Microbes bind complement inhibitor factor H via a common site

To cause infections microbes need to evade host defense systems, one of these being the evolutionarily old and important arm of innate immunity, the alternative pathway of complement. It can attack all kinds of targets and is tightly controlled in plasma and on host cells by plasma complement regulator factor H (FH). FH binds simultaneously to host cell surface structures such as heparin or glycosaminoglycans via domain 20 and to the main complement opsonin C3b via domain 19. Many pathogenic microbes protect themselves from complement by recruiting host FH. We analyzed how and why different microbes bind FH via domains 19–20 (FH19-20). We used a selection of FH19-20 point mutants to reveal the binding sites of several microbial proteins and whole microbes (Haemophilus influenzae, Bordetella pertussis, Pseudomonas aeruginosa, Streptococcus pneumonia, Candida albicans, Borrelia burgdorferi, and Borrelia hermsii). We show that all studied microbes use the same binding region located on one side of domain 20. Binding of FH to the microbial proteins was inhibited with heparin showing that the common microbial binding site overlaps with the heparin site needed for efficient binding of FH to host cells. Surprisingly, the microbial proteins enhanced binding of FH19-20 to C3b and down-regulation of complement activation. We show that this is caused by formation of a tripartite complex between the microbial protein, FH, and C3b. In this study we reveal that seven microbes representing different phyla utilize a common binding site on the domain 20 of FH for complement evasion. Binding via this site not only mimics the glycosaminoglycans of the host cells, but also enhances function of FH on the microbial surfaces via the novel mechanism of tripartite complex formation. This is a unique example of convergent evolution resulting in enhanced immune evasion of important pathogens via utilization of a “superevasion site.”

Complement is an important arm of innate immunity. Activation of this plasma protein cascade leads to opsonization of targets for phagocytosis, direct lysis of Gram-negative bacteria, and enhancement of the inflammatory and acquired immune responses. No specific signal is needed for activation of the alternative pathway of complement, leading to its activation on all unprotected surfaces. Pathogenic microbes need to evade this pathway, and several species are known to recruit host complement inhibitor factor H (FH) to prevent the activation. FH is important for protection of host cells, too, as defects in FH lead to a severe autoreactive disease, atypical hemolytic uremic syndrome. We have now identified at the molecular level a common mechanism by which seven different microbes, Haemophilus influenzae, Bordetella pertussis, Pseudomonas aeruginosa, Streptococcus pneumoniae, Candida albicans, Borrelia burgdorferi and B. hermsii, recruit FH. All microbes bind FH via a common site on domain 20, which facilitates formation of a tripartite complex between the microbial protein, the main complement opsonin C3b, and FH. We show that, by utilizing the common microbial binding site on FH20, microbes can inhibit complement more efficiently. This detailed knowledge on mechanism of complement evasion can be used in developing novel antimicrobial chemotherapy.

Distribution of plasmoids in high-Lundquist-number magnetic reconnection

The distribution function f(ψ) of magnetic flux ψ in plasmoids formed in high-Lundquist-number current sheets is studied by means of an analytic phenomenological model and direct numerical simulations. The distribution function is shown to follow a power law f(ψ)∼ψ(-1), which differs from other recent theoretical predictions. Physical explanations are given for the discrepant predictions of other theoretical models.

Effects of high-fat diet feeding on Znt8-null mice: differences between β-cell and global knockout of Znt8

Genomewide association studies have linked a polymorphism in the zinc transporter 8 (Znt8) gene to higher risk of developing type 2 diabetes. Znt8 is highly expressed in pancreatic β-cells where it is involved in the regulation of zinc transport into granules. However, Znt8 is also expressed in other tissues including α-cells, where its function is as yet unknown. Previous work demonstrated that mice lacking Znt8 globally were more susceptible to diet-induced obesity (Lemaire et al., Proc Natl Acad Sci USA 106: 14872-14877, 2009; Nicolson et al., Diabetes 58: 2070-2083, 2009). Therefore, the main goal of this study was to examine the physiological impact of β-cell-specific Znt8 deficiency in mice during high-fat high-calorie (HFHC) diet feeding. For these studies, we used β-cell-specific Znt8 knockout (Ins2Cre:Znt8loxP/loxP) and whole body Znt8 knockout (Cre-:Znt8(-/-)) mice placed on a HFHC diet for 16 wk. Ins2Cre:Znt8loxP/loxP mice on HFHC diet had similar body weights throughout the study but displayed impaired insulin biosynthesis and secretion and were glucose intolerant compared with littermate control Ins2Cre mice. In contrast, Cre-:Znt8(-/-) mice became remarkably obese, hyperglycemic, hyperinsulinemic, insulin resistant, and glucose intolerant compared with littermate control Cre- mice. These data show that β-cell Znt8 alone does not considerably aggravate weight gain and glucose intolerance during metabolic stress imposed by an HFHC diet. However, global loss of Znt8 is involved in exacerbating diet-induced obesity and resulting insulin resistance, and this may be due to the loss of Znt8 activity in a tissue other than the β-cell. Thus, our data suggest that Znt8 contributes to the risk of developing type 2 diabetes through β-cell- and non-β-cell-specific effects.

The antipsychotic drug loxapine is an opener of the sodium-activated potassium channel slack (Slo2.2)

Sodium-activated potassium (K(Na)) channels have been suggested to set the resting potential, to modulate slow after-hyperpolarizations, and to control bursting behavior or spike frequency adaptation (Trends Neurosci 28:422-428, 2005). One of the genes that encodes K(Na) channels is called Slack (Kcnt1, Slo2.2). Studies found that Slack channels were highly expressed in nociceptive dorsal root ganglion neurons and modulated their firing frequency (J Neurosci 30:14165-14172, 2010). Therefore, Slack channel openers are of significant interest as putative analgesic drugs. We screened the library of pharmacologically active compounds with recombinant human Slack channels expressed in Chinese hamster ovary cells, by using rubidium efflux measurements with atomic absorption spectrometry. Riluzole at 500 μM was used as a reference agonist. The antipsychotic drug loxapine and the anthelmintic drug niclosamide were both found to activate Slack channels, which was confirmed by using manual patch-clamp analyses (EC(50) = 4.4 μM and EC(50) = 2.9 μM, respectively). Psychotropic drugs structurally related to loxapine were also evaluated in patch-clamp experiments, but none was found to be as active as loxapine. Loxapine properties were confirmed at the single-channel level with recombinant rat Slack channels. In dorsal root ganglion neurons, loxapine was found to behave as an opener of native K(Na) channels and to increase the rheobase of action potential. This study identifies new K(Na) channel pharmacological tools, which will be useful for further Slack channel investigations.

Fast magnetic reconnection in laser-produced plasma bubbles

Recent experiments have observed magnetic reconnection in high-energy-density, laser-produced plasma bubbles, with reconnection rates observed to be much higher than can be explained by classical theory. Based on fully kinetic particle simulations we find that fast reconnection in these strongly driven systems can be explained by magnetic flux pileup at the shoulder of the current sheet and subsequent fast reconnection via two-fluid, collisionless mechanisms. In the strong drive regime with two-fluid effects, we find that the ultimate reconnection time is insensitive to the nominal system Alfvén time.

Turbulence and bias-induced flows in simple magnetized toroidal plasmas

Turbulence and bias-induced flows in simple magnetized toroidal plasmas are explored with global three-dimensional fluid simulations, focusing on the parameters of the Helimak experiment. The simulations show that plasma turbulence and transport in the regime of interest are dominated by the ideal interchange instability. The application of a bias voltage alters the structure of the plasma potential, resulting in the equilibrium sheared flows.These bias-induced vertical flows located in the gradient region appear to reduce the radial extent of turbulent structures,and thereby lower the radial plasma transport on the low field side.

Targeted resequencing of a genomic region influencing tameness and aggression reveals multiple signals of positive selection

The identification of the causative genetic variants in quantitative trait loci (QTL) influencing phenotypic traits is challenging, especially in crosses between outbred strains. We have previously identified several QTL influencing tameness and aggression in a cross between two lines of wild-derived, outbred rats (Rattus norvegicus) selected for their behavior towards humans. Here, we use targeted sequence capture and massively parallel sequencing of all genes in the strongest QTL in the founder animals of the cross. We identify many novel sequence variants, several of which are potentially functionally relevant. The QTL contains several regions where either the tame or the aggressive founders contain no sequence variation, and two regions where alternative haplotypes are fixed between the founders. A re-analysis of the QTL signal showed that the causative site is likely to be fixed among the tame founder animals, but that several causative alleles may segregate among the aggressive founder animals. Using a formal test for the detection of positive selection, we find 10 putative positively selected regions, some of which are close to genes known to influence behavior. Together, these results show that the QTL is probably not caused by a single selected site, but may instead represent the joint effects of several sites that were targets of polygenic selection.

Observation on integron carriage among clinical isolates of Klebsiella pneumoniae producing extended-spectrum beta-lactamases

PURPOSE

Klebsiella pneumoniae is considered an important pathogen causing nosocomial and community-acquired infections and is often associated with the production of extended-spectrum beta-lactamases (ESBL) belonging to SHV and CTX-M families, which are frequently described as a part of complex integrons, facilitate their horizontal transfer to other related as well as unrelated microbes. The present study was undertaken to investigate the occurrence and characterization of integrons among K pneumoniae isolates producing ESBL in a tertiary referral hospital.

MATERIALS AND METHODS

A total of 136 clinical isolates of K pneumoniae were investigated for the presence of ESBL. Their ESBL genes were characterized by multiplex polymerase chain reaction (PCR). Integrase gene PCR was performed to detect the presence of integron. The isolates were further typed by random amplification of polymorphic DNA (RAPD).

RESULT

Out of 136 K pneumoniae isolates, 63 (46%) were confirmed to be ESBL producers. SHV (68%) and CTX-M (67%) ESBL genes were the most common in our study. Of the 63 ESBL-positive isolates, 58 (92%) strains carried integrons; 52 strains (82%) carried only class 1 integron, whereas 6 (9%) isolates harboured both class 2 integrons and the class 1 gene. However, in ESBL negatives, only 29 (40%) strains were positive for class 1 integron and none for class 2 integron.

CONCLUSION

The presence of class 2 integron amongst ESBL-producing K pneumoniae is being described for the first time in this part of the world. The findings of this study strongly suggest that integrons have a role in the dissemination of ESBL-mediated resistance among the nosocomial isolates of K pneumonia.

Beta cell-specific Znt8 deletion in mice causes marked defects in insulin processing, crystallisation and secretion

AIMS/HYPOTHESIS

Zinc is highly concentrated in pancreatic beta cells, is critical for normal insulin storage and may regulate glucagon secretion from alpha cells. Zinc transport family member 8 (ZnT8) is a zinc efflux transporter that is highly abundant in beta cells. Polymorphisms of ZnT8 (also known as SLC30A8) gene in man are associated with increased risk of type 2 diabetes. While global Znt8 knockout (Znt8KO) mice have been characterised, ZnT8 is also present in other islet cell types and extra-pancreatic tissues. Therefore, it is important to find ways of understanding the role of ZnT8 in beta and alpha cells without the difficulties caused by the confounding effects of ZnT8 in these other tissues.

METHODS

We generated mice with beta cell-specific (Znt8BKO) and alpha cell-specific (Znt8AKO) knockout of Znt8, and performed in vivo and in vitro characterisation of the phenotypes to determine the functional and anatomical impact of ZnT8 in these cells. Thus we assessed zinc accumulation, insulin granule morphology, insulin biosynthesis and secretion, and glucose homeostasis.

RESULTS

Znt8BKO mice are glucose-intolerant, have reduced beta cell zinc accumulation and atypical insulin granules. They also display reduced first-phase glucose-stimulated insulin secretion, reduced insulin processing enzyme transcripts and increased proinsulin levels. In contrast, Znt8AKO mice show no evident abnormalities in plasma glucagon and glucose homeostasis.

CONCLUSIONS/INTERPRETATION

This is the first report of specific beta and alpha cell deletion of Znt8. Our data indicate that while, under the conditions studied, ZnT8 is absolutely essential for proper beta cell function, it is largely dispensable for alpha cell function.

Etiological factors for the persistence of endemic goiter in selected areas of Siddharthnagar district in Eastern Uttar Pradesh, India

AIM

To assess the prevalence of goiter, state of iodine nutrition of the population, consumption pattern of common goitrogenic food, and distribution of iodine through edible salt in selected CD Blocks of Siddharthnagar district in Eastern Uttar Pradesh.

METHODS

Goiter survey among 1,862 school children, aged 6-12 years, of both sexes, and analysis of iodine (I) and thiocyanate (SCN) in 240 urine samples, and iodine content in 210 edible salt samples collected from the selected study areas.

RESULTS

The prevalence of goiter was 26.3% (grade 1: 23.2%; grade 2: 3.1%). Median urinary iodine level was 6.0 microg/dl, and 42% had concentration < 5 microg/dl. Mean (SD) urinary SCN was 0.75 (0.4) mg/dl. Only17.1% of salt samples had iodine level > 15 ppm; 82.9% had < 15 ppm.

CONCLUSION

Consumption of inadequately iodized salt and cyanogenic plant foods containing goitrogenic/anti-thyroidal substances by the people of the studied region are possible reasons for the persistence of goiter during the post salt iodination phase.

Pressure-induced hysteresis in the high spin [Formula: see text] low spin transition in bis(2,4-bis(pyridin-2-yl)thiazole) iron(II) tetrafluoroborate

Studies of the spin transition behavior of the mononuclear compound [Fe(pythiaz)(2)](BF(4))(2) have been carried out under hydrostatic pressures up to 9.13 kbar in the 5-300 K temperature range. Under ambient pressure this compound exhibits an approximately half-step (incomplete) HS [Formula: see text] LS transition with T(1/2) = 146 K without any thermal hysteresis. At pressures up to 4.5 kbar the behavior remains similar but with an upward displacement of T(1/2) and a slight decrease in the residual high spin fraction at low T. Application of higher pressures resulted in an almost complete two-step spin transition with several unusual pressure effects. Along with the expected pressure dependence of T(1/2) the surprising appearance of hysteresis in the spin transition curves was observed. It is suggested that the likely origin of this unprecedented behavior is a pressure-induced structural change.

Increased prevalence of extended spectrum beta lactamase producers in neonatal septicaemic cases at a tertiary referral hospital

Emergence of extended spectrum beta lactamases (ESBLs) producing strains of gram negative bacteria, as one of the leading cause of septicaemia often complicates the clinical and therapeutic outcome. The present study was undertaken to investigate the prevalence of ESBLs in bacteria isolated from neonatal septicaemic cases along with their antimicrobial sensitivity pattern. Blood samples were collected from 243 suspected cases of neonatal septicaemia. Apart from susceptibility testing, all the gram negative isolates were subjected to phenotypic tests for ESBL production. Amongst the positive test samples (n = 115), 84 were gram negative rods. ESBL was detected in 26 (32%) isolates. Results indicate that routine ESBL detection should be made imperative and empirical use of third generation cephalosporins must be discouraged.

Goiter prevalence and iodine nutritional status of school children in a sub-Himalayan Tarai region of eastern Uttar Pradesh

OBJECTIVES

The present work was undertaken to evaluate the prevalence of goiter, state of iodine nutrition of the population, distribution of iodine through edible salt, bioavailability of iodine, consumption of common goitrogenic food that generally interfere with iodine nutrition in Naugarh sub-division of Siddharthnagar district in Uttar Pradesh, India.

SETTING

Five areas were selected from 5 Community Development (CD) Blocks taking one from each by purposive sampling method. In each area, Primary and Junior high schools were selected by simple random sampling to get representative target population.

METHODS

Clinical goiter survey was conducted in 1663 school-aged children from both sexes (6-12 yrs), along with the biochemical analysis of iodine (I) and thiocyanate (SCN) in 200 urine samples, iodine content in 175 edible salt samples and 20 water samples collected from the selected study areas.

RESULTS

The studied region is severely affected by Iodine deficiency disorders (IDD) as goiter prevalence is 30.2% (grade 1: 27.1% grade 2:3.1%). Median urinary iodine level was 96 microg/L indicating biochemical iodine deficiency. The mean urinary thiocyanate was 0.810+/-0.490 mg/dL and mean of I/SCN ratios in all the studied areas were above the critical level of 7. However, 22% of the individual had I/SCN ratio <or=7 indicating their susceptibility for the development of goiter. Only 12.6% of the salt samples had adequate iodine i.e., >or=15 ppm while iodine content in drinking water varied between 7.5-10.7 microg/L.

CONCLUSION

Iodine deficiency is the primary cause, however the consumption of cyanogenic food may have important role for the persistence of IDD in the studied region during post salt iodization phase.