1,720,970 research outputs found
Surfactant protein A (SP-A) binds to phosphatidylserine and competes with annexin V binding on late apoptotic cells
No full textThe role of surfactant protein A (SP-A) in the recognition and clearance of apoptotic cells is well established, but to date, it is still not clear which surface molecules of apoptotic cells are involved in the process. Here we present evidence that phosphatidylserine (PS) is a relevant binding molecule for human SP-A. The binding is Ca2+-dependent and is not inhibited by mannose, suggesting that the sugar-binding site of the carbohydrate recognition domain (CRD) of SP-A is not involved. Flow cytometry studies on apoptotic Jurkat cells revealed apparent inhibition of annexin V binding by increasing concentrations of SP-A in late apoptotic but not early apoptotic cells, and this was consistent for Jurkat cells and neutrophils. Supporting these data, confocal microscopy results show a co-localisation of annexin V and SP-A in late apoptotic but not early apoptotic cells. However, we cannot conclude that this inhibition is exclusively due to the binding of SP-A to PS on the cell surface, as annexin V is not wholly specific for PS and SP-A also interacts with other phospholipids that might become exposed on the apoptotic cell surface. <br/
Innate immune collectin surfactant protein D enhances the clearance of DNA by macrophages and minimizes anti-DNA antibody generation
No full textDying microbes and necrotic cells release highly viscous DNA that induces inflammation and septic shock, and apoptotic cells display DNA, a potential autoantigen, on their surfaces. However, innate immune proteins that mediate the clearance of free DNA and surface DNA-containing cells are not clearly established. Pulmonary surfactant proteins (SP-) A and D are innate immune pattern recognition collectins that contain fibrillar collagen-like regions and globular carbohydrate recognition domains (CRDs). We have recently shown that collectins SP-A, SP-D, and mannose binding lectin recognize DNA and RNA via their collagen-like regions and CRDs. Here we show that SP-D enhances the uptake of Cy3-labeled fragments of DNA and DNA-coated beads by U937 human monocytic cells, in vitro. Analysis of DNA uptake by freshly isolated mouse alveolar macrophages shows that SP-D, but not SP-A, deficiency results in reduced clearance of DNA, ex vivo. Analysis of bronchoalveolar lavage fluid shows that SP-D- but not SP-A-deficient mice are defective in clearing free DNA from the lung. Additionally, both SP-A- and SP-D-deficient mice accumulate anti-DNA Abs in sera in an age-dependent manner. Thus, we conclude that collectins such as SP-A and SP-D reduce the generation of anti-DNA autoantibody, which may be explained in part by the defective clearance of DNA from the lungs in the absence of these proteins. Our findings establish two new roles for these innate immune proteins and that SP-D enhances efficient pinocytosis and phagocytosis of DNA by macrophages and minimizes anti-DNA Ab generation
Structure and activity of factor D̄ of the alternative pathway of human complement
Full text link1. A method for the purification of the serine protease,factor D,was developed using conventional chromatographic procedures. The final product was homogeneous as judged by SDS/polyacrylamide gel electrophoresis, its migration as a single component in ion exchange and gel filtration media, and its amino acid sequence analysis. The molecule had an apparent molecular weiyht of 24,000. It contained <1.5% (w/w) reducing sugars as judged by periodic acid/Schiff staining, and existed as a monomer in buffers containing either EDTA or calcium ions. 2. Approximately 84% of the amino acid sequence was established unequivocally by automated sequence analysis of the intact molecule and peptides derived by digestion with CNBr, o-iodosobenzoic acid, trypsin and V8 protease. Carboxypeptidase-Y digestion was used to establish the C-terminal amino acid. The peptides were aligned either by homology with other serine proteases, or by the overlap of sequences obtained from peptides derived by different fragmentation procedures. The molecule nad a typical serine protease-type sequence with isoleucine as the Nterminal amino acid. The active site serine and aspartic acid and the surrounding sequences were conserved as well as the sequence around the position of the active site histidine, although this residue itself was not identified. 3. The possibility of the existence of a factor D̄ zymogen which can be activated by trypsin was reinvestigated, but no evidence for a precursor was found. No enzymic activity towards a number of p-nitroanilide substrates and arginyl and lysyl esters was observed with factor D̄,but it was found to release p-nitrophenol from p-nitrophenyl-p'-guanidinobenzoate. Factor D̄ was inhibited by diisopropylphosphofluoridate and p-nitrophenyl-p'-guanidinobenzoate, but a variety of other non-protein and protein inhibitors including α2-macroglobulin, c1 inhibitor and inter-α-trypsin inhibitor had no effect on enzymic activity
Collectins and innate immunity in the lung: therapeutic potential of a recombinant fragment of human surfactant protein D in lung disease
No full textThis thesis examines the role played by the lung collectins, surfactant proteins A and D (SP-A and SP-D) in innate immunity in the lung. The generation of SP-A and SP-D deficient mice has confirmed the important part played by these innate immune molecules in the defence of the lung against infection and in the control of inflammation. SP-A deficient mice are susceptible to infection with a range of microbes. The critical role played by SP-D in controlling inflammation in the lung has been convincingly demonstrated in the SP-D deficient mouse which shows a chronic low grade lung inflammation and the spontaneous development of emphysema. The thesis examines the in vivo activity of recombinant forms of surfactant proteins, in particular a recombinant fragment of surfactant protein D, in the control of lung inflammation using SP-D deficient mice as a model of emphysema. Murine models of allergic inflammation to fungal and common house dust mite allergens were employed to assess the efficacy of recombinant collectins in modulating allergic processes in vivo. The animal models employed and the generation and structural characterisation of recombinant SP-Dare described in the first sections of the thesis. SP-A and SP-D are known to bind to fungal aeroallergens and to allergens of the common house dust mite. Therapeutic testing of the recombinant fragment of surfactant protein D was carried out in mouse models of allergy against allergens of the common house dust mite Dermatophagoides pterynossinus and those of the fungus Aspergillus fumigatus. Exogenously administered collectin reduced serum eosinophilia, IgE and specific IgG 1 levels as well as airway hyperresponsiveness to challenge with both fungal and house dust mite allergens. Further characterisation of the lung phenotype of the SP-D deficient mouse and the use of replacement therapy in correcting the phenotype revealed that SP-D deficient mice have an increased burden of apoptotic and necrotic inflammatory cells in the alveolar space. Treatment of these mice with a recombinant fragment of surfactant protein D led to a marked reduction of the number of apoptotic and necrotic alveolar macrophages in the alveolar space and a partial resolution of the inflammation and excess production of surfactant phospholipids. These results indicate the critical role played by SP-D in regulating inflammation in the lung and the efficacy of a recombinant fragment of SP-D in reducing inflammation in the SP-D deficient lung. Finally the results of a pilot investigation into the levels of SP-Din a population of intubated neonates is presented. The clinical implications of the findings of the thesis are discussed in chapter four, focussing on the therapeutic potential of the recombinant fragment of SP-D to reduce inflammation in neonatal chronic lung disease, cystic fibrosis and adult emphysema
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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