Bacterial hideout could be source of TB reactivation

immune, tuberculosis

Bacteria that cause tuberculosis can live in the walls of lymph vessels. The discovery, made by scientists at The Francis Crick Institute in London, could explain why people can be treated for TB hiding outside the lungs, recover and then get it again.

A team led by Dr. Max Gutierrez found Mycobacterium tuberculosis bacteria intact inside cells taken from samples of human lymph tissue.

The number of people affected by TB that takes hold outside of the lungs – extrapulmonary TB – has increased dramatically in the past decade. Lymph nodes are the most common site of infection. Almost one in five people who are HIV positive experience extrapulmonary TB.

This is the first time that endothelial cells, that line the walls of the lymph vessels, have been shown to have a role in TB.

The study was done using tissue samples from people living in South Africa whose lymph nodes were removed as treatment for extrapulmonary TB. However, the problem is known to exist worldwide.

The team infected endothelial cells taken from human lymph vessels with TB bacteria in the lab. They followed their progress using microscopic imaging to find out exactly where within the cell the bacteria multiply. Most of the bacteria were discovered in the fluid inside the lymph cells, but some were found growing in autophagosomes – a sort of cell bag that usually swallows and destroys bacteria.

Dr. Max Gutierrez led the research, he said: “Depending on how active the immune system is, the cells forming the walls of lymph vessels can actually provide a reservoir for TB bacteria that allows them to multiply as well as hide. If the cells are properly activated by the immune system the bacteria are destroyed, if not, they can grow.”

“This is the first time we have been able to show that TB bacteria can live in these cells in the lymph nodes and suggests they are a source of re-infection even after treatment,” Gutierrez concluded.

The research paper, Lymphatic endothelial cells are a replicative niche for Mycobacterium tuberculosis is published in the Journal of Clinical Investigation.

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The Francis Crick Institute is a new and distinctive biomedical research institute. Its purpose built laboratory in the King’s Cross area of London will open in 2016.  The institute’s work – which is already underway at the Crick’s Clare Hall, Lincoln’s Inn Fields and Mill Hill laboratories – will help to understand why disease develops.

We will find new ways to diagnose, prevent and treat a range of illnesses − such as cancer, heart disease and stroke, infections and neurodegenerative diseases. We will bring together outstanding scientists from all disciplines, carrying out research that will help improve the health and quality of people’s lives, and keeping the UK at the forefront of medical innovation. The Francis Crick Institute is a charity supported by the Medical Research Council, Cancer Research UK, the Wellcome Trust, UCL (University College London), Imperial College London and King’s College London.