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This thesis contains results from transcriptome studies on different aspects of host-pathogen interactions. First, liver gene expression profiles from a murine chronic stress model served to elucidate aspects of the influence of stress on metabolism and immune response state. Chronic stress in female BALB/c mice was shown to lead to a hypermetabolic syndrome including induction of gluconeogenesis, hypercholesteremia, and loss of essential amino acids, to the induction of the acute phase response, but also of immune suppressive pathways and to the repression of hepatic antigen presentation. Increased leukocyte trafficking, increased oxidative stress together with counter-regulatory gene expression changes, and an induction of apoptosis were detected. The influence of intra-venous infection on the host kidney gene expression was analyzed in another murine model using the wild type strain Staphylococcus aureus RN1HG and its isogenic sigB mutant. Gene expression profiling indicated a highly reproducible host kidney response to infection. The comparison of infected with non-infected samples revealed a strong inflammatory reaction of kidney tissue, e. g. Toll-like receptor signaling, complement system, antigen presentation, interferon and IL-6 signaling. However, the results of this study did not provide any hints for differences in the pathomechanism of the S. aureus strains RN1HG and ΔsigB, since the host response did not differ between infections with the two strains analyzed. Effects of SigB might be transient, only apparent at earlier time points, or might also be compensated for in the in vivo infection by the interlaced pattern of other regulators. SigB might possess only to a lesser extent characteristics attributed to virulence factors and might act in vivo more like a virulence modulator and fine tune bacterial reactions. In addition to the analysis of tissue samples, different in vitro models were furthermore studied. The third part of this thesis focuses on bone-marrow derived macrophages (BMM) of the two mouse strains BALB/c and C57BL/6, which are described in literature to exhibit genetically determined differences in their reaction to infection. Expression profiling was performed on control and IFN-γ treated samples from a serum-free cultivation system and revealed mainly induction of gene expression after treatment of BMM with IFN-γ. Gene expression changes confirmed known IFN-γ effects like induction of immunoproteasome, antigen presentation, interferon signaling related genes, GTPase/GBPs, and inducible NO synthase. IFN-γ dependent gene expression changes were highly similar in BALB/c and C57BL/6 BMM. Considering gene expression differences between BMM of both strains, a similar expression trend was visible on the level of untreated controls as well as after IFN-γ treatment. Differentially expressed genes between BMM of both strains included immune-relevant genes as well as genes linked to cell death, but the coverage of functional groups was limited. The bronchial epithelial cell line S9 was used as an in vitro model system for the infection with S. aureus RN1HG. The fourth chapter in this thesis includes S9 cell gene expression signatures 2.5 h and 6.5 h after start of infection. At the early time point, only 40 genes were differentially expressed, which nevertheless indicated a beginning pro-inflammatory response, e. g. induction of cytokines (IL-6, IFN-β, LIF) or prostaglandin-endoperoxide synthase 2 (PTGS2), but also counter-regulatory processes, e. g. induction of CD274. The host cell response was dramatically aggravated at the later 6.5 h time point. Differential expression was detected for 1196 genes. These included induced cytokines, pattern recognition receptor signaling, antigen presentation, and genes involved in immune defense (e. g. GBPs, MX, APOL). Negative effects on growth and proliferation were even more enhanced in comparison to the early time point, and signs for apoptotic processes were revealed. Finally, the last chapter addresses amongst others the pathogen’s expression profile in the S9 cell in vitro infection model at the two time points 2.5 h and 6.5 h after start of infection by tiling array gene expression analysis. The pathogen expression profiling revealed the activity of the SaeRS two-component system in internalized staphylococci. Partly dependent on SaeRS, the induction of adhesins (e. g. fnbAB, clfAB), toxins (hlgBC, lukDE, hla), and immune evasion genes (e. g. chp, eap) was observed. Furthermore, expression changes of metabolic genes were recorded (gene induction of amino acid biosynthesis, TCA cycle, gluconeogenesis; gene repression of glycolysis, purine biosynthesis, tRNA synthetases). Expression analysis recorded a distinct bacterial expression program, which supported literature results of a specific, bacterial strain and host cell line dependent transcriptional adaptation of the pathogen.
Nach Schlaganfall werden infolge einer einsetzenden Immunsuppression häufig Sekundärinfektionen beobachtet. Diese beeinflussen das Outcome und die Mortalität der Patienten bedeutend. In der vorliegenden Arbeit wurden als Mechanismen der angeborenen Immunantwort die Migration, Phagozytose und NETose neutrophiler Granulozyten und Monozyten untersucht, um mögliche Einschränkungen infolge der Immunsuppression zu erkennen. Dafür wurden Leukozyten von Schlaganfallpatienten mit denen gesunder Probanden verglichen. Während Migration und Phagozytose nach Schlaganfall unbeeinträchtigt waren, zeigten sich für die mittlere NET-Fläche am Tag 1 nach Schlaganfall deutlich reduzierte Werte nach Stimulation mit fMLP und PMA im Vergleich zu gesunden Kontrollen. Dieser Effekt verlor sich in der ersten Woche nach Schlaganfall. In der reduzierten NET-Fläche kann eine mögliche Ursache für das Auftreten von Sekundärinfektionen gesehen werden.
Herpesviruses are enveloped DNA viruses which are dependent on two fusion steps for efficient replication in the host cell. First, they have to fuse their envelope with the cellular plasma membrane or with the vesicle membrane after endocytic uptake to enter the host cell and second, they have to export the newly generated nucleocapsids from the site of assembly to the cytoplasm by fusion of the primary virion envelope with the outer nuclear membrane (ONM). The main goal of this project was to provide a better understanding of how herpesvirus capsids exit the nucleus. On the one hand this thesis aimed at finding cellular proteins involved in nuclear egress (Paper I), while on the other the focus was on further characterization of the viral nuclear egress complex (NEC, Paper II) and its interaction with the capsid (Paper III).
It is the hallmark of viruses, including herpesviruses, to hijack host cell proteins for their efficient replication. Some of those interactions are well characterized, while others might not yet have been discovered. In the last step of the nuclear egress, where the primary virion membrane fuses with the ONM, most likely a cellular machinery is involved. The presented work focused on Torsin, the only known AAA+ ATPase localizing in the endoplasmic reticulum and the perinuclear space (PNS). For this, the effect of overexpression of WT and mutant proteins, as well as CRISPR/Cas9 generated knock-out cell lines, on PrV replication was analyzed. Neither single overexpression nor single knockouts of TorA or TorB had any significant effects on virus titers. However, infection of TorA/B double knockout cells revealed reduced viral titers and an accumulation of primary virions in the PNS at early infection times, indicating a delay in nuclear egress.
The process of nuclear egress has been intensively investigated without revealing all its details. To address some of the missing aspects we generated monoclonal antibodies (mAbs) against the NEC and its components (pUL31 and pUL34) for a better visualization of the process in transfected as well as infected cells. These mAbs provide a useful tool for future analyses.
The publication of the NEC crystal structure formed the basis for intensive research on the molecular details of the NEC formation and its interaction with the nucleocapsid. Recently, our lab showed that lysine (K) at position 242 in the membrane-distal part of pUL31 is crucial for incorporation of the nucleocapsid into budding vesicles. Replacing K by alanine (A) resulted in accumulations of vesicles in the PNS, while mature capsids were not incorporated. To test whether this is due to electrostatic interference or structural restrictions we substituted K242 by different aa to determine the requirements for nucleocapsid uptake into the nascent primary particles. To analyze whether the defect of pUL31-K242A can be compensated by second-site mutations, PrV-UL31-K242A was passaged and mutations in revertants were analyzed. Different mutations have been identified compensating for the K242A defect. A considerable number of mutations indicates that the NEC is much more flexible than previously thought. Further, we gained information that the K at position 242 is not directly involved in capsid interaction, while it is more likely involved in rearrangements within the NEC coat.
Group A streptococcus (GAS) and Streptococcus pneumoniae are both Gram-positive bacteria that asymptomatically colonise various human body parts. Both microbes cause diseases ranging from mild to severe invasive infections. The later are associated with high mortality. GAS is the major microbial aetiology of type II necrotising skin and soft tissue infections (NSTIs). Type II NSTIs typically affect the lower and upper limbs of healthy young adults and often require debridement as a surgical intervention to prevent the spread of infection. S. pneumoniae is the major cause of respiratory tract infections including community-acquired pneumonia in young children and the elderly. Although most respiratory tract infections are successfully treated with antibiotics, emerging antibiotic resistance is a major cause of concern. Secreted virulence factors of Gram-positive bacteria play a major role in the successful invasion of host tissues causing different diseases. Additionally, they facilitate the spread of infection, contribute to tissue pathology, and potentially act as immune evasion mechanisms. This thesis summarises the consequences of streptococcal pyrogenic exotoxin B (SpeB), a potent cysteine protease secreted by GAS and pneumococci-derived hydrogen peroxide (H2O2) on host responses.
GAS have developed genetic or phenotypic ways of adapting to the immune response to escape immune clearance. Analysis of GAS clones recovered from NSTI patient biopsies exhibit a mixed SpeB phenotype, with most clones being SpeB negative. SpeB negative clones have been associated with hyper-virulence. In Paper II, we showed that SpeB negative GAS clones recovered from tissue exhibit reversible impaired SpeB secretion due to environmental factors. In addition, mutations in covS and ropB, the major transcriptional regulators of SpeB expression, were responsible for the irreversible loss of SpeB expression. Immunohistochemistry analysis demonstrated that neutrophil degranulation, necrosis and excessive inflammation observed in NSTIs patient biopsies correlated with bacterial load and SpeB negativity of clones. Proteomic data analysis showed that SpeB negative GAS recovered from neutrophil infection harboured the protease intracellularly suggesting that the bacteria expressed but did not secrete SpeB. We have also shown that neutrophil-derived reactive oxygen species, H2O2 and hypochlorous acid, drive the SpeB negative phenotype. The SpeB negative clones survived neutrophil-mediated antimicrobial killing and induced excessive degranulation when compared with SpeB positive clones. These results provide new insights into GAS fitness induced by host factors in tissue and may be useful for the development of new treatment strategies in NSTIs.
Pneumococci produce H2O2 as a by-product of carbohydrate metabolism in a reaction catalysed by pyruvate oxidase SpxB. However, very little is known about the effects of pneumococcal H2O2 as a virulence factor. Our study aimed to investigate the role of H2O2 in initiating epithelial cell death, focusing on apoptosis and pyroptosis. In Paper III, we showed that pneumococci-derived H2O2 caused epithelial cell cytotoxicity by priming and activating the NLRP3 inflammasome resulting in subsequent IL-1β production and release. Additionally, H2O2 caused apoptotic and pyroptotic cell death as evidenced by activation of caspase-3/7 and caspase-1, respectively. However, the release of IL-1β was dependent on apoptosis and not pyroptosis since inactive gasdermin D was detected post-infection. These observations were not detected in the absence of H2O2. Overall, we showed the damaging effects of pneumococci-derived H2O2 on human bronchial epithelial cells.