Microbes and Infection 15 (2013) 971e980 www.elsevier.com/locate/micinf
In vitro and in vivo models to study human listeriosis: mind the gap Olivier Disson a,b, Marc Lecuit a,b,c,d,* a
Institut Pasteur, Biology of Infection Unit, 75015 Paris, France b Inserm U1117, 75015 Paris, France c Institut Pasteur, French National Reference Center and World Health Organization Collaborating Centre Listeria , 75015 Paris, France d Paris Descartes University, Sorbonne Paris Cite´, Institut Imagine, Department of Infectious Diseases and Tropical Medicine, Necker-Pasteur Centre for Infectiology, Necker-Enfants Malades University Hospital, 75015 Paris, France Received 2 August 2013; accepted 26 September 2013 Available online 18 October 2013
Abstract Listeria monocytogenes (Lm) is the etiological agent of listeriosis, one of the deadliest human foodborne infections. Lm is able to cross the intestinal, placental and bloodebrain barriers, leading to septicemia, fetoplacental infection, meningitis and encephalitis. The intracellular life cycle of this facultative intracellular bacterium has been studied in detail in in vitro cell culture systems. Lm enters in non-phagocytic cells in an InlAeEcad and/or InB-Met dependent manner. Lm then escapes from its internalization vacuole via the action of the pore forming toxin LLO and spreads from cell to cell in an ActA-dependent manner. In vivo studies in “humanized” mouse models and human epidemiological data have led to the deciphering of the mechanisms underlying Lm crossing of intestinal and placental barriers. As illustrated in this review, in vivo outcomes could not be deduced directly from in vitro observations, and led to revisit the intracellular fate of Lm during infection. Ó 2013 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved. Keywords: Listeriosis; Listeria monocytogenes; In vivo; In vitro; Animal model
1. Introduction The Gram-positive bacterium Listeria monocytogenes (Lm) is the etiological agent of listeriosis, a deadly foodborne infection. This facultative intracellular bacterium crosses the intestinal barrier and may disseminate systemically and breach other host barriers such as the placental and bloodebrain barriers, leading to maternalefetal infections and meningitis or encephalitis [1,67]. This bacterium has been used as a powerful tool to study innate and adaptive immune responses in mouse models [2,3]. The use of Lm as a model microorganism to study the cell biology of infection using in vitro cultured cell lines has led to major breakthroughs since the middle of the 80’s [4]. One of the most striking properties of Lm is its ability to enter in non-phagocytic cells via the action
* Corresponding author. Biology of Infection Unit, Institut Pasteur, Inserm U1117, 75015 Paris, France. Tel.: þ33 140 613 420; fax: þ33 140 613 421. E-mail addresses: [email protected], [email protected] (M. Lecuit).
of two of its surface proteins called internalin (InlA) and InlB. In in vitro-infected non-phagocytic cells as well as in phagocytic cells, Lm may escape from the vacuole in a listeriolysin O (LLO)-dependent manner and spread from cell to cell by polymerizing actin in an ActA-dependent manner. Comparative genomics between Lm and the non-invasive non-pathogenic Listeria innocua [5] allowed uncovering new putative genes involved in virulence that have been studied in welldefined in vitro models and tested in vivo. They include, among other factors, a bile salt hydrolase (BSH) [6], surface proteins Auto and Vip involved in entry [7,8] and members of the internalin family [9]. Current challenges are to understand how Lm actually interacts with host cells in the complex in vivo setting, and to dissect hostepathogen interactions in living tissues at the cellular level as precisely as in reductionist in vitro systems. Such studies will lead to a precise understanding of the biology of listeriosis, and may also reveal new infection strategies and enrich our understanding of cell, tissue and host responses to infection.
1286-4579/$ - see front matter Ó 2013 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.micinf.2013.09.012
972
O. Disson, M. Lecuit / Microbes and Infection 15 (2013) 971e980
2. Intracellular life cycle of L. monocytogenes, lessons from in vitro studies The intracellular life cycle of Lm has been thoroughly studied in vitro (Fig. 1, see for detailed review [10]). Most of the proteins involved in cell entry and intracellular survival are regulated by the transcriptional activator PrfA [11]. PrfA is activated by several environmental factors, including temperature. A so called thermoswitch is situated in the 50 UTR of the prfA transcript: it hides the ribosome binding site at temperatures
In vitro and in vivo models to study human listeriosis: mind the gap Olivier Disson a,b, Marc Lecuit a,b,c,d,* a
Institut Pasteur, Biology of Infection Unit, 75015 Paris, France b Inserm U1117, 75015 Paris, France c Institut Pasteur, French National Reference Center and World Health Organization Collaborating Centre Listeria , 75015 Paris, France d Paris Descartes University, Sorbonne Paris Cite´, Institut Imagine, Department of Infectious Diseases and Tropical Medicine, Necker-Pasteur Centre for Infectiology, Necker-Enfants Malades University Hospital, 75015 Paris, France Received 2 August 2013; accepted 26 September 2013 Available online 18 October 2013
Abstract Listeria monocytogenes (Lm) is the etiological agent of listeriosis, one of the deadliest human foodborne infections. Lm is able to cross the intestinal, placental and bloodebrain barriers, leading to septicemia, fetoplacental infection, meningitis and encephalitis. The intracellular life cycle of this facultative intracellular bacterium has been studied in detail in in vitro cell culture systems. Lm enters in non-phagocytic cells in an InlAeEcad and/or InB-Met dependent manner. Lm then escapes from its internalization vacuole via the action of the pore forming toxin LLO and spreads from cell to cell in an ActA-dependent manner. In vivo studies in “humanized” mouse models and human epidemiological data have led to the deciphering of the mechanisms underlying Lm crossing of intestinal and placental barriers. As illustrated in this review, in vivo outcomes could not be deduced directly from in vitro observations, and led to revisit the intracellular fate of Lm during infection. Ó 2013 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved. Keywords: Listeriosis; Listeria monocytogenes; In vivo; In vitro; Animal model
1. Introduction The Gram-positive bacterium Listeria monocytogenes (Lm) is the etiological agent of listeriosis, a deadly foodborne infection. This facultative intracellular bacterium crosses the intestinal barrier and may disseminate systemically and breach other host barriers such as the placental and bloodebrain barriers, leading to maternalefetal infections and meningitis or encephalitis [1,67]. This bacterium has been used as a powerful tool to study innate and adaptive immune responses in mouse models [2,3]. The use of Lm as a model microorganism to study the cell biology of infection using in vitro cultured cell lines has led to major breakthroughs since the middle of the 80’s [4]. One of the most striking properties of Lm is its ability to enter in non-phagocytic cells via the action
* Corresponding author. Biology of Infection Unit, Institut Pasteur, Inserm U1117, 75015 Paris, France. Tel.: þ33 140 613 420; fax: þ33 140 613 421. E-mail addresses: [email protected], [email protected] (M. Lecuit).
of two of its surface proteins called internalin (InlA) and InlB. In in vitro-infected non-phagocytic cells as well as in phagocytic cells, Lm may escape from the vacuole in a listeriolysin O (LLO)-dependent manner and spread from cell to cell by polymerizing actin in an ActA-dependent manner. Comparative genomics between Lm and the non-invasive non-pathogenic Listeria innocua [5] allowed uncovering new putative genes involved in virulence that have been studied in welldefined in vitro models and tested in vivo. They include, among other factors, a bile salt hydrolase (BSH) [6], surface proteins Auto and Vip involved in entry [7,8] and members of the internalin family [9]. Current challenges are to understand how Lm actually interacts with host cells in the complex in vivo setting, and to dissect hostepathogen interactions in living tissues at the cellular level as precisely as in reductionist in vitro systems. Such studies will lead to a precise understanding of the biology of listeriosis, and may also reveal new infection strategies and enrich our understanding of cell, tissue and host responses to infection.
1286-4579/$ - see front matter Ó 2013 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.micinf.2013.09.012
972
O. Disson, M. Lecuit / Microbes and Infection 15 (2013) 971e980
2. Intracellular life cycle of L. monocytogenes, lessons from in vitro studies The intracellular life cycle of Lm has been thoroughly studied in vitro (Fig. 1, see for detailed review [10]). Most of the proteins involved in cell entry and intracellular survival are regulated by the transcriptional activator PrfA [11]. PrfA is activated by several environmental factors, including temperature. A so called thermoswitch is situated in the 50 UTR of the prfA transcript: it hides the ribosome binding site at temperatures
