Neurolisteriosis: How Listeria Crosses the Blood–Brain Barrier Finally Explained

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

Listeria Monocytogenes

Listeriosis is a rare but potentially fatal foodborne infection. Although there are only about 1,600 cases a year in the US, about 260 infected patients die from it according to the CDC. It is particularly serious in pregnant women, newborns, and people with weakened immune systems. Listeriosis is caused by the bacterium Listeria monocytogenes. Some strains of this bacteria can reach the central nervous system and cause one of the most feared complications of listeriosis: neurolisteriosis.

The central nervous system, consisting of the brain and spinal cord, is particularly well protected and isolated from the rest of the body thanks to the blood-brain barrier. But how does the bacterium manage to infect the brain? This is the question that a team of researchers has managed to answer. Their work was published on March 16, 2022, in the journal Nature.

A cocoon of protection

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

Listeria appears to pass through the brain via a particular type of white blood cell, the inflammatory monocytes. The infected monocytes become protective cocoons for the bacteria and spread the infection throughout the body via the bloodstream. Infected monocytes should be destroyed by T cells long before they reach the brain. It seems that this is not the case thanks to a surface protein present in listeria, InlB.

This protein has the ability to protect the bacteria from the immune system and, in particular, from the cytotoxic action of T lymphocytes. It thus promotes the spread of the infection in the body – the brain – but also in the other organs. In addition, it allows bacteria to remain in the intestine. Thus, the bacteria appear in large quantities in the stool (and later in the environment) and can infect other people.

Final thoughts

In short, the bacteria cause the infected cells to extend their life span. This is a totally unexpected and very original mechanism! A better understanding of this process could lead to the development of new treatments that could stop the spread of bacteria in the body. It is also possible that similar strategies could be used by other pathogens capable of reaching the brain, such as toxoplasmosis or tuberculosis.