November 14, 2013
Scientists Solve Half-Century Old Anthrax Mystery
Brett Smith for redOrbit.com - Your Universe Online
For years, doctors have wondered why someone with an anthrax infection can die days after the bacteria responsible is wiped out from their body. A new study claims the toxin produced by the bacteria uses a “Trojan horse”-like method to elude the body’s natural defenses.
"This remained a mystery for more than 50 years,” said study author Gisou van der Goot, a cell biologist at Switzerland's prestigious École Polytechnique Fédérale de Lausanne (EPFL). “The bacteria would disappear after the administration of antibiotics, but the subject still died a few days later.
"The anthrax bacteria kills people in a very short period of time, and this is in large part due to the production of the anthrax lethal toxin," she explained. "This toxin disarms our immune system, but also, as very recently shown, affects our heart."
Believing the anthrax toxin was behind these somewhat mysterious deaths, the international team focused on how the toxin entered the body's cells. They found the relevant part of the cell's defenses is made up of two components – a protective antigen and a lethal factor. This protective antigen ferries the lethal factor into cells by helping it to cross the cell membrane, according to the team’s report in the journal Cell Reports.
Once the toxin is inside the cell, the lethal factor is actually engulfed by the cell's membrane, forming a sheltering ‘endosome.’ After waiting in the endosome for up to for several days, it can either be released into the cell, disrupting it, or out of the cell, allowing it to enter another cell. The research team also found that the toxin can also be passed on from a cell to its progeny.
"The immune system has no reason to react, since it only detects exosomes whose membrane is composed by the very same molecules making up the cell's endosomes." van der Goot explained.
The study team said their findings help to explain not only why an anthrax infection is so deadly, but also how cell membranes interact with various substances.
"By studying these interactions, we can learn more than how to fight anthrax infection," van der Goot said. "We also learn a lot about how cells work.
“There is still much to learn about exosomes,” she added. “The results of this research will help us to better understand them.”
The team said their study could lead to the development of drugs that target the lethal factor while contained within the cell's membrane.
Named after the Greek word for 'coal,’ anthrax can form black lesions on the skin of people it infects. The Ames strain of the bacterium became well-publicized in 2001 after it was linked to several infections in the United States.
The more dangerous Vollum strain of the bacterium was weaponized during the Second World War, but never used. Isolated in 1935 from a British bovine, the Vollum strain was tested by British military scientists on the Scottish island of Gruinard.
For the weapons test, 80 sheep were taken to the island where bombs containing the deadly strain were detonated. The sheep died within days of exposure. Military films depicting the tests were declassified in 1997.