By Will Dunham

WASHINGTON, Feb 13 (Reuters) - Scientists have discovered a promising new method to fight a range of diseases by boosting the body's natural defenses against viruses.

Mauro Costa-Mattioli of McGill University in Montreal, who helped lead the research published on Wednesday in the journal Nature, expressed hope that the results achieved in mice might lead to new antiviral drugs for people.

The researchers inactivated two genes in mice that repress production of interferon, a protein that serves as a cell's first line of defense against viruses. The mice produced much higher levels of interferon, which had the effect of preventing the viruses from reproducing.

The technique made the mice and their cells resistant to infection by the influenza virus and a handful of other viruses, Costa-Mattioli's team said. The mice did not appear to experience any negative consequences from the augmented interferon production.

The process of inactivating genes -- known as "knocking out" genes -- cannot currently be done in people, but the scientists said they hope that drugs can be designed to affect the two genes in order to protect people from viral infection.

"Hopefully we will mimic the results we got genetically with pharmacology," Costa-Mattioli said in a telephone interview. "I think it's going to be an important step forward."

Viral infections are among the most common diseases, ranging from influenza to AIDS, and can be very difficult to fight.

Viruses enter living cells and exploit their reproductive machinery to sustain and replicate themselves. Interferon suppresses this viral propagation.

"People have been worried for years about potential new viral pandemics, such as avian influenzas," Nahum Sonenberg, a Howard Hughes Medical Institute international scholar at McGill who worked on the study, said in a statement. "If we might now have the means to develop a new therapy to fight flu, the potential is huge."

The researchers said the method holds the potential to combat a range of viral diseases.

"We hope that we will also be able to stop other viruses like Ebola and others, based on what we have so far," Costa-Mattioli said. "I think it's going to block a few of them or a majority of them, but I cannot promise. I would be very naive to say we've saved the world." (Editing by Maggie Fox)

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