Researchers in Switzerland have developed a detector for anthrax spores based on a monoclonal antibody that recognizes a specific sugar on the bacterium. Once inhaled, spores of Bacillus anthracis almost always kill, unless victims are treated within a day or two. According to Peter Seeberger of the Swiss Federal Institute of Technology (ETH) in Zurich and colleagues there and at the Swiss Tropical Institute, and the University of Bern, also in Switzerland, accurate and rapid diagnosis is essential if lives are to be saved.

The researchers have now developed a novel approach to anthrax detection based on immunology. This new test promises to be just as accurate but far simpler to carry out than current detection methods. Their detector is based on detecting anthrose, a sugar unique to anthrax spore surface carbohydrates. Antibodies raised against anthrose respond only to anthrax spores and not to bacteria closely related to B. anthracis. "Our results demonstrate that small differences in the carbohydrates on cell surfaces can be used to obtain specific immune reagents," says Seeberger, "Our new antibodies will be used as the basis for highly sensitive anthrax diagnosis and will contribute to the development of new therapeutic approaches."

Spores of the dreaded Bacillus anthracis have already been used as a bioweapon against civilians. Once inhaled, the anthrax pathogen almost always leads to death if the victims are not treated within 24 to 48 hours. There are several diagnostic tests for anthrax but they are time-consuming. In the event of a bioweapon attack, a quicker and simpler test could save many lives. Diagnostic tests based on immunology are usually very simple and quick. However, the surface features of anthrax spores are very similar to other common bacteria so early immunological tests for anthrax fail to distinguish between these and deadly anthrax.

Fortunately, scientists discovered a carbohydrate consisting of four sugar components on the surface of anthrax spores. Three of these sugar molecules are found in other bacteria, but the fourth turned out to be unique to anthrax and has been named anthrose. Seeberger and his team focused on this sugar molecule as the flag they needed to diagnose anthrax.

To make a fast immunological test for any disease, scientists have to make special proteins known as antibodies, which detect and latch on to the target molecule. Seeberger and his team synthesized anthrose in the laboratory and then attached this sugar to a "carrier" protein. This innocuous sugar-protein complex was then injected into mice. The mouse immune systems quickly spots the invading molecule and recognizes it as alien, triggering the production of antibodies. These antibodies are specific to the sugar molecule. The researchers could then mass produce these antibodies in the laboratory to incorporate into their test kit.

When they tested the antibodies against anthrax, they found that they bind very specifically only to anthrax spores and no other closely related bacteria. "Our results demonstrate that small differences in the carbohydrates on cell surfaces can be used to obtain specific immune reagents," explains Seeberger, "Our new antibodies will be used as the basis for highly sensitive anthrax diagnosis and will contribute to the development of new therapeutic approaches."

It might be possible to use this discovery to develop a passive immunization method. "First of all, however, we want to test an active vaccination for humans," says Seeberger. In fact, with his synthetically produced anthrose bonded to the transport protein, he has already created the basis for a vaccine.

Angew Chem, 2006, in press; http://dx.doi.org/10.1002/anie.200602048

http://www.seeberger.ethz.ch/people/seeberger