How does listeria infect the brain?

Listeriosis is a rare but serious disease. When it reaches the central nervous system, it can be fatal. But how does it manage to cross the blood-brain barrier that isolates the brain from the rest of the body?

The listeriosis is a rare but potentially fatal foodborne infection. If it represents only a hundred cases per year in France, around 25% of infected patients will die. It is particularly serious in pregnant women, newborns and immunocompromised people. Listeriosis is caused by listeria bacteria. Some strains of this bacterium have the ability to achieve central nervous system and cause one of the most feared complications of listeriosis: neurolisteriosis.

The central nervous system, made up of the brain and spinal cord, is particularly well protected and isolated from the rest of the body, in particular thanks to the blood-brain barrier. But then, how does the bacterium manage to infect the brain? It is to this question that a team of researchers has managed to provide an answer. Their work has been published in the prestigious journal Nature on March 16, 2022.

A protective cocoon

To study the passage of the bacterium in the central nervous system, the authors used a mouse model reflecting neurolisteriosis. They took virulent strains of listeria from patients with neurolisteriosis.

Listeria appears to enter the brain via a certain type of white blood cell, monocytes inflammatory. Infected monocytes turn into protective cocoons of the bacteria and spread the infection throughout the body through the bloodstream.

A surface protein involved

Infected monocytes should be destroyed by T cells well before reaching the brain. It seems that this is not the case thanks to a protein surface present in listeria, InlB.

This would have the ability to protect the bacteria from immune system and in particular the effect cytotoxic T cells. Thus, it promotes the spread of infection in the body – the brain – but also other organs. In addition, it allows the persistence of the bacteria in the intestine. It is therefore found in excrement (and then in the environment) in large quantities and can contaminate other people.

In conclusion, the bacterium allows infected cells to prolong their duration of life. This is a totally unexpected and very original mechanism! A better understanding of this process could lead to the development of new treatments capable of blocking the spread of the bacteria in the body. Moreover, it is possible that similar strategies are used by other pathogens capable of reaching the brain, such as those of the toxoplasmosis or the tuberculosis.