Transmission electron microscopy at 20 kV for imaging and spectroscopy

The electron optical performance of a transmission electron microscope (TEM) is characterized for direct spatial imaging and spectroscopy using electrons with energies as low as 20 keV. The highly stable instrument is equipped with an electrostatic monochromator and a C(S)-corrector. At 20 kV it shows high image contrast even for single-layer graphene with a lattice transfer of 213 pm (tilted illumination). For 4 nm thick Si, the 200 reflections (271.5 pm) were directly transferred (axial illumination). We show at 20 kV that radiation-sensitive fullerenes (C(60)) within a carbon nanotube container withstand an about two orders of magnitude higher electron dose than at 80 kV. In spectroscopy mode, the monochromated low-energy electron beam enables the acquisition of EELS spectra up to very high energy losses with exceptionally low background noise. Using Si and Ge, we show that 20 kV TEM allows the determination of dielectric properties and narrow band gaps, which were not accessible by TEM so far. These very first results demonstrate that low kV TEM is an exciting new tool for determination of structural and electronic properties of different types of nano-materials.

Pathogenicity of biological control agents for livestock ectoparasites: a simulation analysis

The management of arthropod ectoparasites of livestock currently relies largely on the use of neurotoxic chemicals. However, concerns over the development of resistance, as well as operator and environmental contamination, have stimulated research into alternative approaches to their control, including the use of biological pathogens. The search for suitable pathogens often focuses on identifying the most highly virulent agents for application. However, practical issues such as the ability of a pathogen to penetrate to the skin through hair or wool, tolerance of high skin surface temperatures and high residual activity may mean that the most virulent pathogens are not necessarily the most appropriate for commercial application. Here, a simulation model is constructed and used to highlight a range of key features which characterize suitable pathogens for such application. Sensitivity analysis shows that even a relatively low probability of infection following contact between infectious and susceptible individuals may give acceptable control, providing it is counterbalanced by higher survival of both infected and infectious parasite hosts in order to allow the rate of transmission to exceed the threshold required to suppress parasite population growth. The model highlights the need for studies attempting to identify sustainable biocontrol agents to explore the use of pathogens which have a range of the characteristics that contribute to overall pathogenicity, but which are also most compatible with practical application systems.

Mapping risk foci for endemic sheep scab

Psoroptic mange in sheep, resulting from infestation by the astigmatid mite Psoroptes ovis, is increasingly prevalent in Europe and other parts of the world. As a step towards improved national control, regional or local scab management programmes that target high-risk areas and aim to maintain the number of outbreaks below an acceptable level may be an effective initial use of time and resource. To facilitate such a management approach, in this paper scab outbreak farms are identified using a questionnaire survey of sheep farmers, the data from which are then used to build a national scab risk model for Great Britain. The questionnaire results indicate a national prevalence of scab, between March 2007 and February 2008, of 8.6% (+/-1.98). However, previous exposure to sheep scab significantly affected the respondent's probability of reporting a scab outbreak during the survey period (chi(2)=53.2, d.f.=1, P<0.001); 85% of the farms that reported at least one scab outbreak had experienced outbreaks in previous years, 27% had experienced outbreaks in more than five of the previous 10 years. In contrast, 76% of farms that did not report scab had not had a previous outbreak. The highest prevalence areas were in Northern England, Wales, Southwest England and Scotland. Modelling the distribution of the reported scab outbreaks identified height above sea level, temperature and rainfall as significant predictors of the probability of an outbreak, superimposed on an underlying pattern of sheep abundance. It is argued that scab management programmes directed at these foci have the potential to allow a more targeted approach to scab control and significantly reduce the prevalence of scab in the UK and other European countries.

Targeting the MHC class II pathway of antigen presentation enhances immunogenicity and safety of allergen immunotherapy

BACKGROUND

Current s.c. allergen-specific immunotherapy (SIT) leads to amelioration of IgE-mediated allergy, but it requires numerous allergen injections over several years and is frequently associated with severe side-effects. The aim of this study was to test whether modified recombinant allergens can improve therapeutic efficacy in SIT while reducing allergic side-effects.

METHODS

The major cat allergen Fel d 1 was fused to a TAT-derived protein translocation domain and to a truncated invariant chain for targeting the MHC class II pathway (MAT-Fel d 1). The immunogenicity was evaluated in mice, while potential safety issues were assessed by cellular antigen stimulation test (CAST) using basophils from cat-dander-allergic patients.

RESULTS

MAT-Fel d 1 enhanced induction of Fel d 1-specific IgG2a antibody responses as well as the secretion of IFN-gamma and IL-2 from T cells. Subcutaneous allergen-specific immunotherapy of mice using the modified Fel d 1 provided stronger protection against anaphylaxis than SIT with unmodified Fel d 1, and MAT-Fel d 1 caused less degranulation of human basophils than native Fel d 1.

CONCLUSION

MAT-Fel d 1 allergen enhanced protective antibody and Th1 responses in mice, while reducing human basophil degranulation. Immunotherapy using MAT-Fel d 1 allergen therefore has the potential to enhance SIT efficacy and safety, thus, shortening SIT. This should increase patient compliance and lower treatment costs.

Prospects for aberration-free electron microscopy

Future aberration-corrected electron microscopes that will enable sub-Angstroem spatial and sub-eV energy resolution are outlined . The sub-Angstroem transmission electron microscope (SATEM) only compensates for the spherical aberration and reduces the chromatic aberration disc by means of a monochromator. In order to correct for both aberrations, two novel correctors, the ultracorrector and the superaplanator are proposed which will yield a resolution limit of about 0.5A and a large field of view of more than 4 x 10(6) image points. The superaplanator is best suited for obtaining an achromatic aplanat required for the realization of the high-performance in situ electron microscope of the TEAM project.

The most common chromosome aberration detected by high-resolution comparative genomic hybridization in vulvar intraepithelial neoplasia is not seen in vulvar squamous cell carcinoma

We analyzed genetic changes in condylomas (four cases), vulvar intraepithelial neoplasia I-III (VIN I-III, eleven cases), and primary vulvar squamous cell carcinomas (VSCC, ten cases) by high-resolution comparative genomic hybridization (HR-CGH) and flowcytometry. All samples were also human papilloma virus (HPV)-genotyped. Gain of chromosome 1, the aberration most often seen in VIN III (67%), was not seen in HPV-positive or -negative VSCCs (0%). Both VIN III and VSCC frequently showed gain of 3q (56 and 70%, respectively). The VIN III samples often demonstrated gain of 20q (56%) and 20p (44%), and the VSCC samples gain of 8q (60%), loss of 3p (50%), and 8p (40%). None of the four most frequent changes in the VSCC samples occurred exclusively in the HPV-positive or -negative samples. As expected, we did not find any cytogenetic changes in condylomas and nearly any changes in VIN I-II.

Theory of electron-optical achromats and apochromats

A detailed theoretical formulation of the primary and secondary chromatic aberrations of electron-optical systems with a straight optic axis is outlined. To simplify the mathematical expenditure only systems composed of magnetic round lenses and magnetic and electrostatic quadrupoles are taken into account. By appropriately arranging these elements, it is possible to construct feasible electron-optical analogues of light-optical achromats and apochromats.