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Last Updated: Thursday, 17 July, 2003, 10:15 GMT 11:15 UK
How anthrax evades attack
Bacillus anthracis - Image by WHO/P.Virot
Anthrax is a deadly infection
Scientists have discovered how anthrax avoids attack by the immune system.

They hope the finding could lead to more effective treatments for the deadly infection - and for auto-immune diseases such as multiple sclerosis.

The researchers have found out that the key is one of three poisonous proteins produced by anthrax - called lethal factor.

Our ultimate goal is to apply this novel finding to develop better anthrax treatments
Dr Bali Pulendran
This chemical is able to disable dendritic cells, which in normal circumstances are mobilised by the immune system to attack an invader.

Researcher Dr Bali Pulendran, of Emory University in Atlanta, Georgia, said: "This is the first study that demonstrates any interaction between bacillus anthracis (anthrax) and dendritic cells.

"When dendritic cells are compromised, such as in our study, the innate immune system is unable to stimulate the immune response, thus permitting the microbe to spread unchecked."

Combination of poisons

Lethal factor and two other toxins, protective antigen and edema factor, increase the deadly potency of anthrax.

The edema factor causes the release of fluid into the lungs and is deadly on its own.

Protective antigen shields the other two toxins from the immune system, allowing them to enter target cells, and lethal factor destroys immune system cells.

When they die, they trigger a reaction in the body that can cause septic shock and death.

Dr Pulendran said: "Our ultimate goal is to apply this novel finding to develop better anthrax treatments and to shape future research into controlling immune responses more appropriately."

The researchers hope that as lethal factor has the ability to disarm the immune system it could potentially form the basis of drug that are able to block inappropriate immune reactions in autoimmune diseases or in transplant patients.

The study is published in the science magazine Nature.

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