Immune link: Dendritic cell (red) , T cell (blue) , and HIV (green)
HIV harnesses the body's own immune system to help it spread rapidly throughout the body, scientists have discovered.
The same mechanisms which allow the body to respond quickly to infection are inadvertently allowing the virus to become established.
HIV scientists know that the virus manages to kill off vital immune cells, but are not sure how it manages to invade them in the first place.
Researchers from the University of Illinois at Chicago have actually managed to film HIV as it enters immune cells.
They believe their pictures show how the natural efforts of our immune systems to eradicate HIV end up giving the virus a helping hand to get established.
There are many different kinds of cell which help generate a human immune response.
Dendritic cell (red) links with T cell (blue) - HIV (green) at the junction
One way the body protects itself against microbial attack starts when cells called "dendritic cells" encounter a foreign virus or bacterium.
They are supposed to pick up the microbe, break it up into tiny bits, then deliver these fragments to other cells called T cells.
These fragments alert the T cells to the presence of intruders, and other immune cells are mobilised to hunt them down.
HIV, says the research team, has found a way to subvert this process.
When it is picked up by dendritic cells, some copies of the virus survive intact.
The dendritic cells meet up with T cells, and open up a link called a "synapse", which allows material to pass from one to the other.
The Chicago time-lapse film shows the viruses seizing the opportunity offered by this "open door" to jump across into the T cell, where they can begin replicating, eventually destroying the cell.
It's a billion-year-old war - the body builds defences against viruses, and the viruses find ways to thwart those defences
Dr David McDonald, University of Illinois
Dr David McDonald, one of the researchers, said: "HIV exploits the dendritic machinery for its own ends, taking advantage of the cells' special relationship with T cells to gain entry and launch its assault.
"What viruses do is try to find weak points in the immune system and take advantage of them.
"It's a billion-year-old war - the body builds defences against viruses, and the viruses find ways to thwart those defences."
The scientists are hopeful that their finding could eventually produce strategies to protect T-cells from their unwelcome visitors.
And, they say, it is possible that other viruses may operate in a similar way.
The study was published in the journal Science.