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Erkennung von Staphylococcus-aureus-Zellwandkomponenten durch das angeborene Immunsystem : strukturelle und funktionelle Voraussetzungen

Erkennung von Staphylococcus-aureus-Zellwandkomponenten durch das angeborene Immunsystem : strukturelle und funktionelle Voraussetzungen

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SIGEL, Stefanie, 2009. Erkennung von Staphylococcus-aureus-Zellwandkomponenten durch das angeborene Immunsystem : strukturelle und funktionelle Voraussetzungen [Dissertation]. Konstanz: University of Konstanz

@phdthesis{Sigel2009Erken-7568, title={Erkennung von Staphylococcus-aureus-Zellwandkomponenten durch das angeborene Immunsystem : strukturelle und funktionelle Voraussetzungen}, year={2009}, author={Sigel, Stefanie}, address={Konstanz}, school={Universität Konstanz} }

application/pdf Sigel, Stefanie Staphylococcus aureus (S. aureus), a frequent human pathogen, often colonizes humans asymptomatically but can also establish severe infections of tissue or spread to the blood, leading to sepsis and sometimes death. Upon infection, the bacteria are recognized by specific immune receptors of the host able to bind to different molecular patterns of S. aureus, thereby inducing anti-bacterial responses, such as inflammation. Innate immune activation by S. aureus strongly depends on Toll like receptor (TLR) 2, which, beside other staphylococcal cell wall components, recognizes lipoteichoic acid (LTA), a major immunostimulatory molecule of all Gram positive bacteria. Despite the prominent role of LTA in S. aureus mediated immune activation, purified LTA selectively fails to initiate the release of IL 12 and subsequent IFNy in human whole blood. In contrast, stimulation of blood cells with whole S. aureus results in a strong IFNy release, suggesting further staphylococcal components to be responsible for its production. In the first part of this thesis, the IFNy inducing principle of S. aureus cell walls was characterized.<br />- Stimulation of human whole blood with staphylococcal cell wall preparations revealed that S. aureus triggers IFNy production in NK cells and T cells in a TNF and IL-12 dependent manner. IFNy release was found to be sensitive to phagocytosis inhibition and to treatment with enzymes digesting peptidoglycan (PGN), pointing to an important role of ingested PGN in S. aureus induced IFNy production. However, knock-out mice deficient in TLR2 or Nod2, both considered essential PGN receptors, did not show significantly altered IFNy release upon stimulation with S. aureus cell wall preparations. The experiments indicate that not S. aureus PGN itself represents a major IFNy inducing component but that it amplifies the recognition of PGN associated immunostimulatory molecules by mediating their intracellular uptake or presentation to the respective immune receptors.<br />Despite the pivotal role of LTA in S. aureus-mediated immune activation, soluble LTA has been described to be a weak inducer of inflammatory responses in vivo. Furthermore, soluble LTA released from the staphylococcal membrane was found to interact with human serum components, which might influence its recognition by innate immune receptors. In the second part of this PhD thesis LTA binding proteins were identified from human serum and their influence on LTA mediated cytokine secretion was investigated.<br />- SDS-PAGE profiles of human serum proteins, fractionated by gel chromatography in the presence or absence of S. aureus derived LTA, revealed interactions between LTA and different apolipoproteins. Among these apolipoproteins, significant inhibition of LTA-induced cytokine release was demonstrated for Apo B100 and could be mirrored by incubation of soluble LTA with human serum prior to stimulation of human blood cells.<br />Despite strong evidence that LTA represents a major immunostimulatory principle of Gram positive bacteria, recent reports suggested that not LTA but lipoproteins are dominant immunobiologically active structures of S. aureus and that the activity of purified LTA lies in contaminating lipoproteins. This was concluded from a 100 fold decreased immunostimulatory capacity of LTA preparations from mutant S. aureus lacking palmitate labeled lipoproteins (lgt) compared to LTA from the respective wild type strain (wt). In contrast, using the same bacterial strains and comparable experimental systems, i.e. human whole blood, we were able to demonstrate equipotent cytokine induction between lgt LTA and wt LTA. In order to find an explanation for these discrepancies in lgt LTA mediated immune activation, the specific requirements for lgt LTA recognition were investigated in the last part of this thesis.<br />- Cytokine induction by lgt LTA in human whole blood was critically dependent on LTA immobilization, phagocytic activity of blood cells and the presence of human serum, whereas wt LTA showed only an incomplete dependency. Furthermore, lgt LTA induced immune activation was strongly augmented by LTA specific IgG antibodies found to be present in human sera at varying levels. These results suggest a novel mechanism for lgt LTA mediated immune activation in human blood cells that involves opsonization dependent uptake of LTA enabling intracellular recognition and further explain why a previous study was unable to detect lgt LTA induced immune activation. Sigel, Stefanie 2011-05-04T10:02:09Z 2009 Erkennung von Staphylococcus-aureus-Zellwandkomponenten durch das angeborene Immunsystem : strukturelle und funktionelle Voraussetzungen deposit-license eng

Dateiabrufe seit 01.10.2014 (Informationen über die Zugriffsstatistik)

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