London, Sep 30 (IANS): In a discovery that may lead to treatments that can slow or reverse cognitive decline in the elderly, researchers have found evidence of a unique "signature" in the ageing brain.

The immune system plays an important role, both in healing the brain after injury and in maintaining the brain's normal functioning, the findings showed.

This "signature of ageing" exists solely in the choroid plexus, the interface where brain-immune interaction occurs.

"The choroid plexus acts as a 'remote control' for the immune system to affect brain activity," said Michal Schwartz, a professor at Weizmann Institute of Science in Israel.

They discovered that one of the main elements of this signature was interferon beta - a protein that the body normally produces to fight viral infection.

This protein appears to have a negative effect on the brain: When the researchers injected an antibody that blocks interferon beta activity into the cerebrospinal fluid of old mice, their cognitive abilities were restored, as was their ability to form new brain cells.

The scientists were also able to identify this unique signature in elderly human brains.

This finding led the researchers to suggest that cognitive decline over the years may be connected not only to one's "chronological age" but also to one's "immunological age".

That means change in immune function over time might contribute to changes in brain function - not necessarily in step with the count of one's age.

The scientists hope that this finding may, in the future, help prevent or reverse cognitive decline in old age, by finding ways to rejuvenate the "immunological age" of the brain.

The study was published in the journal Science.