106 research outputs found
An old tool and a new challenge for depicting antenna array radiation patterns
No full textThis paper is intended for teachers and students dealing with antenna engineering. Graphical tools have historically been used for illustrating many basic features of radiation patterns, such as the position and number of secondary lobes, null angles, and beam steering. This paper describes one of these graphical devices, which has been successfully used by the author as a classroom demonstration in many undergraduate antenna courses. In addition, this traditional demonstration is also discussed in the context of modern computer software, such as MATLAB.LEM
« Ardashir’s Eastern Campaign and the Numismatic Evidence », in : J. Cribb, G. Herrmann, eds., After Alexander. Central Asia before Islam. Oxford, Oxford University Press, 2007, pp. 227-242. (Proceedings of the British Academy, 133)
No full textLes informations des sources écrites (Tabari, Nihayat) sur la chronologie des évènements après la victoire d’Ardašīr Ier sur Artaban IV sont contradictoires, avant tout en ce qui concerne la campagne d’Ardašīr Ier à l’est, à Sakastan et Merw. L’A. essaie de reconstruire l’histoire de cette campagne à l’aide d’une analyse du monnayage d’Ardašīr Ier. Les résultats sont les suivants : la campagne est à dater après la prise de Ctesiphon et la guerre contre Severus Alexander. En 233, le règne du r..
Design of bioartificial Poly(ethylene glycol)-based hydrogels for cell culture: tailoring adhesion and degradation
No full textThis work aimed for the design of bioartificial hydrogels based on PEG as cell culture matrices to address the lack of adhesion and create a dynamic, degradable scaffold to mimic the natural environment of cells and simultaneously act as a reservoir for signalling molecules to stimulate specific cellular behaviour. For this charged moieties were integrated into the network through two different pathways – asymmetric block extension of the building block 4-arm PEG-SH with charged monomers like poly(dehydroalanine) or poly(N-[3-(dimethylamino)- propyl]acrylamide) and the design of charged bisacrylic crosslinkers which additionally favoured inherent and tuneable hydrolytic degradation. The so-obtained modified PEG-based hydrogels offered a toolbox of modifications that showed excellent and diverse adsorption properties – from model dyes to more complex bio molecules like growth factors, which simulates the function of the ECM as reservoir for signalling molecules which finally led to improved cell adhesion and viability and directional cell cultivation
Experimental dissection of Candida albicans-host-microbiota interactions in models mimicking the intestinal epithelial barrier
No full textThe fungus Candida albicans is a common member of the healthy human microbiota. However, under certain predisposing conditions, C. albicans can cause infections (candidiasis) ranging from very frequent superficial infections impacting quality of life to life-threatening systemic diseases. Invasive or systemic candidiasis is one the leading causes of nosocomial infections worldwide. The human intestine plays a crucial role in this context since it is the primary reservoir of commensal C. albicans cells, but also the main niche where systemic infections originate. Given the clinical impact of systemic candidiasis, understanding the biology of C. albicans in the intestine as both a commensal and a pathogen is crucial. This includes characterizing the fungal interactions with the microbiota, intestinal environment, intestinal epithelial barrier and immune system. In this thesis, I investigated the fungal-host-microbiota interactions in vitro, explored strategies towards the development of new prophylactic applications against systemic candidiasis, and further developed a state-of-the-art in vitro intestine-on-chip model to study these interactions.Commensal bacteria of the human microbiota, such as Lactobacillus rhamnosus, can antagonize C. albicans pathogenicity. The first part of the thesis aimed to characterize the molecular mechanisms that mediate this antagonism.Der Pilz Candida albicans ist ein Bestandteil des gesunden menschlichen Mikrobioms. Jedoch kann C. albicans unter bestimmten Bedingungen Infektionen (Candidose) verursachen, die von häufig auftretenden, oberflächlichen Infektionen, welche die Lebensqualität beeinträchtigen, bis hin zu lebensbedrohlichen systemischen Erkrankungen reichen. Die invasive oder systemische Candidose ist weltweit eine der häufigsten Ursachen für nosokomiale Infektionen. Der menschliche Darm spielt in diesem Zusammenhang eine entscheidende Rolle, da dies die primäre Nische für kommensale C. albicans ist und die endogene Quelle für systemische Infektionen darstellt. Angesichts der klinischen Relevanz der systemischen Candidose ist es von entscheidender Bedeutung, die Biologie von C. albicans im Darm sowohl als kommensaler Bewohner als auch als Krankheitserreger zu verstehen. Dazu gehört die Charakterisierung der Pilz-Interaktionen mit dem Mikrobiom, der Darmumgebung, der intestinalen Epithelbarriere und dem Immunsystem. Im Rahmen meiner Dissertation habe ich die Interaktionen zwischen Pilz, Wirt und Mikrobiom in vitro untersucht und Strategien zur Entwicklung neuer prophylaktischer Anwendungen gegen systemische Candidose erforscht. Darüber hinaus habe ich ein state-of-the-art in-vitro Darm-Chip-Modell zur Untersuchung dieser Interaktionen entwickelt. Kommensale Bakterien des menschlichen Mikrobioms wie Lactobacillus rhamnosus können der Pathogenität von C. albicans entgegenwirken. Ziel des ersten Teils dieser Doktorarbeit war es, die molekularen Mechanismen zu charakterisierten, die diesem Antagonismus zugrunde liegen
Functional integration of natural killer cells in a microfluidically perfused liver on-a-chip model.
No full textOBJECTIVE
The liver acts as an innate immunity-dominant organ and natural killer (NK) cells, are the main lymphocyte population in the human liver. NK cells are in close interaction with other immune cells, acting as the first line of defense against pathogens, infections, and injury. A previously developed, three-dimensional, perfused liver-on-a-chip comprised of human cells was used to integrate NK cells, representing pivotal immune cells during liver injury and regeneration. The objective of this study was to integrate functional NK cells in an in vitro model of the human liver and assess utilization of the model for NK cell-dependent studies of liver inflammation.
RESULTS
NK cells from human blood and liver specimen were isolated by Percoll separation with subsequent magnetic cell separation (MACS), yielding highly purified blood and liver derived NK cells. After stimulation with toll-like-receptor (TLR) agonists (lipopolysaccharides, Pam3CSK4), isolated NK cells showed increased interferon (IFN)-gamma secretion. To study the role of NK cells in a complex hepatic environment, these cells were integrated in the vascular compartment of a microfluidically supported liver-on-a-chip model in close interaction with endothelial and resident macrophages. Successful, functional integration of NK cells was verified by immunofluorescence staining (NKp46), flow cytometry analysis and TLR agonist-dependent secretion of interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha. Lastly, we observed that inflammatory activation of NK cells in the liver-on-a-chip led to a loss of vascular barrier integrity. Overall, our data shows the first successful, functional integration of NK cells in a liver-on-a-chip model that can be utilized to investigate NK cell-dependent effects on liver inflammation in vitro
Intracellular persistence of Staphylococcus aureus in peripheral immune cells
No full textS. aureus is a causative agent for many diseases, including sepsis. There is increasing evidence that S. aureus is able to persist intracellularly in immune cells leading to chronic,infections. Thus, peripheral immune cells could act as ‘Trojan horses’, offering S. aureus protection. Further, there is evidence that a phenotype switch to SCVs promotes intracellular persistence. The focus of this study was to characterise the potential of peripheral immune cells as a putative niche for S. aureus persistence. Therefore, the interaction of S. aureus with PMN and monocytes isolated from human donors was systematically investigated The influence of the agr of S. aureus, which controls the main virulence factors, was tested using an S. aureus agr knock-out strain as a surrogate for SCVs. The results reveal that S. aureus was capable of infecting peripheral immune cells. Initially, the bacteria were equally internalised by monocytes and PMN in the early phase of infection. Bacterial clearance differed between wildtype and agr k.o. strain with the agr mutant being less efficiently cleared by both professional phagocytes. Moreover, S. aureus was able to persist in peripheral immune cells for up to 24 h p.i. During bacterial persistence, the agr mutant strain had significant advantages to survive demonstrated by a higher bacterial burden within both immune cell types. Monocytes were characterised as the preferred bacterial persistence niche of both immune cell types. In both immune cell types, agr deficient S. aureus generated a lower ROS signal compared to wildtype infected immune cells during the pathogen’s establishment of persistence. This supports the observed reduced immune clearance of intracellular agr deficient bacteria. Overall, entering a dormant state by downregulation of the agr operon represents a potential advantage for the pathogen to disseminate via high-jacking peripheral immune cells as potential vectors of transmission
An immunocompetent intestine-on-chip model as platform for the dissection of host-microbiota interaction
No full textAn alteration of the intestinal community called dysbiosis is associated with a range of conditions such as neurological diseases, diabetes, and inflammatory bowel diseases (IBD). Recently, organ-on-chip (OoC) platforms have been established, which mimic organ-specific physiological microenvironments. By making use of microfluidic technologies and biocompatible materials, microphysiological systems (MPS) facilitate the co-culture of human host cells and microbes such as bacteria, fungi, archaea, protozoa, as well as viruses. Therefore, MPS provide the opportunity to study the interaction of host cells and microbiota and unravel underlying mechanisms. A microfluidic intestine-on-chip model was established, which comprised an epithelial and endothelial layer, and monocyte-derived macrophages and DCs. The characterization revealed that monocytes differentiated into CD68++ CX3CR1+ macrophages and CD68+ CD103+ dendritic cells, with a distinct location within the intestinal tissue. Macrophages and DCs demonstrated to be largely unresponsive to luminal LPS administration but elicited a strong inflammatory response after endothelial LPS stimulation. Furthermore, the intestinal model allowed stable colonization with the probiotic strain L. rhamnosus, which is also tolerated by macrophages and DCs, as well as by recruited PBMCs. The intestinal model facilitated microbial interaction studies with the opportunistic pathogen C. albicans. The presence of L. rhamnosus limited the growth of the fungi, reduced tissue damage and translocation into the endothelial layer. The platform allows detailed analysis of host-microbiota interactions and accompanying immune responses. In addition, the model facilitated studying the interplay of commensal bacteria and opportunistic pathogens under physiologically relevant conditions. The intestine-on-chip model proved to be a valuable tool suitable for future investigation of diseases associated with intestinal inflammation
Interactions of Candida albicans with non-pathogenic gut bacteria
No full textThe yeast Candida albicans is a commensal colonizer of mucosal surfaces in humans. Under certain circumstances, the fungus can cause superficial infections like oropharyngeal or vulvovaginal candidiasis, but also invasive and disseminated infections. Predispositions for this opportunistic pathogen to cause disease include antibiotic treatment, immunosuppression, and a compromised epithelial barrier. The intestine is the main reservoir from which the fungus can translocate across the intestinal barrier, invade the bloodstream, and disseminate when predisposing conditions permit. Since intestinal colonization with C. albicans is a prerequisite for infection, research on the fungus in this biological niche is of specific importance to understand the pathogenesis of candidiasis and provide fundamental knowledge for novel therapeutic strategies. As the natural microbiota in the healthy intestine limits fungal overgrowth, this thesis aimed to investigate interactions between C. albicans, intestinal epithelial cells, and intestinal bacteria and to dissect the fungal commensal-to-pathogen shift. Therefore, a static in vitro gut model was established that includes intestinal epithelial cells and mucus-secreting goblet cells, which were colonized with Lactobacillus spp. as a single species artificial microbiota before C. albicans infection. Using this model, Lactobacillus spp. colonization was observed to mediate a time-, dose-, and species-dependent protection against C. albicans pathogenicity. Particularly L. rhamnosus was identified to exhibit a potent protection compared to other tested Lactobacillus species. The bacterial antagonism was related to a reduction of C. albicans cytotoxicity, hypha-length, and translocation. These results were verified in a perfused intestine-on-chip model that contains two compartments separated by a porous membrane to mimic the gut lumen with intestinal epithelial cells and the vasculature with endothelial cells..
Endothelial cell culture in microfluidically perfused biochips enables the recreation of microphysiological conditions of the human vasculature in vitro
No full textThe endothelium lines the inner surface of all blood vessels representing an important tissue with vital functions to mediate tissue homeostasis. Tissue-tissue interfaces play a critical role throughout the human body where endothelial cells (ECs) contribute by creating vital barriers with tight and adherens junctions to regulate permeability of macromolecules and fluids while protecting and nourishing adjacent tissue. They are the most prominent cell type to experience physical forces of shear, stretch and strain through the laminar pulsatile nature of the bloodstream. Alterations in physiological flow profiles have a strong impact on EC pathology contributing to diseases like atherosclerosis and coronary heart disease as well as inflammatory conditions. Further, they are among the first cell types to interact with xenobiotics. Endothelial endocytosis and barrier regulation have profound impact on drug-tissue interactions. There is the need for technological innovations and improvements to study EC biology, EC-epithelial and EC-nanocarrier interactions in more complex settings that take physiological biophysical and biochemical cues into account. For this purpose, the Multi-Organ-Tissue-Flow (MOTiF) biochip has been invented and its design has been finalised during the beginning of this thesis. The objective was to develop handling and cellular seeding protocols for the biochip to establish more in vivo-like and more complex in vitro EC culture approaches. Within the scope of this thesis, the biochip has been characterised for perfused EC culture. Complex co-cultures with tissue resident macrophages and further with murine cortical spheroids present in liver sinusoidal structures and at the blood-brain barrier (BBB) have been established, respectively. Additionally, first applications under physiological parameters of shear stress have been made. The focus was on nanocarrier uptake profiles and microvascular endothelial barrier interaction
Molecular Morphology: Phylogenetically Informative Characters Derived from Sequence Data
No full textA fundamental problem in biology is the reconstruction of the relatedness of all (extant) species.
Traditionally, systematists employ visually recognizable characters of organisms for classification and evolutionary analysis. Recent developments in molecular and computational biology, however, lead to a whole different perspective on how to address the problem of inferring relatedness. The discovery of molecules, carrying genetic information, and the comparison of their primary structure has, in a rather short period of time, revolutionized our understanding of the phylogenetic relationship of many organisms.
These novel approaches, however, turned out to bear similar problems as previous techniques. Moreover, they created new ones. Hence, taxonomists came to realize that even with this new type of data not all problematic relationships could be unambiguously resolved. The search for complementary approaches has led to the utilization of rare genomic changes and other characters which are largely independent from the primary structure of the underlying sequence(s). These “higher order” characters are thought to be evolutionary conserved in certain lineages and largely unaffected by primary sequence data-based problems, allowing for a better resolution of the Tree of Life.
The central aim of this thesis is the utilization of molecular characters of higher order in connection with their consistent and comparable extraction from a given data set. Two novel methods are presented that allow such an inference. This is complemented with the search for and analysis of known and novel molecular characteristics to study the relationships among Metazoa, both intra- as well as interspecific.
The first method tackles a common problem in phylogenetic analyses: the inference of reliable data set. As part of this thesis a pipeline was created for the automated annotation of metazoan mitochondrial genomes. Data thus obtained constitutes a reliable and standardized starting point for all downstream analyses, e.g. genome rearrangement studies.
The second method utilizes a subclass of gaps, namely those which define an approximate split of a given data set. The definition and inference of such split-inducing indels (splids) is based on two basic principles. First, indels at the same position, i.e. sharing the same end points in two sequences, are likely homologous. Second, independent single-residue insertions and deletions tend to occur more frequently than multi-residue indels. It is shown that trees based on splids recover most of the undisputed monophyletic groups while influence of the underlying alignment algorithm is relatively small.
Mitochondrial markers are a valuable tool for the understanding of small and large scale population structure. The non-coding control region of mitochondrial DNA (mtDNA) often contains a higher amount of variability compared to genes encoding proteins and non-coding RNAs. A case study on a small scale population structure investigates the control region of the European Fire-bellied Toad in order to find highly variable parts which are of potential importance to develop informative genetic markers. A particular focus is placed on the investigation of the evolutionary dynamics of the repetitive region at an inter- and intraspecific level. This includes understanding mechanisms underlying its evolution, i.e. by exploring the impact of secondary structure on slipped strand mispairing during mtDNA replication.
The 7SK RNA is a key player in the regulation of polymerase II (Pol-II) transcription, interacting with at least three known proteins: It mediates the inhibition of the Positive Transcription Elongation Factor b (P-TEFb) by the HEXIM1/2 proteins, thereby repressing transcript elongation by Pol-II. A highly specific interaction with LARP7 (La-Related Protein 7), on the other hand, regulates its stability. 7SK RNA is capped at its 5’ end by a highly specific methyltransferase MePCE (Methylphosphate Capping Enzyme). Employing sequence and structure similarity it is shown that the 7SK RNA as well as its protein binding partners have a much earlier evolutionary origin than previously expected. Furthermore, this study presents a good illustration of the pitfalls of using markers of higher order for phylogenetic inference
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