Legionellosis: A novel mechanism by which the bacterium Legionella
pneumophila regulates the immune response of its host cells

Date:
February 18, 2022
Source:
Institut Pasteur
Summary:
Legionellosis or Legionnaires' disease affected more than 1 800
people in France in 2019 and caused 160 deaths. This emerging
disease is caused by Legionella pneumophila, an environmental
bacterium that thrives in hot water systems. Researchers have
discovered a mechanism that allows Legionella pneumophila to target
the immune response of the cells it infects by secreting a small
regulatory RNA. This mechanism, not described before, facilitates
the survival and proliferation of Legionella pneumophila during
infection. The work provides precious information on the strategies
used by bacteria to manipulate their host cells.



FULL STORY ========================================================================== Legionellosis or Legionnaires' disease affected more than 1,800 people
in France in 2019 and caused 160 deaths. This emerging disease is caused
by Legionella pneumophila, an environmental bacterium that thrives in
hot water systems. Researchers from the Institut Pasteur, the CNRS, the University of Paris have discovered a mechanism that allows Legionella pneumophilato target the immune response of the cells it infects by
secreting a small regulatory RNA. This mechanism, not described before, facilitates the survival and proliferation of Legionella pneumophila
during infection. The work provides precious information on the strategies
used by bacteria to manipulate their host cells. This research has been published online on February 9 on the Nature Communications website.


========================================================================== Intracellular pathogens adopt various strategies to circumvent immune
defenses and proliferate inside the cells they infect. Legionella
pneumophila has a large repository of effector proteins* that mimic host
cell functions and are used by the pathogen to manipulate host signaling pathways to the pathogens advantage.

The teams of Carmen Buchrieser, head of the unit Biology of the
Intracellular Bacteria at the Institut Pasteur and associated to CNRS,
in collaboration with Gregory Lavieu at the Universite' de Paris and
associated to Inserm and CNRS, have discovered that Legionella pneumophila secretes extracellular vesicles into the host cell during infection in
which it packs small, regulatory RNA molecules. These regulatory RNAs
mimic eukaryotic regulatory RNAs called micro RNAs that already exist
naturally in the host cell.

The researchers have discovered that these two bacterial RNAs, named RsmY
and tRNA-Phe, function in the host cell in a microRNA-like manner. They downregulate RIG-I, a protein in the cell that detects foreign RNA
molecules in order to initiate an immune response. The down regulation
of the expression of RIG-I leads to a diminished host immune response
and a better replication of Legionella pneumophila.

This work sheds new light on the diverse, sophisticated strategies
employed by intracellular pathogens for survival and development during infection.

* Proteins secreted in the host cell via a
dedicated secretion system called type IV secretion system ========================================================================== Story Source: Materials provided by Institut_Pasteur. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Tobias Sahr, Pedro Escoll, Christophe Rusniok, Sheryl Bui,
Ge'rard Pehau-
Arnaudet, Gregory Lavieu, Carmen Buchrieser. Translocated Legionella
pneumophila small RNAs mimic eukaryotic microRNAs targeting the
host immune response. Nature Communications, 2022; 13 (1) DOI:
10.1038/s41467- 022-28454-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220218100648.htm

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