Macrophages are key cells of the innate immune system. By capturing and ingesting microbes in a process known as phagocytosis, they play an important role in defending host tissues against infection. There are two types of macrophage: tissue-resident macrophages, and bone marrow monocytes that circulate in the bloodstream and are recruited in tissues during infection where they become macrophages. Tissue-resident macrophages differ from monocyte-derived macrophages in terms of their origins, development and role.
Scientists from the Institut Pasteur, Inserm and Paris Descartes – Sorbonne Paris Cité University (Biology of Infections Unit, Inserm U1117, directed by Marc Lecuit) have demonstrated that liver-resident macrophages are rapidly killed by the pathogenic bacterium Listeria monocytogenes. This early death triggers the recruitment of macrophages from the bloodstream to the liver. These macrophages start by bringing the bacterial infection under control; then, in an unexpected development, they actually replace the liver-resident macrophages that have been killed by the infection.
This previously unknown mechanism sheds light on the way in which an organ such as the liver is able to control a bacterial infection and return to homeostasis once the pathogen has been eliminated. In immunological terms, this research also reveals a new functional interconnection between resident and recruited macrophages.
Illustration: Hepatic macrophage (in green) ingesting by phagocytosis pathogenic bacterium Listeria monocytogenes (in red). © Institut Pasteur
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Liver-Resident Macrophage Necroptosis Orchestrates Type 1 Microbicidal Inflammation and Type-2-Mediated Tissue Repair during Bacterial Infection, Immunity, 07 Janvier 2015http://dx.doi.org/10.1016/j.immuni.2014.12.020
Camille Blériot (1,2), Théo Dupuis (1,2), Grégory Jouvion (3), Gérard Eberl (4), Olivier Disson (1,2), Marc Lecuit (1,2,5,6,*)
(1) Institut Pasteur, Biology of Infection Unit, 75015 Paris, France
(2) Inserm U1117, 75015 Paris, France
(3) Institut Pasteur, Human Histopathology and Animal Models Unit, 75015 Paris, France
(4) Institut Pasteur, Lymphoid Tissue Development Unit, 75015 Paris, France
(5) Institut Pasteur, French National Reference Center and World Health Organization Collaborating Centre on Listeria, 75015 Paris, France
(6) Paris Descartes University, Sorbonne Paris Cité, Institut Imagine, Division of Infectious Diseases and Tropical Medicine, Necker-Pasteur Centre for Infectiology, Necker-Enfants Malades University Hospital, 75015 Paris, France
* Corresponding Author