Dissociation between mitogenicity and immunogenicity of TNP- lipopolysaccharide, a T-independent antigen

Two models have been proposed to explain triggering of B cells by so-called “T-independent antigen.” Feldmann and Basten (1) proposed that the interaction of multiple repeating determinants on polymeric antigens with specific Ig receptors on the B-cell surface is sufficient to provide the signals for division of these cells and differentiation to antibody-forming cells. In contrast, coutinho et al. (2, and see review, 3) have claimed that there is only one signal, a mitogenic signal, receptors acting merely as passive focusing devices to localize the antigen on specific cells where it delivers a mitogenic signal resulting in differentiation to an antibody-producing cell. This model rests primarily on the demonstration that at high concentration all T-independent antigens they have tested are mitogenic for B cells (4-6). Compatible with this hypothesis are the observations that hydrolysis of lipopolysaccharide (LPS) to remove the ester- linked fatty acids of the mitogenic lipid A component abrogates its mitogenic (7,8) activity as well as its ability, when substituted with the TNP hapten, to induce a T-independent anti- TNP response (9). However, alkali treatment of LPS, although not changing its antigenic component (8), may also modify the molecule physically or chemically which could account for loss of immunogenic properties (10). We therefore investigated other reagents which interact with LPS in a more chemically defined manner in an effort to clarify the relationship between the mitogenic and immunogenic properties of this molecule. Polymyxin B (PB) is one of a family of cyclic peptide antibiotics which are bactericidal for most gram-negative bacteria. It prevents the lethal endotoxic activity of LPS (11, 12) and changes the physical structure of LPS (13). We report here that low doses of PB added to cultures of mouse spleen cells inhibit the mitogenic activity of TNP-LPS, a T- independent antigen, and native LPS, but do not suppress the immune response to TNP-LPS. PB interacts with TNP-LPS and LPS causing a physical change in the molecule. In addition, polymyxin-treated LPS is no longer mitogenic. These results suggest a dissociation between the mitogenic and immunogenic properties of TNP-LPS

A phyto-guide to species selection for optimized South African green infrastructure

In South Africa, rapid environmental degeneration caused by anthropogenic pollution poses a major ecological engineering problem, demanding proper resource mitigation strategies. For the treatment of polluted water and degraded soil systems, green infrastructure (GI) offers an effective, sustainable and affordable nature-based alternative to grey infrastructure. An additive benefit within GI, plant species provide enormous potential to treatment; however, species vary substantially in their pollutant removal and hydrologic performance. South African civil engineers tasked with designing GI often lack expertise and knowledge of plant behaviour and ecosystem dynamics. Therefore, this paper proposes a decision framework to facilitate selection for designing local GI in the form of a phyto-guide, based on existing recommendations and knowledge of removal processes and plant behaviour. Interdisciplinarity at the core of the phyto-guide relies on continuous specialist collaboration with each selection criteria, whilst efficiency and sustainability are considered equally important contributors to successful GI functioning. The spread of invasive alien plants, whether accidental or deliberate, negatively impacts an ecosystem’s capacity to deliver goods and services. Thus, the desire to optimize GI by incorporating effective phytoremediators cannot be prioritised over conservation concerns. In addition, this paper seeks to advance the GI limitation of relying solely on previously identified phytoremediators, by including evaluation criteria of beneficial plant traits as well as plant distribution, behaviour and diversity into the decision-making process for optimized GI. It is recommended that future research engages in discovering less invasive, naturally occurring local species as potential phytoremediators, inspired by South Africa’s rich biodiversity and endemism, as well as conveying the importance of consultation with engineers and ecologists for optimized GI

Brane Localization and Stabilization via Regional Physics

Extra-dimensional scenarios have become widespread among particle and gravitational theories of physics to address several outstanding problems, including cosmic acceleration, the weak hierarchy problem, and the quantization of gravity. In general, the topology and geometry of the full spacetime manifold will be non-trivial, even if our ordinary dimensions have the topology of their covering space. Most compact manifolds are inhomogeneous, even if they admit a homogeneous geometry, and it will be physically relevant where in the extra-dimensions one is located. In this letter, we explore the use of both local and global effects in a braneworld scenario to naturally provide position-dependent forces that determine and stabilize the location of a single brane. For illustrative purposes, we consider the 2-dimensional hyperbolic horn and the Euclidean cone as toy models of the extra-dimensional manifold, and add a brane wrapped around one of the two spatial dimensions. We calculate the total energy due to brane tension and bending (extrinsic curvature) as well as that due to the Casimir energy of a bulk scalar satisfying a Dirchlet boundary condition on the brane. From the competition of at least two of these effects there can exist a stable minimum of the effective potential for the brane location. However, on more generic spaces (on which more symmetries are broken) any one of these effects may be sufficient to stabilize the brane. We discuss this as an example of physics that is neither local nor global, but regional.Comment: 4 pages, 2 figures. PRL submitte

A jetlet hierarchy for ideal fluid dynamics

European Research Council Advanced Grant 267382 FCCA

Cone pigments in a North American marsupial, the opossum (Didelphis virginiana)

Only two of the four cone opsin gene families found in vertebrates are represented in contemporary eutherian and marsupial species. Recent genetic studies of two species of South American marsupial detected the presence of representatives from two of the classes of cone opsin genes and the structures of these genes predicted cone pigments with respective peaks in the ultraviolet and long-wavelength portions of the spectrum. The Virginia opossum (Didelphis virginiana), a profoundly nocturnal animal, is the only marsupial species found in North America. The prospects for cone-based vision in this species were examined through recordings of the electroretinogram (ERG), a commonly examined retinal response to photic stimulation. Recorded under flickering-light conditions that elicit signals from cone photoreceptors, the spectral sensitivity of the opossum eye is well accounted for by contributions from the presence of a single cone pigment having peak absorption at 561–562 nm. A series of additional experiments that employed various chromatic adaptation paradigms were conducted in a search for possible contributions from a second (short-wavelength sensitive) cone pigment. We found no evidence that such a mechanism contributes to the ERG in this marsupial

Weak dual pairs and Jetlet methods for ideal incompressible fluid models in n≥2 dimensions

We review the role of dual pairs in mechanics and use them to derive particle-like solutions to regularized incompressible fluid systems. In our case we have a dual pair resulting from the action of diffeomorphisms on point particles (essentially by moving the points). We then augment our dual pair by considering the action of diffeomorphisms on Taylor series, also known as jets. The augmented weak dual pairs induce a hierarchy of particle-like solutions and conservation laws with particles carrying a copy of a jet group. We call these augmented particles jetlets. The jet groups serve as finite-dimensional models of the diffeomorphism group itself, and so the jetlet particles serve as a finite-dimensional model of the self-similarity exhibited by ideal incompressible fluids. The conservation law associated to jetlet solutions is shown to be a shadow of Kelvin’s circulation theorem. Finally, we study the dynamics of infinite time particle mergers. We prove that two merging particles at the zeroth level in the hierarchy yield dynamics which asymptotically approach that of a single particle in the first level in the hierarchy. This merging behavior is then verified numerically as well as the exchange of angular momentum which must occur during a near collision of two particles. The resulting particle-like solutions suggest a new class of meshless methods which work in dimensions [Math Processing Error] n≥2 and which exhibit a shadow of Kelvin’s circulation theorem. More broadly, this provides one of the first finite-dimensional models of self-similarity in ideal fluids

What's in a name; Genetic structure in Solanum section Petota studied using population-genetic tools

Background - The taxonomy and systematic relationships among species of Solanum section Petota are complicated and the section seems overclassified. Many of the presumed (sub)species from South America are very similar and they are able to exchange genetic material. We applied a population genetic approach to evaluate support for subgroups within this material, using AFLP data. Our approach is based on the following assumptions: (i) accessions that may exchange genetic material can be analyzed as if they are part of one gene pool, and (ii) genetic differentiation among species is expected to be higher than within species. Results - A dataset of 566 South-American accessions (encompassing 89 species and subspecies) was analyzed in two steps. First, with the program STRUCTURE 2.2 in an 'unsupervised' procedure, individual accessions were assigned to inferred clusters based on genetic similarity. The results showed that the South American members of section Petota could be arranged in 16 clusters of various size and composition. Next, the accessions within the clusters were grouped by maximizing the partitioning of genetic diversity among subgroups (i.e., maximizing Fst values) for all available individuals of the accessions (2767 genotypes). This two-step approach produced an optimal partitioning into 44 groups. Some of the species clustered as genetically distinct groups, either on their own, or combined with one or more other species. However, accessions of other species were distributed over more than one cluster, and did not form genetically distinct units. Conclusions - We could not find any support for 43 species (almost half of our dataset). For 28 species some level of support could be found varying from good to weak. For 18 species no conclusions could be drawn as the number of accessions included in our dataset was too low. These molecular data should be combined with data from morphological surveys, with geographical distribution data, and with information from crossing experiments to identify natural units at the species level. However, the data do indicate which taxa or combinations of taxa are clearly supported by a distinct set of molecular marker data, leaving other taxa unsupported. Therefore, the approach taken provides a general method to evaluate the taxonomic system in any species complex for which molecular data are available

The biogeography of South African terrestrial plant invasions

Thousands of plant species have been introduced, intentionally and accidentally, to South Africa from many parts of the world. Alien plants are now conspicuous features of many South African landscapes and hundreds of species have naturalised (i.e. reproduce regularly without human intervention), many of which are also invasive (i.e. have spread over long distances). There is no comprehensive inventory of alien, naturalised, and invasive plants for South Africa, but 327 plant taxa, most of which are invasive, are listed in national legislation. We collated records of 759 plant taxa in 126 families and 418 genera that have naturalised in natural and semi-natural ecosystems. Over half of these naturalised taxa are trees or shrubs, just under a tenth are in the families Fabaceae (73 taxa) and Asteraceae (64); genera with the most species are Eucalyptus,Acacia, and Opuntia. The southern African Plant Invaders Atlas (SAPIA) provides the best data for assessing the extent of invasions at the national scale. SAPIA data show that naturalised plants occur in 83% of quarter-degree grid cells in the country. While SAPIA data highlight general distribution patterns (high alien plant species richness in areas with high native plant species richness and around the main human settlements), an accurate, repeatable method for estimating the area invaded by plants is lacking. Introductions and dissemination of alien plants over more than three centuries, and invasions over at least 120 years (and especially in the last 50 years) have shaped the distribution of alien plants in South Africa. Distribution patterns of naturalised and invasive plants define four ecologically-meaningful clusters or “alien plant species assemblage zones”, each with signature alien plant taxa for which trait-environment interactions can be postulated as strong determinants of success. Some widespread invasive taxa occur in high frequencies across multiple zones; these taxa occur mainly in riparian zones and other azonal habitats,or depend on human-mediated disturbance, which weakens or overcomes the factors that determine specificity to any biogeographical region