Listeria, the bacterium that causes a rare but very dangerous food infection, sometimes manages to reach the brain by making certain infected cells resistant to the immune system, suggests a study published on Wednesday.
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This mechanism “allows these cells to survive longer in the blood and to pass in greater numbers into the brain”, summarizes this work, carried out on animals and published in the journal Nature.
Listeria is the cause of listeriosis. This food infection is rare – a few hundred cases per year in France – but, once declared, it is particularly deadly: around a quarter of patients die.
Among the complications that can cause these deaths is neurolisteriosis, that is to say a neurological attack caused by the passage of the bacterium in the central nervous system, which includes the brain and the spinal cord.
Carried out in several stages on laboratory mice, supposed to reflect the evolution of the disease in humans, the Nature study shows, initially, that listeria passes into the brain via certain white blood cells, monocytes .
The researchers then discovered how these infected cells reached the brain without being destroyed by the immune system. It is a protein found in listeria that seems to protect them.
This protein, called InlB, puts the affected cells under the radar of T lymphocytes, whose role is to destroy cells infected by a virus or a bacterium.
This mechanism “creates a cellular protective niche that encourages the dissemination and persistence of listeria” in the body, the study concludes.
Not only does it allow listeria to pass into the brain, but it also gives it time to survive in the gut and be present in feces. The bacterium can therefore be all the more present in the environment and continue to spread in this way.
This mode of action is a surprise, according to the researchers, who did not expect listeria to neutralize the action of T lymphocytes in this way.
It is a “specific and unexpected mechanism, by which a pathogen increases the lifespan of the cells it infects”, summarizes the researcher Marc Lecuit, who supervised this study, in a press release from the Institut Pasteur, to which are linked several authors.