Thousands of years of evolution have made the influenza virus a specialist in defeating our immune systems. A new discovery by Dalhousie University researchers finally shows how it accomplishes that.

By better understanding how the flu attacks, the scientists hope to come up with improved ways to treat it.

Normally when a virus infects a cell, that cell sets off an alarm to warn the immune system.

"The flu virus has a way of selectively blocking that alarm signal," says Craig McCormick, an associate professor in Dalhousie's department of microbiology and immunology.

Like all viruses, influenza invades a body's cells, injects its own genetic material into the cell, and then uses the cell to create copies of the virus.

The cell then splits open to release the new copies of the virus into the body. When it is infected, the cell will normally send out RNA molecules to alert the immune system.

But the Dalhousie researchers have discovered the flu virus cuts the RNA into pieces, disabling the alarm system as effectively as any burglar. That allows the virus to continue reproducing until the immune system eventually learns it is there.

We're co-evolving with 'viral babies'

It was previously thought that the virus might disrupt much of the cell's internal machinery to disable the immune response. However, the virus needs that machinery to reproduce, so it is very selective about what it disables.

"I think what's smart is the evolution," said Denys Khaperskyy, a research associate on the team.

"Viruses co-evolve with their hosts, so viruses can only survive if they can find a way to replicate in the host and produce viral progeny, viral babies."

The flu virus is inexact in the way it makes copies of itself, so in each infection there are a number of variations of the virus.

The ones that give it a genetic advantage survive. The ones that don't die off. That's how the flu developed its ability to disable the body's immune system and "cloak" itself.

It's also how the virus mutates so quickly and can return winter after winter to re-infect people who have already developed an immune response.

Natural killer cells

Natural killer — or NK — cells, are the body's first line of defence against viruses like influenza.

Another group of researchers led by Dalhousie's Andrew Makrigiannis found they could enhance the ability of NK cells to detect the virus.

The long-term goal is to use the two discoveries to come up with a new cure for the flu.

"We are very interested in unleashing the potential of the host cell and the immune system to basically control the virus, as opposed to conventional anti-viral drugs, which are targeting viral processes," said McCorrmick.

That would mean uncloaking the virus to give the immune system a chance to work, he said.