How bacteria avoids human immune system: Revealed

Last Updated: Wednesday, March 31, 2010 - 12:14

Washington: In a key breakthrough,
scientists claim to have found how a major bacterial infection
avoids the human immune system -- ironically, a trick which
could help fight inflammation.

In its research, an international team, led by the
University of Auckland in New Zealand and Aarhus University in
Denmark, has revealed exactly how the superbug Staphylococcus
aureus evades human body`s key immune defences.

Lead scientist Prof John Fraser said the six-year-long
research focuses on a small protein from the superbug called
SSL7 (Staphylococcal Superantigen-like protein 7).

The scientists have shown how this protein binds to
Immunoglobulin A (IgA), a special defence antibody in our gut
and lung. The SSL7 protein also binds to complement C5, one of
a series of proteins that "complement" the work of antibodies
in destroying bacteria.

"We`ve created a structural model of the complex
formed when SSL7 binds to IgA and C5. The model has enabled us
to see how SSL7 cleverly uses IgA as a `scaffold` to capture
two molecules of C5.

"By doing this, the reaction that brings complement
proteins together to destroy the bacteria`s cell wall can`t
take place. By binding to IgA and C5 at the same time, the
SSL7 protein simultaneously blocks several crucial parts of
the body`s immune defence against bacterial infection," Prof
Fraser said.

According to the scientists, by knowing how S aureus
works to block immune system, researchers can begin to develop
therapeutic drugs that directly target proteins like SSL7.

"Remarkably, SSL7 highlights exactly where to pinpoint
drugs designed to prevent the unwanted over-activation of C5
that normally leads to a serious inflammatory disorder," Prof
Fraser said.

The findings have been published in the `Proceedings
of the National Academy of Sciences` journal.

PTI



First Published: Wednesday, March 31, 2010 - 12:14

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