A previously unknown natural defence against swine flu and other viruses has been discovered which could lead to new treatments.
The virus-fighting proteins were identified 25 years ago but their role has been a mystery until now.
Scientists found that knocking them out of human cells allowed the H1N1 swine flu virus to run wild, but when their levels were artificially increased, replication of the viruses was completely blocked.
The discovery came by accident as researchers investigated viral infection in laboratory-grown cell cultures.
Screening the cells for molecules that assisted infection, the scientists stumbled upon one that shut viruses out.
The protein, IFITM3, belongs to a family of three molecules first described in 1984. Although they appeared to be linked to the immune system, their function had never been understood.
Genetically disrupting production of IFITM3 led to the swine flu virus replicating five to 10 times faster.
The same effect was seen in a range of cell types, including human and mouse lung cells, and with different H1N1 strains.
Then, instead of knocking out IFITM3 production in cells, the scientists boosted it, and stopped the virus in its tracks.
The protein’s cousins, IFITM1 and IFITM2, were found to have the same properties, although less powerful.
To the scientists’ surprise, raised levels of the proteins also blocked the replication of completely different viruses. They included West Nile virus and dengue virus, both of which cause serious human diseases.
Professor Stephen Elledge, from Harvard Medical School in Boston, US, who led the research, said: “We’ve uncovered the first-line defence in how our bodies fight the flu virus.”
Copyright Press Association 2009