Cold viruses activate killer genes, study finds

WASHINGTON (Reuters) - The common cold virus activates dozens of immune system genes in the lining of the nose, including some natural antivirals that might be used as the basis of new drugs, researchers reported on Friday.

It also appears to shut down some genes, but to a lesser degree, the international team reported in the American Journal of Respiratory and Critical Care Medicine.

Of particular interest is a gene that controls a natural antiviral called viperin, said David Proud of the University of Calgary in Alberta, who led the study.

Viperin, only discovered in the 1990s, was known to be involved in other viral infections but not the common cold, Proud said. "This had never been examined during rhinovirus infections," he said.

Proud and colleagues, including a team at cold remedy maker Procter & Gamble Co, tested 35 people who agreed to be infected with a common cold virus called human rhinovirus 16.

Hours after infection, the researchers scraped a little bit of the lining from inside the volunteers' noses and analyzed gene expression, or activity, in the cells.

Every cell in the body carries all the genes, but certain genes become more or less active during various activities.

"I think that is the ideal approach to trying to treat these viral infections. If you can find out what are the body's natural defenses, can you either boost them or supplement them?" Proud said in a telephone interview.

"The findings are important because they provide us a blueprint for developing the ideal cold treatment: one that maintains the body's natural antiviral response while normalizing the inflammatory response," added P&G's Lynn Jump, who also worked on the study.

Others had looked at immune responses one by one. "This was really the first study that looked at the entire human genome," Proud said. "We confirmed some of the things we knew, and we found an awful lot more that we weren't aware of."

For instance, you might be able to blame a runny nose, sneezing and chills on viperin, the researchers found. Symptoms such as a stuffy nose, headache and cough were not associated with viperin, however.

Several immune system chemicals called chemokines, which call in other virus-killing cells, became very active 48 hours after infection, they found. So did a class of immune system compounds called interferons.

Viperin, on average, was six times as active in infected as in uninfected volunteers. Other antiviral substances that were activated included compounds called MX1 and MX2, which are linked with resistance to influenza.

Proud said it will take years of careful study before researchers have any idea of how to control cold symptoms. "You need a little bit of inflammation to have some protection," he noted.

More than 200 different viruses cause common cold symptoms, including the rhinoviruses but also others such as respiratory syncytial virus or RSV.

Many, including RSV and rhinoviruses, are linked with more serious conditions such as asthma and chronic bronchitis, now grouped with emphysema as chronic obstructive pulmonary disease.

"In young children, if they have recurrent viral infections in early life that are rhinovirus-driven, they are 10 times more likely to develop asthma," Proud said.

"Eighty-five percent of acute asthma attacks are associated with viruses."

(Editing by Julie Steenhuysen and Eric Walsh)