Ziewer, Sebastian: Pattern Recognition Receptor and Vaccination Studies in the Murine Model of Lymphatic Filariasis. - Bonn, 2013. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5n-31327
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5n-31327,
author = {{Sebastian Ziewer}},
title = {Pattern Recognition Receptor and Vaccination Studies in the Murine Model of Lymphatic Filariasis},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2013,
month = mar,

note = {Lymphatic filariasis is a parasitic helminth infection that affects approximately 120 million people. About one third of the infected individuals develop pathological manifestations, e.g. lymphedema. Causative agents of lymphatic filariasis are filarial nematodes, which are transmitted during the blood meal of mosquitoes. Filarial worms contain endosymbiotic bacteria of the genus Wolbachia, which are an additional stimulus for the host’s immune system and have been intensively discussed to promote pathology due to an exacerbated proinflammatory response of the host. Currently, the available treatment used for mass treatment against filariasis is based on chemotherapeutic intervention that reduces the burden of the blood circulating larval stages but has only limited effects on adult worms. Despite major attempts to eradicate filarial diseases, elimination has not been achieved. Also, with resistance against the chemotherapy being observed and high cost and logistics efforts of mass drug administration, a vaccine would be a desirable tool towards the elimination of the disease. However, despite intensive research there are no vaccines against any human filarial infection.
Pattern recognition receptors (PRRs) are able to sense structures of pathogens, such as viruses or bacteria. In order to investigate, how Wolbachia may induce such proinflammatory immune responses, the PRRs TLR2, TLR4 and NOD2 were investigated, since they are known to sense bacterial structures. In the first part of this thesis in vitro experiments revealed that proinflammatory responses, measured by the secretion of TNF and IL-6, were induced after in vitro stimulation of antigen-presenting cells with filarial Litomosoides sigmodontis extract. In contrast, L. sigmodontis extract devoid of Wolbachia did not induce the secretion of TNF and IL-6. The recognition of Wolbachia was transduced by the heterodimer TLR2/6 (but not TLR1/2 or TLR4) and the integration of the intracellular adapter molecule MyD88 was mandatory. In contrast, the intracellular receptor NOD2, which is known for his interaction with TLR2, was not necessary for this proinflammatory response. In addition to the in vitro experiments, it was of interest, whether mice deficient for these receptors show an altered course of infection to demonstrate the in vivo importance of these PRRs in filarial infections. While the parasite burden after L. sigmodontis infection was similar between TLR-, MyD88-deficient and the corresponding receptor-competent mice, NOD2-deficient mice showed a higher worm load. In addition, the worms recovered from NOD2-deficient mice were shorter and showed an impaired development. Taken together, these data show that despite the induction of proinflammatory responses, TLR-2 and MyD88 do not influence the infection in vivo. In contrast, the higher worm burden observed in NOD2-deficient mice indicates a role for this PRR in the defense against filarial parasites. Further investigations are needed to identify the molecular mechanism behind these observations.
In the second part of this thesis a successful vaccination against the L. sigmodontis microfilarial stage was established. The vaccination presented in the present thesis was performed by subcutaneous injection of microfilariae together with adjuvant alum and led to a strongly reduced microfilarial burden in the blood and at the site of infection. Analysis of filarial embryogenesis revealed that the development of microfilariae was already impaired in the uteri of female worms. The vaccination caused a switch from the Th2 arm of immunity, which is well-known for filarial infections, towards a Th1 milieu, indicated by increased IFN-γ and IgG2 in immunized mice. The results of these experiments not only contribute to the understanding of the immune mechanisms needed to develop a vaccine against filarial parasites, but moreover raise hope for the development of a human vaccination against the transmission stage of lymphatic filariasis.},

url = {http://hdl.handle.net/20.500.11811/5633}

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