Eosinophil Extracellular DNA Trap Cell Death (EETosis) occurs as a life-cycle stage-specific response to filariae

Abstract

Filarial nematodes represent a great burden of human morbidity causing diseases like onchocerciasis and lymphatic filariasis. The lack of a vaccination and a short-term therapy with a macrofilaricidal effect hampers the elimination of filarial diseases. To successfully eliminate filariasis, not only new therapies, but also a detailed knowledge of protective immunity is needed. Helminths typically induce a type 2 immune response in their host with a profound eosinophilia. Eosinophils are a pivotal cell type in controlling helminth infections and are of particular importance in eliminating microfilariae (MF), the progeny of the filariae. Next to the release of cytotoxic granules, a newly recognized defense mechanism of granulocytes is the so called extracellular DNA trap cell death (ETosis), which results in the release of intracellular DNA into the surrounding. <br /> The results show for the first time that bone marrow-derived eosinophils as well as eosinophils isolated from infected animals are able to produce eosinophil extracellular DNA traps (EETs) of nuclear and primarily of mitochondrial origin in response to <em>Litomosoides sigmodontis</em> MF and inhibit MF motility in a DNA-trap- and cell contact-dependent manner <em>in vitro</em>. MF-induced ETosis was not based on shear forces, independent on antibody-coating and required no prior priming. Within this thesis the dectin-1 receptor was identified as the underlying receptor in MF-induced ETosis. Results from this thesis further suggest the DNA-dependent inhibition of MF motility and MF-induced DNA release by eosinophils as a conserved mechanism, since murine eosinophils responded to MF derived from the rodent filarial nematode <em>L. sigmodontis</em> and the canine heartworm Dirofilaria immitis. <em>In vivo</em> results showed an increase in local DNA concentration upon <em>L. sigmodontis</em> infection and raised systemic DNA concentrations upon intravenous MF injection, which was partly mediated by eosinophils, indicating a potential role of EETosis <em>in vivo</em> as well.<br/> Furthermore, several pre-clinical studies using the <em>L. sigmodontis</em> rodent model were conducted identifying new macrofilaricidal drug candidates against human filariasis.<br/> In conclusion, the results of this thesis show for the first time that murine EETosis occurs in response to filariae and identifies the dectin-1 receptor-recognition being responsible for the MF-induced ETosis. Furthermore, the results contribute to the knowledge about eosinophil-mediated protective immunity and show that EETosis occurs as a universal and conserved mechanism against a variety of pathogens. Finally, new potential drug candidates were tested, which present promising candidates for the elimination of human filariasis.