Scientists crack secrets of TB bug
Scientists have cracked the secret of how the tuberculosis bug survives and spreads inside the lungs.
They hope the discovery will lead to new ways of fighting TB, which causes more deaths worldwide than any other potentially curable infection.
Mycobacterium tuberculosis invades immune system cells in the lungs and keeps them alive to function as temporary incubators.
The bacteria multiply within the macrophage white blood cells and then burst out to infect other cells.
Normally a biological “fail-safe” mechanism would destroy the infected cells, wiping out the invading bacteria at the same time and triggering an immune response.
But M. tuberculosis prevents this kind of planned “cell suicide”, called apoptosis, from taking place, scientists have learned.
Instead the cells die an unnatural form of death called necrosis, which allows the replicated infectious bacteria to escape and evade the immune system.
Experts hope the research, published in the journal Nature Immunology, will help them develop new drugs to stop the TB bug spreading.
The US study led by Dr Heinz Remold, from Harvard Medical School in Boston, showed that the bacteria blocked a key mechanism essential for cell suicide.
A cell earmarked for death by apoptosis should develop an impermeable membrane barrier on its outer surface called the “apoptotic envelope”.
The envelope prevents potentially harmful elements such as infectious bacteria escaping from the cell. It also sends out signals to attract phagocytes, amoeba-like immune system agents that engulf and dispose of infected or damaged cells.
But the apoptotic envelope is missing from cells attacked by M. tuberculosis.
The researchers wrote: “Virulent M. tuberculosis ... avoids the host defence system by blocking formation of the apoptotic envelope, which leads to macrophage necrosis and dissemination of infection in the lung.”
Around nine million new cases of TB and almost two million deaths are reported around the world each year.
TB is caught by inhaling tiny droplets produced by sneezing and coughing.
