How tuberculosis bacteria survive has been identified by Indian researchers at the International Center for Genetic Engineering and Biotechnology in New Delhi.
Tuberculosis, caused by the bacteria Mycobacterium tuberculosis, is known to evade the immune system by hiding inside compartments called granulomas in infected lung and spleen tissues.
Despite immune responses by the body, the bacteria thrive inside the granulomas largely unharmed, establishing persistent infections that can prove lethal.
Now, the research team has found the bacteria recruit mesenchymal stem cells (MSCs) to sites of infection in the spleen and lungs. MSCs are normally found in the bone marrow, and typically diversify to form blood, bone, muscle and other tissues.
The researchers say the stem cells limit the spread of the granulomas, but don't completely eliminate them. They believe the tuberculosis bacteria is exploiting this mechanism to establish latent infections.
"I believe this is the first time that researchers have shown any infectious disease, TB or any other infectious organism, using the stem cells [of the host] for their survival," said Dr Gobardhan Das.
The stem cells form a protective coating around the granulomas and produce a range of immunosuppressant molecules, such as nitric oxide. This shields the tuberculosis bacteria from white blood cells and T cells, which would normally destroy the intruders.
"If you can target these MSCs then you can destroy the protective layer and expose the bacteria to the macrophages and T cells, and the immune system can then get in and attack the bacteria", Das said.
The research is published this week in Proceedings of the National Academy of Sciences.