Delay of phagosome maturation by a mycobacterial lipid is reversed by nitric oxide.

Mycobacterium tuberculosis is a facultative intracellular pathogen that inhibits phagosome maturation in macrophages thereby securing survival and growth. Mycobacteria reside in an early endocytic compartment of near-neutral pH where they upregulate production of complex glycolipids such as trehalose dimycolate. Here, we report that trehalose dimycolate coated onto beads increased the bead retention in early phagosomes, i.e. at a similar stage as viable mycobacteria. Thus, a single mycobacterial lipid sufficed to divert phagosome maturation and likely contributes to mycobacterial survival in macrophages. Previous studies showed that activated macrophages promote maturation of mycobacterial phagosomes and eliminate mycobacteria through bactericidal effectors including nitric oxide generated by inducible nitric-oxide synthase. We show that deceleration of bead phagosome maturation by trehalose dimycolate was abolished in immune-activated wild type, but not in activated nitric-oxide synthase-deficient macrophages, nor when hydroxyl groups of trehalose dimycolate were chemically modified by reactive nitrogen intermediates. Thus, specific host defence effectors of activated macrophages directly target a specific virulence function of mycobacteria

Real-time imaging of Leishmania mexicana-infected early phagosomes: a study using primary macrophages generated from green fluorescent protein-Rab5 transgenic mice

The small GTPase Rab5 is a key regulator of endosome/phagosome maturation and in intravesicular infections marks a phagosome stage at which decisions over pathogen replication or destruction are integrated. It is currently unclear whether Leishmania-infected phagosomes uniformly pass through a Rab5+ stage on their intracellular path to compartments with late endosomal/early lysosomal characteristics. Differences in routes and final compartments could have consequences for accessibility to antileishmanial drugs. Here, we generated a unique gfp-rab5 transgenic mouse model to visualize Rab5 recruitment to early parasite-containing phagosomes in primary host cells. Using real-time fluorescence imaging of phagosomes carrying Leishmania mexicana, we determined that parasite-infested phagosomes follow a uniform sequence of transient Rab5 recruitment. Residence in Rab5+ compartments was much shorter compared with phagosomes harboring latex beads. Furthermore, a comparative analysis of parasite life-cycle stages and mutants deficient in lpg1, the gene encoding the enzyme required for synthesis of the dominant surface lipophosphoglycan, indicated that parasite surface ligands and host cell receptors modulate pathogen residence times in Rab5+ phagosomes, but, as far as tested, had no significant effect on intracellular L. mexicana survival or replication.—Lippuner, C., Paape, D., Paterou, A., Brand, J., Richardson, M., Smith, A. J., Hoffmann, K., Brinkmann, V., Blackburn, C., Aebischer, T. Real-time imaging of Leishmania mexicana-infected early phagosomes: a study using primary macrophages generated from green fluorescent protein-Rab5 transgenic mice

Resistance to host antimicrobial peptides mediates resilience of gut commensals during infection and aging in Drosophila

Resilience to short-term perturbations, like inflammation, is a fundamental feature of microbiota, yet the underlying mechanisms of microbiota resilience are incompletely understood. Here, we show that Lactiplantibacillus plantarum, a major Drosophila commensal, stably colonizes the fruit fly gut during infection and is resistant to Drosophila antimicrobial peptides (AMPs). By transposon screening, we identified L. plantarum mutants sensitive to AMPs. These mutants were impaired in peptidoglycan O-acetylation or teichoic acid D-alanylation, resulting in increased negative cell surface charge and higher affinity to cationic AMPs. AMP-sensitive mutants were cleared from the gut after infection and aging-induced gut inflammation in wild-type, but not in AMP-deficient flies, suggesting that resistance to host AMPs is essential for commensal resilience in an inflamed gut environment. Thus, our work reveals that in addition to the host immune tolerance to the microbiota, commensal-encoded resilience mechanisms are necessary to maintain the stable association between host and microbiota during inflammation

The IFN-inducible Golgi- and endoplasmic reticulum- associated 47-kDa GTPase IIGP is transiently expressed during listeriosis.

Members of the 47-kDa GTPase family are implicated in an IFN-gamma-induced, as yet unclear, mechanism that confers innate resistance against infection with intracellular pathogens. Overt immunological parameters are apparently uncompromised in mice deficient for individual members and the prototype of this family, IGTP, localizes to the endoplasmic reticulum. This suggests that these GTPases are involved in intracellular defense. We analyzed the expression of the 47-kDa GTPase cognate, IIGP, in splenic sections from mice infected with the intracellular pathogen Listeria monocytogenes by immunohistochemistry. An early transient IIGP induction was observed revealing the IFN-gamma responsiveness of cellular subcompartments within the spleen in early listeriosis. Marginal metallophilic macrophages and endothelial cells within the red and white pulp strongly expressed IIGP, while other splenocytes remained negative. In vitro analyses show that both type I and type II IFNs are prime stimuli for IIGP induction in various cells, including L. monocytogenes-infected or LPS-stimulated macrophages, endothelial cells, and activated T cells. Contrary to the subcellular localization of IGTP, IIGP was predominantly associated with the Golgi apparatus and also localizes to the endoplasmic reticulum. We conclude that IIGP exerts a distinct role in IFN-induced intracellular membrane trafficking or processing

Bilinear noise subtraction at the GEO 600 observatory

We develop a scheme to subtract off bilinear noise from the gravitational wave strain data and demonstrate it at the GEO 600 observatory. Modulations caused by test mass misalignments on longitudinal control signals are observed to have a broadband effect on the mid-frequency detector sensitivity ranging from 50 Hz to 500 Hz. We estimate this bilinear coupling by making use of narrow-band signal injections that are already in place for noise projection purposes. A coherent bilinear signal is constructed by a two-stage system identification process where the involved couplings are approximated in terms of stable rational functions. The time-domain filtering efficiency is observed to depend upon the system identification process especially when the involved transfer functions cover a large dynamic range and have multiple resonant features. We improve upon the existing filter design techniques by employing a Bayesian adaptive directed search strategy that optimizes across the several key parameters that affect the accuracy of the estimated model. The resulting post-offline subtraction leads to a suppression of modulation side-bands around the calibration lines along with a broadband reduction of the mid-frequency noise floor. The filter coefficients are updated periodically to account for any non-stationarities that can arise within the coupling. The observed increase in the astrophysical range and a reduction in the occurrence of non-astrophysical transients suggest that the above method is a viable data cleaning technique for current and future gravitational wave observatories

Novel cell death program leads to neutrophil extracellular traps

Neutrophil extracellular traps (NETs) are extracellular structures composed of chromatin and granule proteins that bind and kill microorganisms. We show that upon stimulation, the nuclei of neutrophils lose their shape, and the eu- and heterochromatin homogenize. Later, the nuclear envelope and the granule membranes disintegrate, allowing the mixing of NET components. Finally, the NETs are released as the cell membrane breaks. This cell death process is distinct from apoptosis and necrosis and depends on the generation of reactive oxygen species (ROS) by NADPH oxidase. Patients with chronic granulomatous disease carry mutations in NADPH oxidase and cannot activate this cell-death pathway or make NETs. This novel ROS-dependent death allows neutrophils to fulfill their antimicrobial function, even beyond their lifespan

Ionization wave propagation on a micro cavity plasma array

Microcavity plasma arrays of inverse pyramidal cavities have been fabricated in p-Si wafers. Each cavity acts as a microscopic dielectric barrier discharge. Operated at atmospheric pressure in argon and excited with high voltage at about 10 kHz, each cavity develops a localized microplasma. Experiments have shown a strong interaction of individual cavities, leading to the propagation of wave-like optical emission structures along the surface of the array. This phenomenon is numerically investigated using computer simulation. The observed ionization wave propagates with a speed of about 5 km/s, which agrees well the experimental findings. It is found that the wave propagation is due to sequential contributions of a drift of electrons followed by drift of ions between cavities seeded by photoemission of electrons by the plasma in adjacent cavities

B Cell-Specific S1PR1 Deficiency Blocks Prion Dissemination between Secondary Lymphoid Organs

Many prion diseases are peripherally acquired (eg. orally or via lesions to skin or mucous membranes). After peripheral exposure prions replicate first upon follicular dendritic cells (FDC) in the draining lymphoid tissue before infecting the brain. However, after replication upon FDC within the draining lymphoid tissue, prions are subsequently propagated to most non-draining secondary lymphoid organs (SLO) including the spleen by a previously underdetermined mechanism. The germinal centres in which FDC are situated produce a population of B cells which can recirculate between SLO. We therefore reasoned that B cells were ideal candidates by which prion dissemination between SLO may occur. Sphingosine 1-phosphate receptor 1 (S1PR1) stimulation controls the egress of T and B cells from SLO. S1PR1 signalling-blockade sequesters lymphocytes within SLO resulting in lymphopenia in the blood and lymph. We show that in mice treated with the S1PR modulator FTY720, or with S1PR1-deficiency restricted to B cells, the dissemination of prions from the draining lymph node to non-draining SLO is blocked. These data suggest that B cells interacting with and acquiring surface proteins from FDC, and recirculating between SLO via the blood and lymph, mediate the initial propagation of prions from the draining lymphoid tissue to peripheral tissues

Angiogenesis is present in experimental autoimmune encephalomyelitis and pro-angiogenic factors are increased in multiple sclerosis lesions

<p>Abstract</p> <p>Background</p> <p>Angiogenesis is a common finding in chronic inflammatory diseases; however, its role in multiple sclerosis (MS) is unclear. Central nervous system lesions from both MS and experimental autoimmune encephalomyelitis (EAE), the animal model of MS, contain T cells, macrophages and activated glia, which can produce pro-angiogenic factors. Previous EAE studies have demonstrated an increase in blood vessels, but differences between the different phases of disease have not been reported. Therefore we examined angiogenic promoting factors in MS and EAE lesions to determine if there were changes in blood vessel density at different stages of EAE.</p> <p>Methods</p> <p>In this series of experiments we used a combination of vascular casting, VEGF ELISA and immunohistochemistry to examine angiogenesis in experimental autoimmune encephalomyelitis (EAE). Using immunohistochemistry we also examined chronic active MS lesions for angiogenic factors.</p> <p>Results</p> <p>Vascular casting and histological examination of the spinal cord and brain of rats with EAE demonstrated that the density of patent blood vessels increased in the lumbar spinal cord during the relapse phase of the disease (p < 0.05). We found an increased expression of VEGF by inflammatory cells and a decrease in the recently described angiogenesis inhibitor meteorin. Examination of chronic active human MS tissues demonstrated glial expression of VEGF and glial and blood vessel expression of the pro-angiogenic receptor VEGFR2. There was a decreased expression of VEGFR1 in the lesions compared to normal white matter.</p> <p>Conclusions</p> <p>These findings reveal that angiogenesis is intimately involved in the progression of EAE and may have a role in MS.</p