Bacterial hideout could be source of TB reactivation

22 February 2016

Bacteria that cause tuberculosis can live in the walls of lymph vessels. The discovery, made by scientists at the Francis Crick Institute, 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. 

TB bugs attached to lymph cells. This electron micrograph image shows the long, thin bacteria.

TB bugs attached to lymph cells. This electron micrograph image shows the long, thin bacteria.

 

  

 

  

These TB bacteria can live inside lymph node cells.

These TB bacteria can live inside lymph node cells.

 

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 Gutierrez 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."

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

  • Tuberculosis-causing bacteria can live in the walls of lymph vessels, according to new research by Francis Crick Institute scientists.
  • The research may explain why people can be treated for extrapulmonary TB and recover, but then get the infection again.