bluuebunny/crossref_metadata_2025 huggingface dataset:
The migration of Langerhans’ cells into and out of lymph nodes draining normal, carcinogen and antigen‐treated sheep skin
Authors: DANDIE GEOFFREY W. , WATKINS FRANCES Y. , RAGG SCOTT J. , HOLLOWAY PAUL E. , MULLER H. KONRAD
Published: July 2007

Epidermal Langerhans’ cell (LC) migration to the regional lymph node and beyond into central lymph was examined in sheep following topical application of the complete chemical carcinogen 7,12‐dimethylbenz(a)anthracene(DMBA)or the contact sensitizing antigen 2,4,6‐trinitrochlorobenzene (TNCB). This was facilitated by cannulating previously constructed pseudoafferent lymphatic vessels draining the skin treated with these agents or alternatively, the efferent lymphatic vessel of the regional lymph node.

Application of DMBA resulted in a biphasic increase in LC migration. There was an initial increase in LC migration at 25 h with the maximum response (3.6 × 107 LC/h) occurring approximately 5 days after DMBA treatment. In contrast, the contact sensitizing antigen TNCB caused enhanced LC migration within mitiutes of the application of antigen (3.3 × 106 LC/h) and peak migration at 8–12 h.

Examination of efferent lymph cells from the regional lymph node after DMBA treatment showed uncharacteristically large numbers of LC traversing the lymph node. These LC migration patterns suggest different mechanisms may trigger the migration of LC from skin after the application of DMBA to those associated with the normal processes of antigen presentation.
Development of T cell immune responsiveness in the chicken
Authors: LOWENTHAL JOHN W. , CONNICK TERRIE. , McWATERS PETER G. , YORK JENNIFER J.
Published: July 2007

Chickens are highly susceptible to infection by opportunistic pathogens during the first few days after hatching. This observation has generally been attributed to an immaturity of the immune system; however, the mechanisms responsible are not known.

This study investigated the ability of T cells from chickens of various ages to respond to immune stimulation. Splenic T cells were cultured in vitro and stimulated with various mitogens including Con A, PHA and monoclonal anti‐CD3 antibody. T cells obtained from adult chickens proliferated extensively and produced high levels of IL‐2, haemopoietic growth factors and IFN following stimulation. In contrast, it was found that T cells from I day old chickens failed to proliferate and secrete cytokines when similarly cultured. Reactivity to mitogens gradually developed between days 2 and 4, and by 1 week of age the level of responsiveness was equivalent to that observed with T cells obtained from adult chickens.

Whereas T cells from 1 day old chicks were found to be phenotypically mature and capable of binding mitogens as effectively as T cells from adult birds, they were functionally immature as assessed by their inability to proliferate or produce cytokines following immune stimulation. In addition, cells present in the spleen of 1 day old chicks constitutively produced a soluble inhibitor that prevented the proliferation of stimulated adult T cells. The production of inhibitor decreased dramatically by the second day post‐hatching which coincided with an enhanced ability of T cells to respond to immune stimulation. These findings suggest that the period of transient T cell unresponsiveness to immune stimulation is mediated by a functional immaturity of T cells and the production of a soluble inhibitor(s).
Heterogeneity of human anti‐Golgi auto‐antibodies: Reactivity with components from 35 to 260 kDa
Authors: KOOY JACOBA , TOH BAN‐HOCK , GLEESON PAUL A.
Published: July 2007

The Golgi auto‐antigens recognized by five human autoimmune sera were characterized with anti‐Golgi auto‐antibodies. The five sera showed strong anti‐Golgi reactivity, together with weak anti‐nuclear reactivity, as assessed by indirect immunofluorescence using the human HEp2 epithelial cell line. The Golgi auto‐antigens recognized by the autoimmune sera were identified by immunoprecipitation and immunoblotting of post‐nuclear supernatants. These sera reacted with at least 14 components of molecular mass (Mr) 35–260 kDa; three components were detected only by immunoprecipitation, six components detected only by immunoblotting and five components appear to be detected by both techniques. We have previously shown that a patient with Sjögren's syndrome has auto‐antibodies specific for a 230 kDa Golgi auto‐antigens; a bacterial fusion protein containing auto‐epitope(s) of this Golgi auto‐antigen is not recognized by the other four autoimmune sera. Taken together, this study shows that the five anti‐Golgi autoimmune sera recognize distinct sets of auto‐antigens which include both conformational and/or sequential epitopes.
Transcription of individual genes in eukaryotic cells occurs randomly and infrequently
Authors: ROSS IAN L. , BROWNE CATHERINE M. , HUME DAVID A.
Published: July 2007

Experimental evidence is presented indicating that the expression of a lacZ reporter gene driven by the HIV‐1 long terminal repeat in a series of stably transfected. cloned macrophage cell lines occurs in a very small proportion of cells. The proportion of cells expressing lacZ, rather than the level of expression in each cell, is regulated by external stimuli such as LPS and phorbol ester. Based upon these and published data we propose that transcription in eukaryotic cells occurs in short pulses interspersed by long periods of inactivity of indeterminate duration. Transcriptional regulation is envisaged as involving changes in the probability rather than the rate of transcription. A probabilistic model of transcription may explain many biological phenomena, such as stem cell division and clonogenic activity, heterogeneous gene expression among clonal cell populations, retroviral latency and cell cycle progression, which appear to involve stochastic decisions.
Characterization of a novel leucocyte activation antigen recognized by the antibody CMRF‐37
Authors: DAISH A. , HOCK B. D. , HART D. N. J.
Published: July 2007

We describe a novel activation antigen recognized by the monoclonal antibody CMRF‐37, which is absent or only weakly expressed on resting cells but is rapidly induced on T cells, B cells and monocytes following stimulation. Its kinetics of expression (12–24 h after the addition of the inductive signal) indicate that it is an early activation antigen. The cellular distribution and expression kinetics of the CMRF‐37 antigen differ from other known activation antigens and as such should be a useful marker of human leucocyte activation.
Studies on the lymphocytosis induced by pertussis toxin
Authors: MU HONG‐HUA , COOLEY MARGARET A. , SEWELL WILLIAM A.
Published: July 2007

Pertussis toxin (PT), from Bordetella pertussis, causes lymphocytosis and increased IL‐4 and IgE secretion. The lymphocytosis is associated with impaired entry of lymphocytes into lymph nodes. The dose response of PT on IL‐4 secretion was found to be similar to those for lymphocytosis and IgE production. These findings are consistent with the possibility that increased IL‐4 production by PT may be related to its effect on lymphocyte circulation. The possibility that PT may selectively influence the entry into lymph nodes of subsets identified with CD45RB, CD4 or CD8 was tested by assessing the phenotype of lymph node cells. PT had no significant effect on the proportion of cells with these markers, either in unimmunized or in immunized mice. These findings indicate that PT does not selectively impair entry of these lymphocyte subsets into lymph nodes.
Twenty years into the saga of MHC‐restriction
Authors: ADA GORDON
Published: July 2007

Twenty years ago, the terms ‘altered self and ‘H‐2 restriction’, later modified to ‘MHC‐restriction’, were coined to describe the finding by Peter Doherty and Rolf Zinkernagel that murine cytotoxic T cells (CTL) would lyse virus‐infected target cells only if effector and target cells were H‐2 compatible. This short review recalls those heady days and briefly recounts some of the later findings in three aspects of particular interest raised by the original finding: the nature of the T cell receptor, the composition and structure of the ligand on the target cell recognized by the TCR, and the importance of CTL in the control and clearance of infections in general.
Characterization of a novel leucocyte surface membrane antigen recognized by the monoclonal antibody WM65
Authors: WARD R. L. , HENNIKER A. J. , SMITH G. , BRADSTOCK K. F. , ATKINSON K. , BIGGS J. C.
Published: July 2007

WM65 is a murine mAb whieh recognizes a novel surface membrane antigen present on leukaemic and normal leucocytes. The present study further investigates the nature of this antigen, especially those features which relate to the possible therapeutic applications of the WM65 antibody. There are 1–3 × 104 molecules of this antigen present on normal leucocytes, and the same or greater numbers of antigen molecules are present on a variety of leukaemic cells. In vitro data showed that the WM65 antibody is internalized following interaction with its antigen on normal leucocytes. The affinity of this antibody was calculated using an FLISA method which required neither labelling of the antibody nor purification of the antigen and the affinity constant was found to be 3 × 107±2 × 107 (mol/L)−1. Further data are presented which suggest that this antigen is a differentiation antigen and an integral membrane protein. Despite the relatively low affinity of the WM65 antibody, a number of characteristics of the antigen suggest the antibody may possibly have therapeutic applications. These characteristics include its cellular distribution, the number of antigen molecules expressed on the cell surface and its ability to internalize in vitro.
Humoral immune responses to systemic Candida albicans infection in inbred mouse strains
Authors: COSTANTINO PAUL J. , GARE NORMAN F. , WARMINGTON JOHN R.
Published: July 2007

The protective role of humoral antibodies in the resolution of systemic candidiasis remains controversial. Investigation of the humoral immune responses in mouse strains of varying susceptibility to infection may demonstrate a link between mouse strain susceptibility, antibody production and specificity, and the ability to resolve an infection. The antibody response in five different strains of mice during a primary imune response to systemic infection with Candida albicans was investigated. Immune sera were fractionated by protein A affinity chromatography to yield fractions containing IgG l, IgG2a and IgG2b immunoglobulins. BALB/c mice of low susceptibility to the infection and DBA/2J mice of high susceptibility produced increased levels of the IgGl isotype and decreased levels of the IgG2a isotype. AKR, CBA/H and C57B1/6J mice of moderate susceptibility produced antibodies predominantly of the IgG2a isotype. The patterns of antigen recognition by antibodies in immune sera and in fractions obtained after protein A chromatography of immune sera were investigated by western blotting and immunostaining. Antibodies from AKR(H‐2K) and CBA/H (H‐2k) mice reacted strongly after immunoblotting with antigens of 87 and 96 kDa. In contrast, immune sera from both the highly susceptible DBA/2J (H‐2d) mice and the resistant BALB/c (H‐2d) mice reacted strongly with an antigen of 48 kDa. C57BI/6J (H‐2b) mice produced variable antibody reactivity to antigens of 48, 65, 66 and 79 kDa depending on the IgG subclass tested. The IgG subclass responses and the patterns of antigen recognition in these mice suggest that humoral responses to C albicans may be restricted by H‐2 haplotype. There was no clear correlation between humoral immunity and resistance or susceptibility to infection with C. albicans.
Ultraviolet B irradiation of skin induces mast cell degranulation and release of tumour necrosis factor‐α
Authors: WALSH LAURENCE J
Published: July 2007

In the ‘sunburn’ response in skin, dermal blood vessels are activated and traffic of dendritic Langerhans' cells altered. While these changes have been attributed to the cytokine TNF‐α, the source of this acutely released TNF has not been identified. This report demonstrates that the ‘sunburn’ response, both in vivo and in vitro, is accompanied by rapid degranulation of cutaneous mast cells, with consequential release of intracellular stores of TNF. Epidermal keratinocytes were only minor contributors to local TNF production. Expression of the TNF‐inducible CD62E (E‐selectin/ELAM‐1) and CD54 adhesion molecules on cutaneous endothelium occurred 2 h following mast cell degranulation, and this event was sensitive to blockade of mast cells with disodium cromoglycate. These results indicate that TNF release in skin in the acute sunburn response can largely be attributed to mast cells.
Increased level of activated γδ lymphocytes correlates with disease severity in HIV infection
Authors: NORAZMI MOHD‐NOR , ARIFIN HARUN , JAMARUDDIN MAT ASAN
Published: July 2007

The lymphocyte subset expressing the γδ T cell receptor is increased in several infectious diseases including HIV infection. In this study the expression on γδ lymphoctyes of the T cell activation markers CD25, HLA‐DR and CD38, as well as the two isoforms of CD45, namely CD45RA and CD45RO, was determined in the peripheral blood of 56 HIV‐infected intravenous drug users and 34 HIV‐seronegative blood donors by two‐colour flow cytometry. The percentage of γδ lymphocytes expressing HLA‐DR and CD38 was higher than those in HIV‐seronegative controls (P < 0.001 and P < 0.0001, respectively). Furthermore the HLA‐DR+γδ+ lymphocytes correlated inversely with CD4+ T lymphocyte absolute count (P < 0.02 for both). The levels of γδ lymphocytes expressing CD25, CD45RA and CD45RO were similar to those in HIV‐seronegative controls. Activated γδ lymphocytes may play a role in the HIV disease process and could provide a useful marker for disease progression.
T cell receptor usage in autoimmune disease
Authors: OLIVE COLLEEN
Published: July 2007

Activated T‐cells are believed to play a critical role in the pathogenesis of autoimmune disease. In experimental allergic encephalomyelitis (EAE), an animal model resembling human multiple sclerosis (MS), there is evidence that T cells reactive to myelin basic protein mediate an inflammatory response within the central nervous system leading to demyelination. Furthermore, encephalitogenic T cells express TCR with highly restricted V gene usage and consequently specific forms of immunotherapy directed against V gene products have been successful in preventing and treating EAE. These findings prompted studies into the analysis of TCR repertoire expression in human autoimmune diseases in an attempt to identify the TCR usage of autoreactive and potentially pathogenic T cells. However, this has proved difficult as the autoantigens that drive the T cell response in most human autoimmune disorders are unknown. This review examines the data that have accumulated over the past few years on TCR usage in human autoimmune diseases and is focused largely on rheumatoid arthritis and MS.
Assessment of the therapeutic potential of cytokines, cytotoxic drugs and effector cell populations for the treatment of multiple myeloma using the 5T33 murine myeloma model
Authors: MANNING LINDA S , CHAMBERLAIN NARELLE L , LEAHY MICHAEL F , CORDINGLEY FRANK T
Published: July 2007

The therapeutic potential of six cytokines, eight cytotoxic drugs and two effector cell populations for the treatment of multiple myeloma was assessed in vitro using the 5T33 murine myeloma model. The efficacy of combination IFN‐α and melphalan therapy was also evaluated in vitro and in vivo. Of the cytokines tested in vitro using the MTT assay, only IFN‐α demonstrated significant inhibition of myeloma cell growth at non‐toxic concentrations (ED50= 1508.3 ± 181.3 U/mL and 2617.9 ± 334.0 U/mL for murine IFN‐α [mIFN‐α] and human IFN‐α hybrid B/D [hlFN‐α B/D], respectively). The ED50 for the eight cytotoxic drugs tested ranged from 2.3 × 10−9 to 4.3 × 10−13 mol/L and all were within the therapeutic range for humans. Combination hIFN‐α B/D and melphalan were found to be additive in their inhibitory effects on myeloma cell growth in vitro and this finding was confirmed in vivo in C57BL/KaLwRij mice bearing disseminated 5T33 myeloma. Control animals demonstrated a median survival duration of 25.3 days whereas hIFN‐α B/D or melphalan treatment alone increased survival to 30.5 and 33.3 days, respectively (P < 0.001). Combination IFN‐α/melphalan therapy increased median survival duration to 38.5 days (P < 0.001) which was also significantly greater than that obtained with single agent therapy (P < 0.01). The murine myeloma cells were found to be resistant to NK cell lysis but susceptible to lysis by LAK cells (49.3 ± 6.3% lysis at an effector to target ratio of 100:1). LAK cell precursors were demonstrable in the bone marrow and spleen of tumour‐bearing animals throughout tumour progression. The results of this study suggest that the use of combination immunotherapy/chemotherapy may be more effective than standard chemotherapy alone for the treatment of multiple myeloma.
The 65 kDa protein of Mycobacterium habana and its putative role in immunity against experimental tuberculosis
Authors: SINGH NB , SRIVASTAVA KANCHAN , MALAVIYA B , KANDPAL HEMA , SRIVASTAVA ANIL , GUPTA HP
Published: July 2007

Mycobacteria including Mycobacterium tuberculosis and Mycobacterium leprae possess multiple antigens some of which inhibit other anti‐mycobacterial immune responses. Whole cell vaccines are not free from these suppressive molecules and may adversely affect the immunogenic response(s). Purified protein components having only immunogenic properties should prove to be superior vaccine(s). Mycobacterium habana, a candidate vaccine for mycobacterial infections has been dissected for analysing its antigenic myriad. A 65 kDa protein of this mycobacterium has been isolated and characterized for its protective and cell mediated immune responses. The protein was isolated in pure form using an isotachophoresis (SDS–PAGE filtration) technique and identified with low molecular weight markers along with mAb using the immunoblot technique. Mab IIH9 has identified a 65 kDa protein in M. habana. This protein has been found to be immunoprotective in mice against M. tuberculosis H37Rv infection. It generates high levels of DTH responses in mice against M. tuberculosis and M. leprae antigens and inhibits migration of sensitized cells under the antigenic influence of homologous and heterologous origin. Possibilities of developing this protein as a subunit vaccine are discussed in this report.
The biology of airway dendritic cells
Authors: McWILLIAM ANDREW S , NELSON DELIA J , HOLT PATRICK G
Published: July 2007

Recent work from our laboratory has identified a network of constitutively class II MHC (Ia) bearing dendritic cells (DC) within the epithelium of the conducting airways of laboratory animal species and in humans. The density of DC within the respiratory tract is highest in those areas exposed to greater amounts of inhaled antigen and further work has identified these DC as being critically important in controlling the induction of immune responses within the airways. The DC population in the airway epithelium is renewed every 48–72 h; this represents a more rapid turnover than DC in other tissues which are exposed to a smaller antigenic load. In addition to these results we will discuss other work which shows that airway DC are a very reactive population, comparable with neutrophils in their response to acute inflammatory stimuli and that their numbers and Ia content can be modulated following exposure to topical and systemic steroids. Finally we will discuss the development of these cells after birth and how this may influence the pathogenesis of immune regulated diseases such as asthma and allergic rhinitis.
Lack of serological specificity of recombinant heat shock protein of Leishmania donovani
Authors: ARORA SUNIL K , MELBY PETER C , SEHGAL SHOBHA
Published: July 2007

In order to identify a specific recombinant antigen of Leishmania donovani with potential use for diagnosis, a cDNA library was constructed in lambda ZAP II expression vector. On screening the cDNA library using pooled sera from Indian patients with kala azar, 20 antibody reactive clones were identified. These were subcloned into pBluescript phagemid by an in vivo excision procedure. The molecular weights of the expressed recombinant proteins varied from 15 to 70 kDa and the cDNA insert sizes varied from 0.5 kb to the largest size of approximately 2.0 kb which was designated as the E2b clone. The nucleotide sequencing revealed that 50% of the clones had sequence homology to the heat shock protein gene of L. donovani. The serological studies conducted with the kala azar positive sera and sera from healthy laboratory workers using the recombinant protein from the E2b clone and having sequence homology to Ldhsp 70, indicated that although all the kala azar sera were positive, 12 of 20 healthy individuals also showed antibodies against the recombinant hsp70, indicating that this antigen is not suitable for serological diagnosis of kala azar.
Interleukin‐4 inhibits the expression of tumour necrosis factors α and β, interleukins‐1 β and ‐6 and interferon‐γ
Authors: LEE JEFFREY D. , RHOADES KRISTINA , ECONOMOU JAMES S.
Published: July 2007

T cell‐derived IL‐4 inhibits the expression of several inflammatory cytokine genes. In this study, IL‐4 downregulated TNF‐α and ‐β. IL‐1 β IL‐6 and IFN‐γ steady‐state mRNA and protein production by blood leucocytes. In a detailed kinetic analysis, cytokine mRNA levels were significantly decreased in the presence of IL‐4, suggesting an early and prolonged down regulatory effect. These findings support the general thesis that IL‐4 is an important regulator of the inflammatory immune response.
Data integration in myGrid with Taverna
Authors: Hull Duncan
Published: July 2007

Many areas of life sciences research involve integrating terabytes of heterogeneous, distributed and autonomous data available on the Web. The myGrid project has addressed these challenging problems by developing and applying novel grid and semantic web services technology to life science data integration, particularly genome annotation and microarray analysis. This presentation outlines the past, present and future of the Taverna workflow system.
H
3
+
as a trap for noble gases - 2: structure and energetics of XH3+ complexes from X=neon to xenon
Authors: Pauzat F. , Ellinger Y.
Published: July 2007

The affinity of H3+ to combine with noble gases X has been investigated from neon to xenon using ab initio coupled cluster [CCSD and CCSD(T)] and density functional BH&HLYP levels of theory. For all noble gases, the stable structures belong to a C2v symmetry with an apex of the H3+ triangle pointing to the noble gas. The structure of the complexes changes gradually from a practically pure Ne–H3+ arrangement to a situation close to XeH+–H2. A topological analysis of the electron localization function is used to illustrate the changes in the bonding along the series. The lowest dissociation energies of NeH3+ and ArH3+ (∼1 and ∼7kcal∕mol) correspond to the breaking of the complexes according to X+H3+, while the lowest dissociation energies of KrH3+ and XeH3+ (∼8 and ∼3kcal∕mol) correspond to the breaking according to XH++H2. Rotational constants and harmonic frequencies are reported. Apart from XeH3+ whose dipole moment (μ=2.6D) may not be large enough, all the other complexes with dipole moments in the range of 6–8D should be reasonable targets for detection by microwave spectroscopy. The present calculations are intended to stimulate both laboratory experiments and spatial observations since the possible sequestration of noble gases by H3+ may have strong implications on the composition of astrophysical objects.
Polymers in an external periodic field: The effect of the excluded volume interactions
Authors: Chervanyov A. I. , Heinrich G.
Published: July 2007

By developing and making use of the “transfer operator” formalism, we calculate the number density and average Flory end-to-end distance of the polymers placed in an external periodic field. The considered mathematical problem is of immediate relevance for such realistic physical systems as the homopolymers immersed in the host structure of alternating layers that have different affinities for homopolymers (e.g., lamellar microphases of copolymers, ripple morphology of the mixed brush, and lipid∕water systems). In contrast to the conventional ground state dominance approximation, the developed method makes it possible to calculate the characteristic size (Flory radius RF) of the polymers in the direction of applied external periodic field, with the effect of the excluded volume taken into account. The excluded volume interactions are shown to qualitatively change the behavior of RF as a function of the reduced field strength θ relative to the case of ideal Gaussian polymers. In particular, in the limit of strong fields θ⪢1 the average Flory radius RF is found to saturate to its minimal value, which is calculated as a function of the excluded volume parameter u. This finding is in distinct contrast to the result for the Flory radius RF in the case of ideal polymers where RF approaches zero as the interaction parameter θ increases.
Stabilization of periodically poled domain structures in a quasiphase-matching device using near-stoichiometric
LiTaO
3
Authors: Liu Xiaoyan , Kitamura Kenji , Terabe Kazuya , Takekawa Shunji
Published: July 2007

The stability of periodically poled domain structures in near-stoichiometric lithium tantalite, LiTaO3, (SLT) crystals exhibiting a low coercive field has become an important issue in the use of quasiphase-matching (QPM) devices. Temperature-induced backswitching in inverted domain structures in a 1.0 mol % MgO-doped SLT-QPM device with a QPM period of 6.1 μm used for the second harmonic generation of 488-nm-wavelength light was investigated using scanning force microscopy. It was revealed that backswitching consistently occurred due to heat treatment and that the amount was dependent on the temperature history. We propose an effective method of suppressing backswitching in the inverted domain structures of SLT-QPM devices on the basis of systematically analyzing the backswitching phenomena.
Microwave photoconductivity decay characterization of high-purity 4H-SiC substrates
Authors: Kumar R. J. , Borrego J. M. , Gutmann R. J. , Jenny J. R. , Malta D. P. , Hobgood H. McD. , Carter C. H.
Published: July 2007

A microwave photoconductivity decay (MPCD) technique, which probes conductivity change in wafers in response to either an above-band-gap or below-band-gap laser pulse, has been used to characterize recombination lifetime in high-purity 4H-SiC substrates produced with three different anneal processes. The above-band-gap (266nm) decay times vary from ∼10ns to tens of microseconds in the 4H-SiC substrates depending on the wafer growth parameters. Wafers produced using the three processes A (as-grown), B (annealed at 2000°C), and C (annealed at 2600°C) have decay times of 10–20ns, 50–500ns, and tens of microseconds, respectively. The differences in decay times are attributed to low, medium, and high densities of recombination centers in process C, B, and A wafers, respectively. The MPCD results correlate with other characterization results such as deep level transient spectroscopy, which also showed that the 2600°C anneal process significantly reduces defect densities, resulting in the enhanced recombination lifetimes. Modeling and one-dimensional simulations indicate a trapping center closer to the conduction band results in a longer MPCD decay transient, but such a trapping based model for the enhanced lifetimes is not compatible with the wide range of experimental characterization results described in this work, which indicate an annealing out of recombination centers at 2600°C.
Modeling boundary conditions for computation of piezoelectric fields in quantum dots with image charge analogy
Authors: Melezhik Evgen O. , Korotchenkov O. A.
Published: July 2007

We present a simple approach for calculating the piezoelectric fields exerted by a stressor quantum dot buried in a semi-infinite piezoelectric matrix with a weak electromechanical coupling factor. It aims to take into account the electrical boundary conditions by introducing an image quantum dot mirrored the original dot with respect to the matrix surface. The technique is applied to a spherical InAs dot embedded in the GaAs semi-infinite matrix and the computation results exhibit an excellent agreement with more rigorous calculations reported by Pan [E. Pan, J. Appl. Phys. 91, 3785 (2002)]. We demonstrate that the approach can also be used in computing the piezoelectric fields for a square pyramid embedded in a semi-infinite matrix. It is furthermore anticipated that application of the method can remarkably simplify calculations of piezoelectric fields generated by arrays of the quantum dots of various shapes grown in a matrix material. These fields are known to be of considerable importance in quantum dot devices.
Contrast enhancement in double-layered dye-doped polymer-dispersed liquid-crystal cells
Authors: Scherschener Elizabeth , Dalchiele Enrique A. , Frins Erna M. , Perciante César D. , Ferrari José A.
Published: July 2007

In this article, the light transmission process in single- and double-layered polymer-dispersed liquid-crystal (PDLC) cells and its relevance for contrast ratio calculations have been discussed. Double-layered cells consist of two PDLC films with a common central wall. We demonstrate theoretically and experimentally that the contrast ratio of double-layered cells is larger than the one of a single PDLC film, but in general, it is not the product of the contrast ratios of the individual films, contrary to the result obtained neglecting multiple scattered light. The same result holds for a single film working in reflective mode. Our results may be potentially relevant for display applications.
Suppression of silicidation and crystallization by atmosphere controlled annealing for poly-crystalline silicon/HfO2∕SiO2∕Si gate stack structures
Authors: Takahashi H. , Toyoda S. , Okabayashi J. , Kumigashira H. , Oshima M. , Ikeda K. , Liu G. L. , Liu Z. , Usuda K.
Published: July 2007

The suppression of silicidation and crystallization of gate dielectrics for polycrystalline-Si∕HfO2∕SiO2∕Si gate sack structures by controlling annealing ambient has been investigated using photoemission and x-ray absorption spectroscopy. It is found that both silicidation and crystallization are suppressed by a mixture gas (nitrogen and oxygen) annealing. Meanwhile, by nitrogen annealing at the same partial pressure, both silicidation and crystallization occur. In the case of oxygen annealing, silicidation does not occur while only crystallization occurs. From these results, it is concluded that nitrogen and oxygen gases play a role of preventing silicidation and crystallization, respectively.
High efficiency InGaAs solar cells on Si by InP layer transfer
Authors: Zahler James M. , Tanabe Katsuaki , Ladous Corinne , Pinnington Tom , Newman Frederick D. , Atwater Harry A.
Published: July 2007

In P ∕ Si substrates were fabricated through wafer bonding and helium-induced exfoliation of InP, and InGaAs solar cells lattice matched to bulk InP were grown on these substrates using metal-organic chemical-vapor deposition. The photovoltaic characteristics of the InGaAs cells fabricated on the wafer-bonded InP∕Si substrates were comparable to those synthesized on commercially available epiready InP substrates, thus providing a demonstration of wafer-bonded InP∕Si substrates as an alternative to bulk InP substrates for solar cell applications.
Low-temperature method for enhancing sputter-deposited HfO2 films with complete oxidization
Authors: Tsai Chih-Tsung , Chang Ting-Chang , Liu Po-Tsun , Yang Po-Yu , Kuo Yu-Chieh , Kin Kon-Tsu , Chang Pei-Lin , Huang Fon-Shan
Published: July 2007

A low-temperature method, supercritical CO2 fluid (SCF) technology, is proposed to improve the dielectric properties of ultrathin hafnium oxide (HfO2) film at 150°C without significant formation of parasitic oxide at the interface between HfO2 and Si substrate. In this research, the HfO2 films were deposited by dc sputter at room temperature and post-treated by SCF which is mixed with 5vol% propyl alcohol and 5vol% H2O. From high-resolution transmission electron microscopy image, the interfacial oxide of SCF-treated HfO2 film is only 5Å thick. Additionally, the enhancements in the qualities of sputter-deposited HfO2 film after SCF process are exhibited by x-ray photoelectron spectroscopy and capacitance-voltage (C-V) measurement.
Differential atomic magnetometry based on a diverging laser beam
Authors: Hodby E. , Donley E. A. , Kitching J.
Published: July 2007

The authors demonstrate a novel atomic magnetometer that uses differential detection of the spatially diverging components of a light field to monitor the Larmor precession frequency of atoms in a thermal vapor. The design is implemented in compact form with a micromachined alkali vapor cell and a naturally divergent light field emitted by a vertical-cavity surface-emitting laser. Operating the magnetometer in differential mode cancels common-mode noise and improves the sensitivity by a factor of 26 over single-channel operation. They also suggest ways in which the current sensitivity of 28pT∕√Hz may be improved further without sacrificing size or simplicity.
Fire scars reveal source of New England's 1780 Dark Day
Authors: McMurry Erin R. , Stambaugh Michael C. , Guyette Richard P. , Dey Daniel C.
Published: July 2007

Historical evidence suggests that great wildfires burning in the Lake States and Canada can affect atmospheric conditions several hundred miles away (Smith 1950; Wexler 1950). Several ‘dark’ or ‘yellow’ days, as such events are commonly called, have been recorded, often with anecdotal or direct evidence pointing to wildfires as the source (Plummer 1912; Ludlum 1972). One such ‘dark day’ occurred across New England in 1780, a year in which people were technologically unable to confirm the source of such a phenomenon. Here we combine written accounts and fire scar evidence to document wildfire as the likely source of the infamous Dark Day of 1780.
Chemotactic action of prostaglandin E2on mouse mast cells acting via the PGE2receptor 3
Authors: Weller Charlotte L. , Collington Sarah J. , Hartnell Adele , Conroy Dolores M. , Kaise Toshihiko , Barker Jane E. , Wilson Mark S. , Taylor Graham W. , Jose Peter J. , Williams Timothy J.
Published: July 2007

Mast cells are long-lived cells that are principally recognized for their effector function in helminth infections and allergic reactions. These cells are derived from pluripotential hematopoietic stem cells in the bone marrow that give rise to committed mast cell progenitors in the blood and are recruited to tissues, where they mature. Little is known about the chemotactic signals responsible for recruitment of progenitors and localization of mature mast cells. A mouse model was set up to identify possible mast cell progenitor chemoattractants produced during repeated allergen challengein vivo. After the final challenge, the nasal mucosa was removed to produce conditioned medium, which was tested in chemotaxis assays against 2-wk murine bone marrow-derived c-kit+mast cells (BMMC). A single peak of chemotactic activity was seen on reverse-phase HPLC with a retention time and electrospray mass spectrum consistent with prostaglandin E2(PGE2).This lipid was found to be a highly potent chemoattractant for immature (2-wk) and also mature (10-wk) BMMCin vitro. Fluorescently labeled 2-wk c-kit+BMMC, when injected intravenously, accumulated in response to intradermally injected PGE2. Analysis using TaqMan showed mRNA expression of the PGE2receptors 3 (EP3) and 4 (EP4) on 2- and 10-wk BMMC. Chemotaxis induced by PGE2was mimicked by EP3 agonists, blocked by an EP3 receptor antagonist, and partially inhibited by a MAPKK inhibitor. These results show an unexpected function for PGE2in the chemotaxis of mast cells.
Crossing the final ecological threshold in high Arctic ponds
Authors: Smol John P. , Douglas Marianne S. V.
Published: July 2007

A characteristic feature of most Arctic regions is the many shallow ponds that dot the landscape. These surface waters are often hotspots of biodiversity and production for microorganisms, plants, and animals in this otherwise extreme terrestrial environment. However, shallow ponds are also especially susceptible to the effects of climatic changes because of their relatively low water volumes and high surface area to depth ratios. Here, we describe our findings that some high Arctic ponds, which paleolimnological data indicate have been permanent water bodies for millennia, are now completely drying during the polar summer. By comparing recent pond water specific conductance values to similar measurements made in the 1980s, we link the disappearance of the ponds to increased evaporation/precipitation ratios, probably associated with climatic warming. The final ecological threshold for these aquatic ecosystems has now been crossed: complete desiccation.
Bak regulates mitochondrial morphology and pathology during apoptosis by interacting with mitofusins
Authors: Brooks Craig , Wei Qingqing , Feng Leping , Dong Guie , Tao Yanmei , Mei Lin , Xie Zi-Jian , Dong Zheng
Published: July 2007

Mitochondrial injury, characterized by outer membrane permeabilization and consequent release of apoptogenic factors, is a key to apoptosis of mammalian cells. Bax and Bak, two multidomain Bcl-2 family proteins, provide a requisite gateway to mitochondrial injury. However it is unclear how Bax and Bak cooperate to provoke mitochondrial injury and whether their roles are redundant. Here, we have identified a unique role of Bak in mitochondrial fragmentation, a seemingly morphological event that contributes to mitochondrial injury during apoptosis. We show that mitochondrial fragmentation is attenuated in Bak-deficient mouse embryonic fibroblasts, baby mouse kidney cells, and, importantly, also in primary neurons isolated from brain cortex of Bak-deficient mice. In sharp contrast, Bax deficiency does not prevent mitochondrial fragmentation during apoptosis. Bcl-2 and Bcl-XL inhibit mitochondrial fragmentation, and their inhibitory effects depend on the presence of Bak. Reconstitution of Bak into Bax/Bak double-knockout cells restores mitochondrial fragmentation, whereas reconstitution of Bax is much less effective. Bak interacts with Mfn1 and Mfn2, two mitochondrial fusion proteins. During apoptosis, Bak dissociates from Mfn2 and enhances the association with Mfn1. Mutation of Bak in the BH3 domain prevents its dissociation from Mfn2 and diminishes its mitochondrial fragmentation activity. This study has uncovered a previously unrecognized function of Bak in the regulation of mitochondrial morphological dynamics during apoptosis. By this function, Bak may collaborate with Bax to permeabilize the outer membrane of mitochondria, unleashing the apoptotic cascade.
Crystal structures of murine thrombin in complex with the extracellular fragments of murine protease-activated receptors PAR3 and PAR4
Authors: Bah Alaji , Chen Zhiwei , Bush-Pelc Leslie A. , Mathews F. Scott , Di Cera Enrico
Published: July 2007

It has been proposed that the cleaved form of protease-activated receptor 3 (PAR3) acts as a cofactor for thrombin cleavage and activation of PAR4 on murine platelets, but the molecular basis of this physiologically important effect remains elusive. X-ray crystal structures of murine thrombin bound to extracellular fragments of the murine receptors PAR3 (
38
SFNGGPQNTFEEFPLSDIE
56
) and PAR4 (
51
KSSDKPNPR ↓ GYPGKFCANDSDTLELPASSQA
81
, ↓ = site of cleavage) have been solved at 2.0 and 3.5 Å resolution, respectively. The cleaved form of PAR3, traced in the electron density maps from Gln-44 to Glu-56, makes extensive hydrophobic and electrostatic contacts with exosite I of thrombin through the fragment
47
FEEFPLSDIE
56
. Occupancy of exosite I by PAR3 allosterically changes the conformation of the 60-loop and shifts the position of Trp-60d ≈10 Å with a resulting widening of the access to the active site. The PAR4 fragment, traced entirely in the electron density maps except for five C-terminal residues, clamps Trp-60d, Tyr-60a, and the aryl-binding site of thrombin with Pro-56 and Pro-58 at the P2 and P4 positions and engages the primary specificity pocket with Arg-59. The fragment then leaves the active site with Gly-60 and folds into a short helical turn that directs the backbone away from exosite I and over the autolysis loop. The structures demonstrate that thrombin activation of PAR4 may occur with exosite I available to bind cofactor molecules, like the cleaved form of PAR3, whose function is to promote substrate diffusion into the active site by allosterically changing the conformation of the 60-loop.
The plant signal salicylic acid shuts down expression of the
vir
regulon and activates quormone-quenching genes in
Agrobacterium
Authors: Yuan Ze-Chun , Edlind Merritt P. , Liu Pu , Saenkham Panatda , Banta Lois M. , Wise Arlene A. , Ronzone Erik , Binns Andrew N. , Kerr Kathleen , Nester Eugene W.
Published: July 2007

Agrobacterium tumefaciens
is capable of transferring and integrating an oncogenic T-DNA (transferred DNA) from its tumor-inducing (Ti) plasmid into dicotyledonous plants. This transfer requires that the virulence genes (
vir
regulon) be induced by plant signals such as acetosyringone in an acidic environment. Salicylic acid (SA) is a key signal molecule in regulating plant defense against pathogens. However, how SA influences
Agrobacterium
and its interactions with plants is poorly understood. Here we show that SA can directly shut down the expression of the
vir
regulon. SA specifically inhibited the expression of the
Agrobacterium virA
/
G
two-component regulatory system that tightly controls the expression of the
vir
regulon including the
repABC
operon on the Ti plasmid. We provide evidence suggesting that SA attenuates the function of the VirA kinase domain. Independent of its effect on the
vir
regulon, SA up-regulated the
attKLM
operon, which functions in degrading the bacterial quormone
N
-acylhomoserine lactone. Plants defective in SA accumulation were more susceptible to
Agrobacterium
infection, whereas plants overproducing SA were relatively recalcitrant to tumor formation. Our results illustrate that SA, besides its well known function in regulating plant defense, can also interfere directly with several aspects of the
Agrobacterium
infection process.
The development of learning to learn in Spain
Authors: Moreno Amparo , Martín Elena
Published: July 2007

In this article, we describe how the concept of ‘learning to learn’ has developed in Spain, and give you an overview of relevant Spanish projects. First, we sketch out how this approach has developed in Spanish educational laws. We then give examples of research projects, assessment instruments and instructional programmes pertinent to each of the four main concepts of learning to learn in Spain—study techniques, learning to reason, learning strategies and metacognitive learning. We also try to focus on the social and emotional aspects of learning to learn. To this end, we discuss cooperative learning, the parent's role in academic self‐regulation, motivation and self‐esteem. We come to the conclusion that the Spanish school system and Spanish research groups are both profoundly interested in learning to learn. Nevertheless, we still find weak points in the results achieved by students and teachers, as well as in the theoretical models and assessment tools. Therefore, we propose some improvements to learning to learn in Spain.
Research into learning to learn through the assessment of quality and organization of learning outcomes
Authors: Csapó Benő
Published: July 2007

This article examines the problem of learning to learn from the perspective of research on the organization and quality of students' knowledge. This approach is based on the assumption that students' learning competencies can be studied through the analysis of the outcomes of schooling. The article synthesizes findings of a long‐term research programme assessing the development of components of propositional and procedural knowledge, and relationships between them. A model was devised classifying indicators of school outcomes on four levels: (1) teachers' grading; (2) objective knowledge tests; (3) indicators of quality of knowledge (application, understanding); and (4) higher order thinking skills. A set of tests and questionnaires were administered to Year 7 and Year 11 students in two consecutive projects; then, relationships between them and differences between the two cohorts were analysed. As results indicate, a number of points in schooling should be changed in order to improve schools' impact on learning to learn, for example, inadequate feedback given by grading, and shifting attention from reproductive to productive learning. The instruments developed in this programme assess science application, science misconception, mathematical understanding, historical reasoning, and inductive, deductive, spatial and critical reasoning. They can also be utilized for monitoring learning to learn.
Role for DNA repair factor XRCC4 in immunoglobulin class switch recombination
Authors: Soulas-Sprauel Pauline , Le Guyader Gwenaël , Rivera-Munoz Paola , Abramowski Vincent , Olivier-Martin Christelle , Goujet-Zalc Cécile , Charneau Pierre , de Villartay Jean-Pierre
Published: July 2007

V(D)J recombination and immunoglobulin class switch recombination (CSR) are two somatic rearrangement mechanisms that proceed through the introduction of double-strand breaks (DSBs) in DNA. Although the DNA repair factor XRCC4 is essential for the resolution of DNA DSB during V(D)J recombination, its role in CSR has not been established. To bypass the embryonic lethality of XRCC4 deletion in mice, we developed a conditional XRCC4 knockout (KO) using LoxP-flanked XRCC4 cDNA lentiviral transgenesis. B lymphocyte restricted deletion of XRCC4 in these mice lead to an average two-fold reduction in CSR in vivo and in vitro. Our results connect XRCC4 and the nonhomologous end joining DNA repair pathway to CSR while reflecting the possible use of an alternative pathway in the repair of CSR DSB in the absence of XRCC4. In addition, this new conditional KO approach should be useful in studying other lethal mutations in mice.
Activation phenotype, rather than central– or effector–memory phenotype, predicts the recall efficacy of memory CD8+ T cells
Authors: Hikono Hirokazu , Kohlmeier Jacob E. , Takamura Shiki , Wittmer Susan T. , Roberts Alan D. , Woodland David L.
Published: July 2007

The contributions of different subsets of memory CD8+ T cells to recall responses at mucosal sites of infection are poorly understood. Here, we analyzed the CD8+ T cell recall responses to respiratory virus infection in mice and demonstrate that activation markers, such as CD27 and CD43, define three distinct subpopulations of memory CD8+ T cells that differ in their capacities to mount recall responses. These subpopulations are distinct from effector– and central–memory subsets, coordinately express other markers associated with activation status, including CXCR3, CD127, and killer cell lectin-like receptor G1, and are superior to CD62L in predicting the capacity of memory T cells to mediate recall responses. Furthermore, the capacity of vaccines to elicit these memory T cell subpopulations predicted the efficacy of the recall response. These findings extend our understanding of how recall responses are generated and suggest that activation and migration markers define distinct, and unrelated, characteristics of memory T cells.
Lewis Dahl and the genetics of salt-induced hypertension
Authors: Bashyam Hema
Published: July 2007

In the 1960s, Lewis Dahl bred two strains of rats that differed in their susceptibility to developing salt-induced hypertension. These animal models proved that hypertension induced by a high-salt diet is influenced by genetic background.