosyl-(2S,3S,4R,8Z)-2-[(2'-hydroxyl-docosanoyl)amino]-8-otadecene-1,3,4-triol on the basis of spectral data.
AIM: To investigate the anti-HBV effect of oxymatrine (oxy) in vivo. METHODS: HBV transgenic mice were produced by micro-injection of a 4.2 kb fragment containing the complete HBV genomes. Expression level of HBsAg and HBcAg in the transgenic mice liver was determined by immunohistochemical assay. RESULTS: Four groups (6 mice in each group) were injected intraperitoneally with oxy at the dosage of 100, 200, and 300 mg/kg or with saline once a day for 30 days. Both HBsAg and HBcAg were positive in livers of all the six mice in the control group (injected with saline), and were positive in livers of two mice in 100mg/kg group and 300 mg/kg group. In 200 mg/kg group, HBsAg and HBcAg were negative in livers of all the six mice. Based on the results, 200mg/kg is the ideal dosage to explore the effect of oxy at different time points. According to the oxy treatment time, mice were divided into four groups: 10 d, 20 d, 30 d and 60 d (4 mice in each group). Each mouse underwent liver biopsy two weeks before the treatment of oxy. Down-regulation of HBsAg and HBcAg appeared after treatment of oxymatrine for 10 d and 20 d, Dane-like particles disappeared after the treatment of oxy for 20 d under electron microscopy, however, the expression level of HBsAg and HBcAg returned to normal 60 d later after oxy treatment. CONCLUSION: Oxymatrine can reduce the contents of HBsAg and HBcAg in transgenic mice liver,longer treatment time and larger dosage do not yield better effects.
Along with the nationwide economic reform initiated in the early 1980s and the rapid decrease of leprosy endemic after the implementation of multi-drug therapy (MDT), the leprosy programme changed from 'vertical' to 'horizontal'. An evolution in the mode of detection of leprosy cases has consequently taken place. Based on the nationwide registration of newly detected cases, the profile of patients at detection has been studied. The proportions of cases corrected significantly with calendar years in detection by dermatological clinics, contact checks, 'clue survey' and mass survey, showing a significant increase in percentage of cases detected through dermatological clinics and contact checks, and decreases through 'clue survey' and mass survey. Detection of cases through dermatological clinics and voluntary reporting have become the main modes of case-finding during 1997-1998, accounting for 37.3% and 28.6%, respectively, where contact check accounts for only 9.1%. In areas with good dermatological services, a significantly higher proportion (75.9%) of cases was detected through dermatological clinics, where voluntary reporting and 'clue survey' were the main modes of detection in endemic areas. As regards confirmation of diagnosis, the great majority of cases were confirmed by leprosy units, even though they were detected in various other situations. Only 6.5% of leprosy cases were detected and subsequently confirmed by doctors in dermatologic clinics. The present modes of detection and their relation to demographical, epidemiological, clinical factors and health services are discussed. This study emphasizes the cardinal importance of the dermatological clinics in the detection of leprosy cases in China at the present time and hence the need to strengthen the training of doctors in these clinics, while continuously encourage their involvement in leprosy control.
OBJECTIVE: To investigate the role of STAT1 on the regulation of human hsp90 alpha gene expression. METHODS: We first transfected Jurkat cells with the STAT1 expression construct and analyzed the expression of hsp90 alpha gene expression via quantitative RT-PCR system. Then we co-transfected the STAT1 expression construct and the CAT reporter gene driven by different length of 5' flanking sequence of hsp90 alpha gene. Western blot was carried out to detect the level of tyrosine phosphorylation in Jurkat cells with and without heat shock treatment (42 degrees C 1 h). By electrophoretic mobility shift assays (EMSA), we evaluated the DNA binding activity of a STAT1 responsible element located in the regulatory region of hsp90 alpha gene in Jurkat cell nuclear extracts. RESULTS: The mRNA level of hsp90 alpha gene in Jurkat cells was decreased when transfected by STAT1 expression construct, over-expression of STAT1 down-regulates the expression of CAT reporter gene with the present of a distal fragment from -1756 to -1463 within the 5' flanking regulatory sequences of hsp90 alpha gene. The tyrosine phosphorylation of STAT1 was detectable in Jurkat cells and increased when subjected to heat shock. Electrophoretic mobility shift assays (EMSA) results showed that STAT1 could bind to its responsible element in the regulatory region of hsp90 alpha gene. CONCLUSION: STAT1 could negatively regulate the human hsp90 alpha gene expression.
We analyze finite-size effects in a L(d) geometry above the upper critical dimension d=4 within the O(n) symmetric straight phi(4) theory on the basis of exact results for n-->infinity and one-loop results for n=1. We show that finite-size effects of the straight phi(4) continuum theory with a smooth (rather than sharp) cutoff belong to the same universality class as those of the straight phi(4) lattice theory. Our analysis predicts both universal and nonuniversal features of finite-size effects and resolves long-standing discrepancies in earlier analyses of Monte Carlo (MC) data for the d=5 Ising model. Our estimates of two fundamental length scales xi(0) and l(0) are confirmed by very recent MC data.
The papillomavirus major late protein, L1, forms the pentameric assembly unit of the viral shell. Recombinant HPV16 L1 pentamers assemble in vitro into capsid-like structures, and truncation of ten N-terminal residues leads to a homogeneous preparation of 12-pentamer, icosahedral particles. X-ray crystallographic analysis of these particles at 3.5 A resolution shows that L1 closely resembles VP1 from polyomaviruses. Surface loops contain the sites of sequence variation among HPV types and the locations of dominant neutralizing epitopes. The ease with which small virus-like particles may be obtained from L1 expressed in E. coli makes them attractive candidate components of a papillomavirus vaccine. Their crystal structure also provides a starting point for future vaccine design.