18 research outputs found
Coagulation systems of invertebrates and vertebrates and their roles in innate immunity: The same side of two coins?
No full textTorsten G. Loof, Otto Schmidt, Heiko Herwald, Ulrich Theopol
by Dendritic Cells
No full textStreptococcus pyogenes is one of the most frequent human pathogens. Recent studies have identified dendritic cells (DCs) as important contributors to host defense against S. pyogenes. The objective of this study was to identify the receptors involved in immune recognition of S. pyogenes by DCs. To determine whether Toll-like receptors (TLRs) were involved in DC sensing of S. pyogenes, we evaluated the response of bone marrow-derived DCs obtained from mice deficient in MyD88, an adapter molecule used by almost all TLRs, following S. pyogenes stimulation. Despite the fact that MyD88(-/-) DCs did not differ from wild-type DCs in the ability to internalize and kill S. pyogenes, the up-regulation of maturation markers, such as CD40, CD80, and CD86, and the production of inflammatory cytokines, such as interleukin-12 (IL-12), IL-6, and tumor necrosis factor alpha, were dramatically impaired in S. pyogenes-stimulated MyD88(-/-) DCs. These results suggest that signaling through TLRs is the principal pathway by which DCs sense S. pyogenes and become activated. Surprisingly, DCs deficient in signaling through each of the TLRs reported as potential receptors for gram-positive cell components, such as TLR1, TLR2, TLR4, TLR9, and TLR2/6, were not impaired in the secretion of proinflammatory cytokines and the up-regulation of costimulatory molecules after S. pyogenes stimulation. In conclusion, our results exclude a major involvement of a single TLR or the heterodimer TLR2/6 in S. pyogenes sensing by DCs and argue for a multimodal recognition in which a combination of several different TLR-mediated signals is essential for a rapid and effective response to the pathogen
The role of coagulation/fibrinolysis during Streptococcus pyogenes infection
No full textThe hemostatic system comprises platelet aggregation, coagulation and fibrinolysis and is a host defense mechanism that protects the integrity of the vascular system after tissue injury. During bacterial infections, the coagulation system cooperates with the inflammatory system to eliminate the invading pathogens. However, pathogenic bacteria have frequently evolved mechanisms to exploit the hemostatic system components for their own benefit. Streptococcus pyogenes, also known as Group A Streptococcus, provides a remarkable example of the extraordinary capacity of pathogens to exploit the host hemostatic system to support microbial survival and dissemination. The coagulation cascade comprises the contact system (also known as the intrinsic pathway) and the tissue factor pathway (also known as the extrinsic pathway), both leading to fibrin formation. During the early phase of S. pyogenes infection, the activation of the contact system eventually leads to bacterial entrapment within a fibrin clot, where S. pyogenes is immobilized and killed. However, entrapped S. pyogenes can circumvent the antimicrobial effect of the clot by sequestering host plasminogen on the bacterial cell surface that, after conversion into its active proteolytic form, plasmin, degrades the fibrin network and facilitates the liberation of S. pyogenes from the clot. Furthermore, the surface-localized fibrinolytic activity also cleaves a variety of extracellular matrix proteins, thereby enabling S. pyogenes to migrate across barriers and disseminate within the host. This review summarizes the knowledge gained during the last two decades on the role of coagulation/fibrinolysis in host defense against S. pyogenes as well as the strategies developed by this pathogen to evade and exploit these host mechanisms for its own benefit
Aberrant Inflammatory Response to Streptococcus pyogenes in Mice Lacking Myeloid Differentiation Factor 88.
No full textSeveral in vitro studies have emphasized the importance of toll-like receptor/myeloid differentiation factor 88 (MyD88) signaling in the inflammatory response to Streptococcus pyogenes. Since the extent of inflammation has been implicated in the severity of streptococcal diseases, we have examined here the role of toll-like receptor/MyD88 signaling in the pathophysiology of experimental S. pyogenes infection. To this end, we compared the response of MyD88-knockout (MyD88(-/-)) after subcutaneous inoculation with S. pyogenes with that of C57BL/6 mice. Our results show that MyD88(-/-) mice harbored significantly more bacteria in the organs and succumbed to infection much earlier than C57BL/6 animals. Absence of MyD88 resulted in diminished production of inflammatory cytokines such as interleukin-12, interferon-gamma, and tumor necrosis factor-alpha as well as chemoattractants such as monocyte chemotactic protein-1 (MCP-1) and Keratinocyte-derived chemokine (KC), and hampered recruitment of effector cells involved in bacterial clearance (macrophages and neutrophils) to the infection site. Furthermore, MyD88(-/-) but not C57BL/6 mice exhibited a massive infiltration of eosinophils in infected organs, which can be explained by an impaired production of the regulatory chemokines, gamma interferon-induced monokine (MIG/CXCL9) and interferon-induced protein 10 (IP-10/CXCL10), which can inhibit transmigration of eosinophils. Our results indicate that MyD88 signaling targets effector cells to the site of streptococcal infection and prevents extravasation of cells that can induce tissue damage. Therefore, MyD88 signaling may be important for shaping the quality of the inflammatory response elicited during infection to ensure optimal effector functions
Improved innate and adaptive immunostimulation by genetically modified HIV-1 protein expressing NYVAC vectors.
No full textAttenuated poxviruses are safe and capable of expressing foreign antigens. Poxviruses are applied in veterinary vaccination and explored as candidate vaccines for humans. However, poxviruses express multiple genes encoding proteins that interfere with components of the innate and adaptive immune response. This manuscript describes two strategies aimed to improve the immunogenicity of the highly attenuated, host-range restricted poxvirus NYVAC: deletion of the viral gene encoding type-I interferon-binding protein and development of attenuated replication-competent NYVAC. We evaluated these newly generated NYVAC mutants, encoding HIV-1 env, gag, pol and nef, for their ability to stimulate HIV-specific CD8 T-cell responses in vitro from blood mononuclear cells of HIV-infected subjects. The new vectors were evaluated and compared to the parental NYVAC vector in dendritic cells (DCs), RNA expression arrays, HIV gag expression and cross-presentation assays in vitro. Deletion of type-I interferon-binding protein enhanced expression of interferon and interferon-induced genes in DCs, and increased maturation of infected DCs. Restoration of replication competence induced activation of pathways involving antigen processing and presentation. Also, replication-competent NYVAC showed increased Gag expression in infected cells, permitting enhanced cross-presentation to HIV-specific CD8 T cells and proliferation of HIV-specific memory CD8 T-cells in vitro. The recombinant NYVAC combining both modifications induced interferon-induced genes and genes involved in antigen processing and presentation, as well as increased Gag expression. This combined replication-competent NYVAC is a promising candidate for the next generation of HIV vaccines
Rapport van de Commissie voor het onderzoek naar de spanningstoestand in dijken
No full textDit onderzoek was begonnen met het vaststellen van de toestand, waarin de dijken zich na de ramp bevonden. Een zeer uitvoerige documentatie, in de vorm van fotografische opnamen van dijkbeschadigingen en beschrijvingen van resultaten van profielonderzoekingen. De werkzaamheden der Commissie kunnen, al naar gelang van het gekozen uitgangspunt, worden verdeeld in drie groepen: A. De analyse van waargenomen verschijnselen bij de beschadiging en de doorbraak van bestaande dijken, waarbij in hoofdzaak correlaties tussen uitwendige factoren, de kwaliteit van de dijk en de mate van beschadiging werden bepaald. B. De analyse van elastische spanningstoestanden, welke bij een veronderstelde geometrie van het dijkslichaam kunnen voorkomen, mede in verband met de samenhang en de vervormingseigenschappen van het materiaal. C. De analyse van grenstoestanden van het inwendig evenwicht, welke bij een veronderstelde geometrie van het dijkslichaam en wrijvingseigenschappen van het dijksmateriaal, door uit- en inwendige belastingtoestanden kunnen worden veroorzaakt
Coagulation, an ancestral serine protease cascade, exerts a novel function in early immune defense.
No full textPhylogenetically conserved serine protease cascades play an important role in invertebrate and vertebrate immunity. The mammalian coagulation system can be traced back some 400 million years and it shares homology with ancestral serine proteinase cascades involved for instance in Toll receptor signaling in insects and release of antimicrobial peptides during hemolymph clotting. Here we show that bacteria-evoked induction of coagulation leads to an immobilization and killing of Streptococcus pyogenes bacteria inside the clot. The entrapment is mediated via crosslinking bacteria to fibrin fibers by the action of coagulation factor XIII (fXIII), an evolutionarily conserved transglutaminase. In a streptococcal skin infection model, fXIII(-/-) mice develop severe signs of pathologic inflammation at the local site of infection and fXIII-treatment of wildtype animals dampens bacterial dissemination during early infection. Bacterial killing and crosslinking to fibrin networks was also detected in tissue biopsies from patients with streptococcal necrotizing fasciitis supporting the concept that coagulation is part of the early innate immune system
Linoleic and palmitoleic acid block streptokinase-mediated plasminogen activation and reduce severity of invasive group A streptococcal infection
No full textIn contrast to mild infections of Group A Streptococcus (GAS) invasive infections of GAS still pose a serious health hazard: GAS disseminates from sterile sites into the blood stream or deep tissues and causes sepsis or necrotizing fasciitis. In this case antibiotics do not provide an effective cure as the bacteria are capable to hide from them very quickly. Therefore, new remedies are urgently needed. Starting from a myxobacterial natural products screening campaign, we identified two fatty acids isolated from myxobacteria, linoleic and palmitoleic acid, specifically blocking streptokinase-mediated activation of plasminogen and thereby preventing streptococci from hijacking the host's plasminogen/plasmin system. This activity is not inherited by other fatty acids such as oleic acid and is not attributable to the killing of streptococci. Moreover, both fatty acids are superior in their inhibitory properties compared to two clinically used drugs (tranexamic or ϵ-amino caproic acid) as they show 500-1000 fold lower IC values. Using a humanized plasminogen mouse model mimicking the clinical situation of a local GAS infection that becomes systemic, we demonstrate that these fatty acids ameliorate invasive GAS infection significantly. Consequently, linoleic and palmitoleic acid are possible new options to combat GAS invasive diseases
Pathogen Entrapment by Transglutaminase-A Conserved Early Innate Immune Mechanism
No full textClotting systems are required in almost all animals to prevent loss of body fluids after injury. Here, we show that despite the risks associated with its systemic activation, clotting is a hitherto little appreciated branch of the immune system. We compared clotting of human blood and insect hemolymph to study the best-conserved component of clotting systems, namely the Drosophila enzyme transglutaminase and its vertebrate homologue Factor XIIIa. Using labelled artificial substrates we observe that transglutaminase activity from both Drosophila hemolymph and human blood accumulates on microbial surfaces, leading to their sequestration into the clot. Using both a human and a natural insect pathogen we provide functional proof for an immune function for transglutaminase (TG). Drosophila larvae with reduced TG levels show increased mortality after septic injury. The same larvae are also more susceptible to a natural infection involving entomopathogenic nematodes and their symbiotic bacteria while neither phagocytosis, phenoloxidase or-as previously shown-the Toll or imd pathway contribute to immunity. These results firmly establish the hemolymph/blood clot as an important effector of early innate immunity, which helps to prevent septic infections. These findings will help to guide further strategies to reduce the damaging effects of clotting and enhance its beneficial contribution to immune reactions
An introduction to the applicability of qualitative research methodologies to the field of Library and Information Sciences
No full textThis is the original pre-print written on the 17 November 2003 which eventually got published in 2006 –see its history of publication inside the actual document--, and since the article got originally reduced by the editors of Liber of the Mexican Association of Librarians then this original pre-print includes many examples excluded there by Liber's editors. This is an introductory work to the qualitative research methodologies and methods aplied to the Library and Information Studies (LIS) field, as a way to expand the horizons of librarians so they might be able to explore different roads to improve the common telology of LIS which is basically to fuse the library (informational - cognitive) services with the needs and issues, wishes and dreams of society in its respective communities. It argues for the demystification of LIS research which is impregnated with an halo and cult almost mystical that far from motivating librarians both practical and teorethical to carry out research work in a daily basis, it plays an inhibitor role affecting not only the development of LIS research, but the LIS profession itself; this demystification implies that research could be for everyone who wants it to. It also argues that it is necessary to study in depth the epistemological debate in LIS to promote LIS research as a sub-discipline and the education and training of LIS researchers in order to transform such a plausible activity into an attractive one that becomes even a fun thing to do. The author considers that the examples of applicabilities of qualitative research in LIS given here, but which they could not be included in the published version due to the barriers impossed by the editors of Liber the journal of the Mexican Association of Librarians, are worthwhile to be known by the community interested in these methodologies and it is for them that this original draft is open to the public, thanks to the request of a colleague.
This draft, after many unexplained acts of negligence and censorship by the Chairs of the Mexican Association of Librarians and the other editors of their association journal Liber, during the period of 2004-2005, finally was partly published by this Peruvian journal:
Muela-Meza, Zapopan Martín (2006) Una introducción a las metodologías de investigación cualitativa aplicadas a la bibliotecología. BiblioDocencia : Revista de Profesores de Bibliotecología 2(12):pp. 4-12.
http://eprints.rclis.org/archive/00006732
