Preview

PDF, English - main document Download (4MB) | Terms of use

Abstract

Listeria monocytogenes (Lm) is an opportunistic, facultatively intracellular pathogen that enters the host via contaminated food, causing listeriosis. Given opportunity, Lm can enter the bloodstream by penetrating the gut barrier, reach the liver and the spleen and persist in them. Rarely, it can also invade the fetus in pregnant women or the central nervous system (CNS), namely brain, causing a serious condition characterized by a very high mortality rate and lasting neurological problems in survivors.

Direct penetration into cells in general is mediated by binding of listerial surface virulence factors (VFs) – primarily those belonging to internalin family – to specific cellular receptors, leading to uptake by zipper-type endocytosis, even in non-phagocytic cells. The best-known receptors exploited by Lm in this manner are adherens junction protein E-cadherin (Ecad) and receptor tyrosine kinase (RTK) Met – Ecad is bound by internalin (InlA) and Met is bound by internalin B (InlB). There are two barriers through which Lm can pass to enter the brain: blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (BCSFB). The exact mechanisms of entry into the brain remain elusive, with research mostly focusing on interactions between listerial VFs and their binding partners, e.g. InlA and Ecad, InlB and Met (and its co-receptor CD44v6) or internalin F (InlF) and vimentin.

The investigation of host cell response during infection by Lm was done in in vitro models of the BBB and the BCSFB, chiefly in human brain microvascular endothelial cells (HBMEC) for the BBB and human choroid plexus papilloma (HIBCPP) cells for the BCSFB. Part of the in vitro experiments aimed to reproduce the findings from other cell lines in HBMEC and/or HIBCPP cells (e.g. effects of MAPK, dynamin and vimentin inhibition as well as deletion of InlA, InlB and/or InlF on bacterial invasion rates). The other part of in vitro experiments consisted of an analysis of the effects of CD44v6-blocking peptides on bacterial invasion rates, as well as the investigation into involvement of various RTKs other than Met in listerial invasion. Finally, a series of infection experiments with mice was performed, with an aim to deduce the dependence of the successful development of systemic, orally acquired listeriosis on immunosuppression and CD44v6-Met InlB interactions.

The results presented within this study outline a) the potentially InlF-independent role of vimentin and b) possible involvement of multiple previously unreported RTKs in listerial invasion, as well as c) importance of immunosuppression for efficient chronic infection of mice. No effect of CD44v6 blocking peptides on either the bacterial invasion into different cell lines or the development of systemic infection in mice was observed during the experiments, and more investigative effort is necessary to elucidate the question further.