RESUMO
The existence of a ferroelectric fluid phase for systems of 1000-2000 dipolar hard or soft spheres is well established by numerical simulations. Theoretical approaches proposed to determine the stability of such a phase are either in qualitative agreement with the simulation results or disagree with them. Experimental results for systems of molecules or particles with large electric or magnetic dipole moments are also inconclusive. As a contribution to the question of existence and stability of a fluid ferroelectric phase this simulation work considers system sizes of the order of 10 000 particles, thus an order of magnitude larger than those used in previous studies. It shows that although ferroelectricity is not affected by an increase of system size, different spatial arrangements of the dipolar hard spheres in such a phase are possible whose free energies seem to differ only marginally.
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We investigate, by Monte Carlo simulation, the effect of the steepness of the short range repulsive potential on mesostructure formation in dipolar particles submitted to a strong external field. Columnar clusters made of several dipolar chains are only observed when the short-range potential is sufficiently steep. The confinement of the dipolar liquid in a slit geometry instead of bulk conditions suppresses the formation of columns.
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Mesostructures formed by dipolar particles confined between two parallel walls and subjected to an external field are studied by Monte Carlo simulations. The main focus of the work is the structural behavior of the Stockmayer fluid in the low density regime. The dependence of cluster thickness and ordering is estimated as a function of density and wall separation, the two most influential parameters, for large dipole moments and high field strengths. The great sensitivity of the structure to details of the short-range part of the interactions is pointed out. In particular, the attractive part of the Lennard-Jones potential is shown to play a major role in driving chain aggregation. The effect of confinement, evaluated by comparison with results for a bulk system, is most pronounced for a short range hard sphere potential. No evidence is found for a novel "gel-like" phase recently uncovered in low density dipolar colloidal suspensions [A. K. Agarwal and A. Yethiraj, Phys. Rev. Lett. 102, 198301 (2009)].
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Human complement receptor type 2 (CR2) is the B lymphocyte receptor for C3d and the Epstein-Barr virus. This protein is also a member of a family of C3b/C4b binding proteins that regulate complement activation, comprise tandemly repeated 60-75 amino acid sequences, and whose genes map to band q32 on chromosome 1. Overlapping cDNA clones encoding the entire human CR2 protein have been isolated from a human tonsillar cDNA library. The derived amino acid sequence of 1,032 residues encodes a peptide of 112,716 mol wt. A signal peptide was identified, followed by 15 copies of the short consensus repeat (SCR) structure common to the C3/C4 binding protein family. The entire extracellular portion of the protein comprised SCRs, thus, the ligand binding sites both for C3d and the EBV protein gp350/220 are positioned within this structure. Immediately following the final SCR was a transmembrane sequence of 24 amino acids and a cytoplasmic region of 34 amino acids. One of five cDNA clones isolated contained an additional SCR, providing evidence for alternative mRNA splicing or gene products of different human alleles. The CR2 cDNAs were used to isolate CR2-specific genomic phage. The entire CR2 coding sequences were found within 20 kb of human DNA. Analysis of the CR2 cDNA sequence indicated that CR2 contained internally homologous regions and suggested that CR2 arose by duplication of a primordial gene sequence encoding four SCRs. Comparison of the CR2 peptide sequence with those of other members of the gene family has identified many regions highly homologous with human CR1, fewer with C4bp and decay accelerating factor, and very few with factor H, and suggested that CR2 and CR1 arose by duplication of the same ancestral gene sequence. The homology between CR2 and CR1 extended to the transmembrane and cytoplasmic regions, suggesting that these sequences were derived from a common membrane-bound precursor.
Assuntos
Linfócitos B/análise , Receptores de Complemento/genética , Receptores Virais/genética , Sequência de Aminoácidos , Sequência de Bases , Proteínas de Transporte/genética , Complemento C3/metabolismo , Complemento C4/metabolismo , DNA/genética , Herpesvirus Humano 4/metabolismo , Humanos , Integrina alfaXbeta2 , Dados de Sequência Molecular , Receptores de Complemento 3b , Receptores de Complemento 3d , Homologia de Sequência do Ácido NucleicoRESUMO
A pillared interlayered clay is represented by a two-dimensional quenched charged disordered medium, in which the pillar configuration is produced by the quench of a two-dimensional electrolyte and the subsequent removal of the anions (that act as a template). The cation charge is counterbalanced by a neutralizing background that is an ideal representation of the layer's negative charge in the experimental system. In this paper we investigate the adsorption of electrolyte particles in this charged disordered medium resorting both to the use of the replica Ornstein-Zernike equation in the hypernetted chain approximation and grand canonical Monte Carlo simulations. The theoretical approach qualitatively reproduces the simulated behavior of the adsorbed fluids. Theoretical estimates of the material porosities obtained for various types of pillar distributions are in good agreement with the simulation. We investigate the influence of the matrix on correlation functions and adsorption isotherms.
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Monte Carlo simulations of a Stockmayer fluid confined between two parallel walls are performed to investigate self-organization of magnetic nanocrystals in a field parallel to the walls as a function of density, field strength, and wall separation. In order to study the formation of mesoscopic structures, a large number of up to 12,000 particles have to be used. The particles organize into periodically spaced cylindrical-like columns whose width typically varies between 5 and 9 particle diameters at low density. At small heights the columns are quenched due to the parallel walls, while larger wall separations can accommodate several layers of columns in good agreement with experiments. An increase in density entails a clear increase in column thickness, whereas an increase in field strength seems to have the opposite effect.
Assuntos
Método de Monte Carlo , Nanopartículas/química , Magnetismo , Propriedades de SuperfícieRESUMO
PURPOSE: This study reviewed the literature regarding mesh migration in abdominal hernia repair. The aim of this study is to interrogate incidence, common type of abdominal hernia repair leading to migration, patterns of mesh migration, and materials associated with migration. METHODS: A comprehensive literature review was conducted. PubMed and MEDLINE were searched for relevant articles in the English literature. We employed Ovid syntax from 1949 to January 2010, the Cochrane Library, Google and Google Scholar. The clinical trial database Clinicaltrials.gov was reviewed. Letters to the editor were reviewed to extract cross-references. Multiple keywords were used alone and in combination to extract all relevant articles. RESULTS: In total, 287 unique English citations were reviewed. Of these, 84 articles were selected and consisted of 3 case series, 77 case reports, 2 literature reviews, 1 retrospective study, and 1 prospective, observational study. In an analysis of available cases, the average age was 59.8 ± 13.8 years with a male predominance (76.2%). The index hernia repair was inguinal in 62.9%, incisional/ventral in 28.1%, umbilical in 6.7%, and other in 2.2%. Within the inguinal hernia group, 51.8% were open repairs, 42.9% were laparoscopic, and 1.8% were robotic. Implicated mesh materials included polypropylene, PTFE, and composite mesh. Migration commonly affected multiple organs (31.5%). CONCLUSIONS: It is likely that more cases of mesh migration will appear in the literature. Reports are heterogeneous and highlight the diversity of this complication. A standardized method of reporting is needed to develop guidelines and recommendations for this presentation.
Assuntos
Migração de Corpo Estranho , Hérnia Abdominal/cirurgia , Herniorrafia/efeitos adversos , Telas Cirúrgicas/efeitos adversos , Migração de Corpo Estranho/etiologia , Migração de Corpo Estranho/terapia , Herniorrafia/métodos , HumanosRESUMO
B-cell development occurs in a stepwise fashion that can be followed by the expression of B cell-specific surface markers. In this study, we wished to identify proteins that could contribute to the changes in expression of such markers. By using RNA from freshly isolated B220+ cells, we hoped to reduce the effect of artifacts that occur during the isolation and amplification steps necessary to use flow cytometry analysis-sorted subsets in microarray experiments. Analyses comparing expression patterns from B220+ 2-week bone marrow (pro-B, pre-B, immature B cells), 2-week spleen (predominantly transitional cells) and 8-week spleen (mainly mature B cells) yielded hundreds of genes. We also examined the B cell-activating factor (BAFF)-dependent effects on immature splenic B cells by comparing expression patterns in the spleen between 2-week A/J vs 2-week A/WySnJ mice, which lack functional BAFF receptor signaling. Genes that showed the expression differences between spleen and bone marrow samples were then analyzed through quantitative PCR on B-cell subsets isolated using two different sorting protocols. A comparison of the results from our study with the results from other analyses showed not only some overlap of preferentially expressed genes but also an expansion of other genes potentially involved in B-cell development.
Assuntos
Fator Ativador de Células B/genética , Receptor do Fator Ativador de Células B/genética , Subpopulações de Linfócitos B/metabolismo , Células da Medula Óssea/metabolismo , Diferenciação Celular/genética , Baço/metabolismo , Animais , Fator Ativador de Células B/imunologia , Fator Ativador de Células B/metabolismo , Receptor do Fator Ativador de Células B/imunologia , Receptor do Fator Ativador de Células B/metabolismo , Subpopulações de Linfócitos B/imunologia , Células da Medula Óssea/imunologia , Diferenciação Celular/imunologia , Perfilação da Expressão Gênica , Camundongos , Camundongos Endogâmicos , Análise de Sequência com Séries de Oligonucleotídeos , Transdução de Sinais , Baço/imunologia , Transcrição GênicaRESUMO
To understand the self-organization of magnetic nanocrystals in an applied field, we perform Monte Carlo simulations of Stockmayer fluids confined between two parallel walls. The system is examined in the gas-liquid coexistence region of its phase diagram and the field is applied perpendicular to the walls. Gibbs ensemble simulations are carried out to determine the phase coexistence curves of the confined Stockmayer fluid. In canonical simulations, different types of organizations appear dependent on particle density: columns, walls, and elongated and spherical holes. The morphology and size of structures are in good agreement with results obtained by free energy minimization and experiments. The influence of a distribution of particle sizes on the particle organization is investigated.
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Microbial adhesion to the host tissue represents an early, critical step in the pathogenesis of most infectious diseases. BORRELIA: burgdorferi, the causative agent of Lyme disease (LD), expresses two surface-exposed decorin-binding adhesins, DbpA and DbpB. A decorin-deficient (Dcn(-/-)) mouse was recently developed and found to have a relatively mild phenotype. We have now examined the process of experimental LD in Dcn(-/-) mice using both needle inoculation and tick transmission of spirochetes. When exposed to low doses of the infective agent, Dcn(-/-) mice had fewer Borrelia-positive cultures from most tissues analyzed than did Dcn(+/+) or Dcn(+/-) mice. When the infection dose was increased, similar differences were not observed in most tissues but were seen in bacterial colonization of joints and the extent of Borreila-induced arthritis. Quantitative PCR demonstrated that joints harvested from Dcn(-/-) mice had diminished Borrelia numbers compared with issues harvested from Dcn(+/+) controls. Histological examination also revealed a low incidence and severity of arthritis in Dcn(-/-) mice. Conversely, no differences in the numbers of Borreila-positive skin cultures were observed among the different genotypes regardless of the infection dose. These differences, which were observed regardless of genetic background of the mice (BALB/c or C3H/HeN) or method of infection, demonstrate the importance of decorin in the pathogenesis of LD.
Assuntos
Grupo Borrelia Burgdorferi/patogenicidade , Proteoglicanas/fisiologia , Animais , Grupo Borrelia Burgdorferi/imunologia , Decorina , Modelos Animais de Doenças , Proteínas da Matriz Extracelular , Feminino , Imunidade Inata , Ixodes , Doença de Lyme/imunologia , Doença de Lyme/microbiologia , Doença de Lyme/patologia , Masculino , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Endogâmicos C3H , Camundongos Knockout , Proteoglicanas/genética , Proteoglicanas/imunologiaRESUMO
Persistence of the Lyme disease spirochete, Borrelia burgdorferi, in the presence of an active immune response has been well documented. Evidence from the past year indicates that modulation of surface antigens by the spirochete may be a major mechanism for evading the immune response.
Assuntos
Portador Sadio/imunologia , Eritema Migrans Crônico/prevenção & controle , Doença de Lyme/imunologia , Doença de Lyme/patologia , Animais , Portador Sadio/patologia , Eritema Migrans Crônico/imunologia , Eritema Migrans Crônico/patologia , Humanos , Imunidade Inata/imunologia , Doença de Lyme/prevenção & controle , Fatores de TempoRESUMO
Monte Carlo computer simulations of a quasi two-dimensional (2D) dipolar fluid at low and intermediate densities indicate that the structure of the fluid is well described by an ideal mixture of self-assembling clusters. A detailed analysis of the topology of the clusters, of their internal energy and of their size (or mass) distributions is used to obtain approximations to their partition functions. Within the scope of these approximations, the results of this work suggest that the 2D dipolar fluid undergoes a phase transition from a dilute phase characterized by a number of disconnected clusters to a condensed phase characterized by a network or spanning (macroscopic) cluster that includes most of the particles in the system.
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Recent studies have confirmed the infectious and inflammatory nature of arthritis induced by Borrelia burgdorferi, or Lyme arthritis. This arthritis is directed by the presence of the bacteria in joint tissue, and is mediated through activation of the Toll-like receptor 2 (TLR2) signaling pathways by borrelial lipoproteins. Several host genes regulate the severity of arthritis, possibly by regulating the balance of pro- and anti-inflammatory responses.
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Artrite Infecciosa/etiologia , Grupo Borrelia Burgdorferi , Doença de Lyme/fisiopatologia , Animais , Artrite Infecciosa/imunologia , Artrite Infecciosa/microbiologia , Grupo Borrelia Burgdorferi/imunologia , Modelos Animais de Doenças , Lipoproteínas/imunologia , Doença de Lyme/imunologia , CamundongosRESUMO
The microphthalmic (mi) mouse possesses a dominant negative mutation in the microphthalmia-associated transcript factor (MITF) transcription factor. These animals are characterized by reduced numbers of peripheral mast and natural killer (NK) cells, are osteopetrotic because of osteoclast reduction and malfunction, lack functional melanocytes, and are deficient for maturing B-cells within the bone marrow. Granulocyte precursor cells, however, are functionally maintained within the mi bone marrow. A central question has been whether the B-cell deficiency of the mi mouse marrow is caused by the absence of an MITF-controlled gene product or because of the compromised, osteopetrotic environment. In this report, we examined mi marrow by performing transcriptional mapping analyses of candidate genes whose products are instrumental for functional osteoclast and B-cell development. Surprisingly, the expression of a subset of such genes including RANKL, stromal-derived factor (SDF-1), B-cell lymphotactin chemokine (BLC), and RANK was dramatically enhanced in the mi marrow. Normal and mutant marrow were also analyzed by subtractive transcript cloning, which identified a number of known and unknown genes with altered transcriptional activity. One such unknown mouse gene possesses a human counterpart that is interferon-beta (IFN-beta) inducible, suggesting the osteopetrotic marrow is enriched for IFN-beta, a cytokine that is known to eliminate B-cell precursors. A model is proposed suggesting excess RANKL sets off a cascade of cytokine production including IFN-beta that leads to the preferential elimination of B-cell precursors in the marrow of osteopetrotic marrow.
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Linfócitos B/metabolismo , Proteínas de Transporte/fisiologia , Interferon beta/metabolismo , Glicoproteínas de Membrana/fisiologia , Microftalmia/genética , Sequência de Aminoácidos , Animais , Células da Medula Óssea , Fêmur/patologia , Perfilação da Expressão Gênica , Genótipo , Macrófagos/metabolismo , Camundongos , Microftalmia/metabolismo , Modelos Biológicos , Dados de Sequência Molecular , Osteoclastos/metabolismo , Ligante RANK , RNA/metabolismo , Receptor Ativador de Fator Nuclear kappa-B , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Homologia de Sequência de Aminoácidos , Fatores de Tempo , Transcrição GênicaRESUMO
The human C3d receptor (complement receptor type 2, CR2), that also serves as the B lymphocyte receptor for the Epstein-Barr virus, was purified from detergent lysates from the B lymphoblastoid cell lines, SB and Raji, by monoclonal antibody affinity chromatography using the anti-CR2 monoclonal antibody, HB-5. Relative to the concentration of cellular protein and receptor that was initially solubilized by detergent, the procedure provided a 37,000-fold purification with a 40-50% recovery of CR2. The purified receptor presented a single Coomassie blue-stained band when analyzed by SDS-PAGE, and it retained its function of binding to C3-Sepharose. The N-terminus of CR2 was blocked. The amino acid composition was significantly similar to that of the C3b/C4b receptor, factor H and C4 binding protein, suggesting that CR2 may be a member of this newly defined protein family. However, CR2 did not exhibit the regulatory functions of these proteins, namely, the decay dissociation of the classical or alternative pathway C3 convertases and serving as a cofactor for the cleavage of C3b.
Assuntos
Linfócitos B/análise , Complemento C3/metabolismo , Receptores de Complemento/isolamento & purificação , Receptores Virais/análise , Aminoácidos/análise , Anticorpos Monoclonais , Linfócitos B/imunologia , Linhagem Celular , Cromatografia de Afinidade/métodos , Fator I do Complemento , Endopeptidases/fisiologia , Herpesvirus Humano 4 , Humanos , Peso Molecular , Radioimunoensaio , Receptores de Complemento/fisiologia , Receptores de Complemento 3d , Receptores Virais/fisiologiaRESUMO
Continuous fluorescence observation of amplifying DNA allows rapid and accurate quantification of initial transcript copy number. A simple and generic method for monitoring product synthesis with the double-stranded DNA dye, SYBR Green I provides initial template copy number estimation limited only by stochastic effects. To reach this degree of sensitivity, two methods were used. First, specific products generally have a higher melting temperature than nonspecific products, and therefore, specific product formation was monitored by fluorescence acquisition at temperatures at which only specific products are double-stranded. Second, anti-Taq antibodies were used to reduce nonspecific product generation. The log-linear portion of the fluorescence vs. cycle plot was extended to determine a fractional cycle number at which a threshold fluorescence was obtained. These fractional cycle numbers were plotted against the log of starting template copies to give linear standard curves from purified PCR products, allowing easy estimation of cDNA unknowns over a 10(6)-fold range. A single template molecule per reaction could be distinguished from the absence of template, although stochastic effects increased the variance of concentration estimates below 10 copies. Above 10 copies per reaction, typical replicate coefficients of variation were 6%-37%, with better precision at higher copy numbers.
Assuntos
Corantes Fluorescentes/metabolismo , Amplificação de Genes , Compostos Orgânicos , Transcrição Gênica , Animais , Benzotiazóis , Primers do DNA/síntese química , Diaminas , Fibroblastos/química , Fator Estimulador de Colônias de Granulócitos e Macrófagos/genética , Reação em Cadeia da Polimerase/métodos , Quinolinas , Ratos , Sensibilidade e Especificidade , Membrana Sinovial/citologia , Membrana Sinovial/metabolismo , Moldes Genéticos , Transcrição Gênica/genéticaRESUMO
The authors have developed a simple, nested polymerase chain reaction (PCR) assay for amplification of an outer surface protein A (OspA) gene fragment of Borrelia burgdorferi using rapid temperature cycling and ethidium bromide detection on agarose gels, and applied it to the diagnosis of Lyme disease in humans. With denaturing and annealing temperature spikes instead of holds, cycle times were less than 20 minutes for a 30-cycle amplification. Using this rapid cycle PCR technique, as few as 5 spirochetes per mL of phosphate buffered saline were detected. In addition, B burgdorferi DNA was detected from spirochetes that had been spiked into one of several types of human body fluids including serum, synovial fluid, and cerebrospinal fluid (CSF). A number of clinical samples, which had been tested for Lyme immunoglobulin M (IgM) and immunoglobulin G (IgG) antibody were also examined. In 29 serologic positive samples (14 IgG and IgM positive, 9 IgM alone and 6 IgG alone), B burgdorferi DNA was not detected. In contrast, nine serum samples and one synovial fluid from patients with definite clinical features of Lyme disease were found to be negative by EIA and Western blot analysis for IgG and IgM antibody, but contained B burgdorferi DNA, as detected by PCR. Polymerase chain reaction analysis of serum and synovial fluid may be of significant diagnostic value in Lyme disease, especially in the absence of a serologic response in early, partially treated and seronegative chronic disease. This is the first study to report an association between PCR positivity and the absence of a serologic response to Lyme borreliosis.
Assuntos
Doença de Lyme/diagnóstico , Reação em Cadeia da Polimerase/métodos , Sequência de Bases , Grupo Borrelia Burgdorferi/isolamento & purificação , DNA Bacteriano/análise , DNA Bacteriano/sangue , Eletroforese em Gel de Ágar , Humanos , Doença de Lyme/genética , Doença de Lyme/patologia , Dados de Sequência Molecular , Sensibilidade e EspecificidadeRESUMO
Structural and thermodynamic properties of a homonuclear hard dumbbell fluid adsorbed into a disordered hard sphere matrix are studied by means of integral equation techniques and computer simulation. In particular, we have rewritten the replica Ornstein-Zernike equations to deal with orientational degrees of freedom and we have solved them in two different approaches: the hypernetted chain equation and a semiempirical extension of Verlet's approximation. We have also derived direct expressions to calculate the chemical potential in these approximations. Comparison with grand canonical Monte Carlo results shows that both theoretical treatments describe adequately the physical behavior of the system, Verlet's approach being, however, clearly superior in accordance with previous findings for equilibrated hard core mixtures.
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The phase behavior of a binary symmetric fluid in thermal equilibrium with a porous matrix has been studied with the optimized random phase approximation and grand canonical Monte Carlo simulations. Depending on the matrix properties and the matrix-fluid and fluid-fluid interactions we find three types of phase diagram characterized by a tricritical point, a tricritical point with a triple point, or a critical end point. Small changes in the properties of the matrix or in the interactions are demonstrated to lead to drastic modifications of the phase diagram of the fluid, in qualitative agreement with observations in experimental studies. We show, in particular, that the change between the different types of phase diagram is triggered not only by the fluid-fluid interactions (internal parameters) but also by the properties of the matrix and of the matrix-fluid potentials (external parameters).
RESUMO
We studied a quasi-two-dimensional dipolar fluid in the chaining regime using Monte Carlo canonical simulations and theoretical analyses. The self-assembled clusters were characterized by measuring their internal energy, conformational properties, and equilibrium length distributions. We generalized and used equilibrium polymer theory to describe the structure of the chains and rings observed in the simulations. The scaling forms of the length distribution functions predicted by theory were found to describe adequately the simulation results. Finally, we discuss how this type of analysis may be used to establish the existence and mechanisms of phase transitions in dilute dipolar fluids.