Quantification of the effects of antibodies on the extra- and intracellular dynamics of Salmonella enterica.

Antibodies are known to be essential in controlling Salmonella infection, but their exact role remains elusive. We recently developed an in vitro model to investigate the relative efficiency of four different human immunoglobulin G (IgG) subclasses in modulating the interaction of the bacteria with human phagocytes. Our results indicated that different IgG subclasses affect the efficacy of Salmonella uptake by human phagocytes. In this study, we aim to quantify the effects of IgG on intracellular dynamics of infection by combining distributions of bacterial numbers per phagocyte observed by fluorescence microscopy with a mathematical model that simulates the in vitro dynamics. We then use maximum likelihood to estimate the model parameters and compare them across IgG subclasses. The analysis reveals heterogeneity in the division rates of the bacteria, strongly suggesting that a subpopulation of intracellular Salmonella, while visible under the microscope, is not dividing. Clear differences in the observed distributions among the four IgG subclasses are best explained by variations in phagocytosis and intracellular dynamics. We propose and compare potential factors affecting the replication and death of bacteria within phagocytes, and we discuss these results in the light of recent findings on dormancy of Salmonella.

Quantification of the benefits of a streamlined tether for a high-altitude-tethered balloon

A high-altitude tethered balloon (HATB) reaching a height of 20 km has numerous applications including communications, meteorological monitoring, surveillance and, for the current paper, geoengineering. The HATB configuration consists of a 20 km tether rising up from the ground through the troposphere, where the wind-regime can be turbulent and include high-wind velocities due to the jet-stream, up into the more stable stratosphere where the tether would be attached to a spherical balloon. This paper evaluates wind-excited vibration of a HATB and will investigate the advantages of using a streamlined instead of a circular tether profile. Streamlining the tether reduces drag but introduces stability problems and complicates the numerical modelling. Consequently, prior to a thorough investigation of the stability issues due to fluid-structure interaction, a 3D nonlinear lumped-mass HATB model is used to quantify the benefit of a streamlined tether. The benefit is quantified by comparing the system specifications - such as balloon size and the tension in the tether - required to meet certain design requirements driven by the Stratospheric Particle Injection for Climate Engineering (SPICE) project. The SPICE project is investigating the feasibility of climate engineering using a HATB.

Spectroscopic characterization of protein-wrapped single-wall carbon nanotubes and quantification of their cellular uptake in multiple cell generations

We study the spectral characteristics of bovine serum albumin (BSA) protein conjugated single-wall carbon nanotubes (SWNTs), and quantify their uptake by macrophages. The binding of BSA onto the SWNT surface is found to change the protein structure and to increase the doping of the nanotubes. The G-band Raman intensity follows a well-defined power law for SWNT concentrations of up to 33 μg ml-1 in aqueous solutions. Subsequently, in vitro experiments demonstrate that incubation of BSA-SWNT complexes with macrophages affects neither the cellular growth nor the cellular viability over multiple cell generations. Using wide spot Raman spectroscopy as a fast, non-destructive method for statistical quantification, we observe that macrophages effectively uptake BSA-SWNT complexes, with the average number of nanotubes internalized per cell remaining relatively constant over consecutive cell generations. The number of internalized SWNTs is found to be ∼30 × 106 SWNTs/cell for a 60 mm-2 seeding density and ∼100 × 10 6 SWNTs/cell for a 200 mm-2 seeding density. Our results show that BSA-functionalized SWNTs are an efficient molecular transport system with low cytotoxicity maintained over multiple cell generations. © 2013 IOP Publishing Ltd.