The role of released ATP in killing Candida albicans and other extracellular microbial pathogens by cationic peptides

A unifying theme common to the action of many cationic peptides that display lethal activities against microbial pathogens is their specific action at microbial membranes that results in selective loss of ions and small nucleotides chiefly ATP. One model cationic peptide that induces non-lytic release of ATP from the fungal pathogen Candida albicans is salivary histatin 5 (Hst 5). The major characteristic of Hst 5-induced ATP release is that it occurs rapidly while cells are still metabolically active and have polarized membranes, thus precluding cell lysis as the means of release of ATP. Other cationic peptides that induce selective release of ATP from target microbes are lactoferricin, human neutrophil defensins, bactenecin, and cathelicidin peptides. The role of released extracellular ATP induced by cationic peptides is not known, but localized increases in extracellular ATP concentration may serve to potentiate cell killing, facilitate further peptide uptake, or function as an additional signal to activate the host innate immune system at the site of infection

A Novel Role for the NLRC4 Inflammasome in Mucosal Defenses against the Fungal Pathogen Candida albicans

Candida sp. are opportunistic fungal pathogens that colonize the skin and oral cavity and, when overgrown under permissive conditions, cause inflammation and disease. Previously, we identified a central role for the NLRP3 inflammasome in regulating IL-1β production and resistance to dissemination from oral infection with Candida albicans. Here we show that mucosal expression of NLRP3 and NLRC4 is induced by Candida infection, and up-regulation of these molecules is impaired in NLRP3 and NLRC4 deficient mice. Additionally, we reveal a role for the NLRC4 inflammasome in anti-fungal defenses. NLRC4 is important for control of mucosal Candida infection and impacts inflammatory cell recruitment to infected tissues, as well as protects against systemic dissemination of infection. Deficiency in either NLRC4 or NLRP3 results in severely attenuated pro-inflammatory and antimicrobial peptide responses in the oral cavity. Using bone marrow chimeric mouse models, we show that, in contrast to NLRP3 which limits the severity of infection when present in either the hematopoietic or stromal compartments, NLRC4 plays an important role in limiting mucosal candidiasis when functioning at the level of the mucosal stroma. Collectively, these studies reveal the tissue specific roles of the NLRP3 and NLRC4 inflammasome in innate immune responses against mucosal Candida infection

IL-1β Processing in Host Defense: Beyond the Inflammasomes

Stimulation and release of proinflammatory cytokines is an essential step for the activation of an effective innate host defense, and subsequently for the modulation of adaptive immune responses. Interleukin-1β (IL-1β) and IL-18 are important proinflammatory cytokines that on the one hand activate monocytes, macropages, and neutrophils, and on the other hand induce Th1 and Th17 adaptive cellular responses. They are secreted as inactive precursors, and the processing of pro-IL-1β and pro-IL-18 depends on cleavage by proteases. One of the most important of these enzymes is caspase-1, which in turn is activated by several protein platforms called the inflammasomes. Inflammasome activation differs in various cell types, and knock-out mice defective in either caspase-1 or inflammasome components have an increased susceptibility to several types of infections. However, in other infections and in models of sterile inflammation, caspase-1 seems to be less important, and alternative mechanisms such as neutrophil-derived serine proteases or proteases released from microbial pathogens can process and activate IL-1β. In conclusion, IL-1β/IL-18 processing during infection is a complex process in which the inflammasomes are only one of several activation mechanisms

P2 purinergic receptor modulation of cytokine production

Cytokines serve important functions in controlling host immunity. Cells involved in the synthesis of these polypeptide mediators have evolved highly regulated processes to ensure that production is carefully balanced. In inflammatory and immune disorders, however, mis-regulation of the production and/or activity of cytokines is recognized as a major contributor to the disease process, and therapeutics that target individual cytokines are providing very effective treatment options in the clinic. Leukocytes are the principle producers of a number of key cytokines, and these cells also express numerous members of the purinergic P2 receptor family. Studies in several cellular systems have provided evidence that P2 receptor modulation can affect cytokine production, and mechanistic features of this regulation have emerged. This review highlights three separate examples corresponding to (1) P2Y6 receptor mediated impact on interleukin (IL)-8 production, (2) P2Y11 receptor-mediated affects on IL-12/23 output, and (3) P2X7 receptor mediated IL-1β posttranslational processing. These examples demonstrate important roles of purinergic receptors in the modulation of cytokine production. Extension of these cellular observations to in vivo situations may lead to new therapeutic strategies for treating cytokine-mediated diseases

Human cathelicidin production by the cervix

hCAP18/LL-37 is the sole human cathelicidin; a family of host defence peptides with key roles in innate host defence. hCAP18/LL-37 is expressed primarily by neutrophils and epithelial cells, but its production and function in the lower genital tract is largely uncharacterised. Despite the significant roles for cathelicidin in multiple organs and inflammatory processes, its impact on infections that could compromise fertility and pregnancy is unknown. The aim of this study was to investigate cathelicidin production, regulation and function in the cervix. hCAP18/LL-37 was found to be present in cervicovaginal secretions collected from women in the first trimester of pregnancy and to be expressed at significantly higher levels in samples from women with alterations in vaginal bacterial flora characteristic of bacterial vaginosis. In endocervical epithelial cell lines, expression of the gene encoding hCAP18/LL-37 (CAMP) was not affected by TLR agonists, but was found to be up-regulated by both 1, 25 hydroxyvitamin D3 and 25 hydroxyvitamin D3. However, no association was found between serum levels of vitamin D and hCAP18/LL-37 concentrations in cervicovaginal secretions (n = 116). Exposure to synthetic LL-37 had a pro-inflammatory effect on endocervical epithelial cell lines, increasing secretion of inflammatory cytokine IL-8. Together these data demonstrate inducible expression of hCAP18/LL-37 in the female lower reproductive tract in vivo and suggest the capacity for this peptide to modulate host defence to infection in this system. Further investigation will elucidate the effects of hCAP18/LL-37 on the physiology and pathophysiology of labour, and may lead to strategies for the prevention of infection-associated preterm birth

DETERMINATION OF THE FRACTURE ENERGY AND THE FRACTURE RESISTANCE OF INTERFACES

The basic concept and the fracture mechanics methods for determination of the fracture energy and the fracture resistance of interfaces between semi-brittle materials are reviewed. The interfacial fracture energy is derived from the global energy balance concept for crack propagations in an interface, whereas the fracture resistance parameter is based on continuum mechanics models of an interface crack. The method to determine the strength parameters of an interface consists of stress analyses and mechanical tests on pre-cracked specimens of a simple geometry such as layered-bonded bend test specimens

FRACTURE OF CERAMIC-TO-METAL INTERFACES

The methods used for studying fracture at metal-ceramic interfaces are based on fracture mechanical principles. Sandwich-like specimens consisting of two rectangular pieces of ceramic solid-state bonded by a intermediate metal layer and notched or precracked at one interface between the two materials are fractured in a three- or four-point bend test device. The interface fracture energy [MATH]C is obtained from the measured loaddeflection curve, the fracture load, the dimensions of the specimen and by use of a correction function YG which pays regard to the elastic properties of the materials involved and the geometry of the specimen. The fracture behaviour of ceramic-to-metal joints with and without intermediate reaction layers is studied. Internal stresses due to differences in the thermal expansion of the constituents are reduced by microcrack formation. For polycrystalline material transitions a mixed failure mode is observed including both adhesive and cohesive fracture contributions. The fracture energy is influenced by impurity phases and by the microstructure of the interface region. Experiments with combinations of single crystalline niobium and sapphire indicate that the interface fracture energy depends on the crystallographic orientationship of the two crystal surfaces bonded together. It is shown that the work of adhesion is only a very small fraction of the interface fracture energy. The contributions of energy dissipation processes to the fracture energy are discussed in more detail

ON THE INTERFACE CRACK MODELS

Les modèles du continu pour une fissure dans l'interface sont discutés. Les incompatiblités logiques présentes dans le champ de tension du modèle conventionnel, comme par exemple les singularités d'oscillation et les interpénétrations de la surface de fissure, sont éliminées en modifiant les conditions de joints à la pointe de fissure. Un modèle de la pointe de fissure est présenté et discuté par rapport à la dispersion inélastique de l'énergie et le manque d'interfaces de matériaux hétérogènes.The continuum models for an interface crack are reviewed. The logical inconsistencies present in the local stress field of the conventional model, such as the oscillatory singularities and the interpenetration of the crack surfaces, are removed by modifying the boundary conditions at the crack tip. An interpretation of the crack tip models is given and discussed with respect to inelastic energy dissipation during interfacial failure of heterogeneous materials

Tanimoto metric in Tree-SOM for improved representation of mass spectrometry data with an underlying taxonomic structure

Simmuteit S, Schleif F-M, Villmann T, Elssner T. Tanimoto metric in Tree-SOM for improved representation of mass spectrometry data with an underlying taxonomic structure. In: Proceedings of ICMLA 2009. IEEE Press; 2009: 563--567