Antibodies to Core Lipopolysaccharide Determinants: Absence of Cross-reactivity with Heterologous Lipopolysaccharides

Using monoclonal antibodies directed against defined epitopes of endotoxin core, this study demonstrated that the presentation of lipopolysaccharide (LPS) to antibodies is critical for measuring the specific binding of antibodies to LPS structures. False cross-reactive reactions apparently were observed when free core LPS or lipid A were used as antigens in ELISA, whereas coating with complexes of high-density lipoproteins with core LPS increased both the sensitivity and the specificity of the test compared with coating with free core LPS, so that nonspecific binding of antibodies was largely avoided. Using this technique, it was not possible to find broadly cross-reactive core LPS antibodies after immunization of rabbits and humans with rough mutants of gram-negative bacteria. These observations underscore the need for careful evaluation of the potential for cross-reactivity of antisera and of monoclonal antibodies directed against endotoxin cor

Insights on Water Interaction at the Interface of Nitrogen Functionalized Hydrothermal Carbons

Hydrothermal carbon (HTC) derived from biomass is a class of cost-efficient, eco-friendly functional carbon materials with various potential applications. In this work, solid-state nuclear magnetic resonance (NMR), longitudinal (T1) relaxation time and diffusion NMR were employed to investigate the structure and water dynamics for HTC and nitrogen-functionalized hydrothermal carbon (N-HTC) samples ((N)-HTC). Results showed that the presence of N-functional groups influences the water interaction with (N)-HTC more strongly than surface area, pore size distribution or oxygenated functional groups. Furthermore, the degree of water interaction can be tuned by adjusting the synthesis temperature and the precursor ratio. Water motion was more strongly inhibited in N-HTC than in N-free HTC, thereby suggesting the existence of a differently structured hydration shell around N-HTC particles. In addition, the diffusion data of water in the N-HTC material shows two components that do not exchange on the time scale of the experiment (tens of milliseconds), indicating a significant fraction of slow mobile water that exists inside the structure of N-HTC. 1H–2H isotope exchange and cross-polarization NMR results show this internal water only in a near-surface layer of the N-HTC particles. Based on these findings, a model for water interaction with (N)-HTC particles is proposed

Effects of finite curvature on soliton dynamics in a chain of nonlinear oscillators

We consider a curved chain of nonlinear oscillators and show that the interplay of curvature and nonlinearity leads to a number of qualitative effects. In particular, the energy of nonlinear localized excitations centered on the bending decreases when curvature increases, i.e. bending manifests itself as a trap for excitations. Moreover, the potential of this trap is double-well, thus leading to a symmetry breaking phenomenon: a symmetric stationary state may become unstable and transform into an energetically favorable asymmetric stationary state. The essentials of symmetry breaking are examined analytically for a simplified model. We also demonstrate a threshold character of the scattering process, i.e. transmission, trapping, or reflection of the moving nonlinear excitation passing through the bending.Comment: 13 pages (LaTeX) with 10 figures (EPS

The potential role of ABC transporters as factors influencing drug susceptibility in the salmon louse, Lepeophtheirus salmonis (Kroyer, 1837)

Efficient control of sea lice is a major challenge for the sustainable production of farmed Atlantic salmon (Salmo salar (Linnaeus, 1758)). These marine ectoparasites feed on mucus, skin and blood of their hosts, thereby reducing the salmon’s growth rate and overall health. In the northern hemisphere, the most prevalent species is Lepeophtheirus salmonis (Krøyer, 1837). In 2006, global costs of sea lice infections are estimated to have exceeded €300 million, with the majority spent on a limited number of chemical delousing agents. Emamectin benzoate (EMB; SLICE®), an avermectin, has been widely used since its introduction in 2000, due to its convenient administration as an in-feed medication and its high efficacy against all parasitic stages of L. salmonis. However, over-reliance on a single or limited range of medicines favours the emergence of drug resistance and, as a result, the efficacy of this compound in treating L. salmonis has decreased in recent years, as reported from e.g. Chile, Norway, Scotland and Canada. Declining efficacy underlines the need for an improved understanding of the molecular mechanisms underlying EMB drug resistance in L. salmonis. Elucidation of these mechanisms would allow for improved monitoring tools, earlier detection of developing resistance, extended usability of current delousing agents and development of new parasiticides. The work described in this thesis sets out to examine the molecular mechanisms underlying EMB resistance in L. salmonis. In earlier studies, research in nematodes and arthropods has linked drug efflux transporters belonging to the family of ATP-binding cassette (ABC) transporters to ivermectin (IVM) resistance, a parasiticide with high chemical similarity to EMB. ABC transporters such as permeability glycoprotein (P-gp), transport a wide range of substrates, including drugs, and have been suggested to provide a potential molecular mechanism through which EMB resistance might be mediated in sea lice. As an example of such mechanisms, increased expression of P-gp is one of the causative factors for drug resistance in human cancer cells and avermectin resistance in nematode parasites such as Caenorhabditis elegans or Haemonchus contortus. Initial research involved screening for novel salmon lice P-gps that might contribute to EMB resistance. A novel P-gp, SL-PGY1, was discovered using a combined bioinformatic and molecular biological approach. The expression was compared in two well-characterised L. salmonis strains differing in their susceptibility to EMB (S = susceptible, R = resistant). Prior to EMB exposure, mRNA levels did not differ from each other, while, after 24 h exposure, a 2.9-fold increase in SL-PGY1 mRNA expression was observed in the R strain. SL-PGY1 appears not to be a major factor contributing to reduced EMB susceptibility, although it could play a role, as expression levels increased upon exposure to EMB. A further four additional drug transporters (ABC C subfamily) were also discovered showing high homology to multidrug-resistance proteins (MRP). The relative expression levels of each MRP was compared in the strains S and R, before and after exposure to EMB. No significant changes were found in their expression patterns. If ABC drug transporters mediate the efflux of EMB and thereby reduce the intracellular concentrations of the drug in exposed animals, the inhibition of those ABC drug transporters was expected to lead to higher intracellular levels of EMB. This could result in an enhanced toxic effect when EMB is co-administered with an inhibitor. Two known inhibitors of human P-gps and MRPs, cyclosporin A (CSA) and verapamil (VER), were co-administered with EMB. CSA increased the toxic effect of EMB in both tested strains, implying that the targets of CSA are expressed at comparable levels and that they may be part of the mechanism conferring EMB resistance. VER increased the toxic effect of EMB in the R strain, but had no significant effects on the S strain. This implies that the expression of factors inhibited by VER differs between the two L. salmonis strains. It is hypothesised that a number of ABC transporters with distinct, yet overlapping patterns of inhibitor specificity are affected by those inhibitors. The search for drug-resistance conferring genes was complemented with a systematic, genome-wide survey of ABC transporters in L. salmonis to find additional members of this important gene family. Next-generation high-throughput RNA sequencing (RNA-seq) was employed to assemble a reference transcriptome from pooled total RNA of salmon lice at different development stages. The transcriptome was assembled against the L. salmonis genome and annotated. Thirty-nine putative ABC transporters were found. Of further interest were transcripts of the subfamily B, C and G, as they contain drug-transporting ABC proteins. For the ABC B subfamily, one full (SL-PGY1) and three half transporter transcripts were found. Only full transporters are known to transport drugs and SL-PGY1 is apparently not a major factor contributing to EMB resistance. Fourteen ABCC sequences were found – 11 MRPs and 3 homologues to sulfonylurea receptors. Of interest are MRPs, as they contribute to drug detoxification in humans and invertebrates. Four MRPs had been identified previously and their expression ratios did not differ between S and R strain parasites. Seven sequences belonging to ABCG subfamily were found. However, none of the L. salmonis ABCG transcripts identified showed sufficient homology to known drug transporters in other species. With the currently limited understanding of the mechanisms conferring EMB resistance, monitoring the susceptibility of L. salmonis subpopulations is essential. Dose-response bioassays are currently widely used. Tests with pre-adult II or adult parasites requires relatively large numbers of parasites (~150) to conduct this type of bioassay, which may not always be available. Addressing this issue, we tested the feasibility of a single-dose bioassay (requiring fewer test animals than dose-response bioassays) to discriminate between L. salmonis strains with differing EMB susceptibility. This alternative approach uses time-course toxicity analysis, where the toxic effect of EMB is monitored over time. After clearly defining the effect criteria, we found that it is possible to discriminate between those L. salmonis strains. However, while requiring fewer test animals, time course toxicity analysis is more labour-intensive, but the alternative design can be suitable under certain circumstances. The work reported here has provided new knowledge concerning the mechanisms of EMB resistance in sea lice. Several novel putative drug transporters have been identified, an important first step toward unravelling the complex interactions of genes involved in EMB resistance in this commercially important parasite

Exact Solution of an Evolutionary Model without Ageing

We introduce an age-structured asexual population model containing all the relevant features of evolutionary ageing theories. Beneficial as well as deleterious mutations, heredity and arbitrary fecundity are present and managed by natural selection. An exact solution without ageing is found. We show that fertility is associated with generalized forms of the Fibonacci sequence, while mutations and natural selection are merged into an integral equation which is solved by Fourier series. Average survival probabilities and Malthusian growth exponents are calculated indicating that the system may exhibit mutational meltdown. The relevance of the model in the context of fissile reproduction groups as many protozoa and coelenterates is discussed.Comment: LaTeX file, 15 pages, 2 ps figures, to appear in Phys. Rev.

Monte Carlo simulation of subsurface ordering kinetics in an fcc-alloy model

Within the atom-vacancy exchange mechanism in a nearest-neighbor interaction model we investigate the kinetics of surface-induced ordering processes close to the (001) surface of an fcc A_3B-alloy. After a sudden quench into the ordered phase with a final temperature above the ordering spinodal, T_f > T_sp, the early time kinetics is dominated by a segregation front which propagates into the bulk with nearly constant velocity. Below the spinodal, T_f < T_sp, motion of the segregation wave reflects a coarsening process which appears to be slower than predicted by the Lifschitz-Allen-Cahn law. In addition, in the front-penetrated region lateral growth differs distinctly from perpendicular growth, as a result of the special structure of antiphase boundaries near the surface. Our results are compared with recent experiments on the subsurface ordering kinetics at Cu_3Au (001).Comment: 10 pages, 9 figures, submitted to Phys. Rev. B, in prin

Attributing scientific and technical progress: the case of holography

Holography, the three-dimensional imaging technology, was portrayed widely as a paradigm of progress during its decade of explosive expansion 1964–73, and during its subsequent consolidation for commercial and artistic uses up to the mid 1980s. An unusually seductive and prolific subject, holography successively spawned scientific insights, putative applications and new constituencies of practitioners and consumers. Waves of forecasts, associated with different sponsors and user communities, cast holography as a field on the verge of success—but with the dimensions of success repeatedly refashioned. This retargeting of the subject represented a degree of cynical marketeering, but was underpinned by implicit confidence in philosophical positivism and faith in technological progressivism. Each of its communities defined success in terms of expansion, and anticipated continual progressive increase. This paper discusses the contrasting definitions of progress in holography, and how they were fashioned in changing contexts. Focusing equally on reputed ‘failures’ of some aspects of the subject, it explores the varied attributes by which success and failure were linked with progress by different technical communities. This important case illuminates the peculiar post-World War II environment that melded the military, commercial and popular engagement with scientific and technological subjects, and the competing criteria by which they assessed the products of science