curiosity. Now, for the first time, they have been linked to a disease that
Rather than the viruses causing infection directly, it is the proteins they make
that seem to be the culprit, triggering an immune response that led to arthritis
Meanwhile, blood tests from a small group of people with arthritis suggest
they are more likely than healthy people to carry antibodies to a particular
mimivirus protein that is of the type that comes under attack in the condition.
Though bigger studies in people are now needed, the findings suggest
mimiviruses could trigger some human cases of rheumatoid arthritis, which is
caused by the body's immune system attacking itself.
Discovered more than a decade ago in a cooling tower in Bradford, UK,
mimiviruses get their name because their size mimics that of bacteria rather
than other viruses. They are known to infect and kill amoebas, but no link to
disease in humans had previously been found.
While trawling through publically available gene libraries, Thierry Hennet of the
University of Zurich, Switzerland, noticed that mimiviruses make proteins
called collagens that are very similar to those made by humans.
Hennet's main research focus is how arthritis is affected by collagens. These
are the basic structural proteins in animals, which break down in rheumatoid
arthritis – and have never been seen in viruses before.
He wondered whether people coming into contact with mimiviruses, through
exposure to contaminated sea or lake water for example, might make
antibodies against the mimivirus collagen. These antibodies might then go on
to attack human collagen because it's so similar, eventually leading to
To investigate, his team injected mice with a mixture of 60 proteins that had
been extracted from mimiviruses bred in the lab, including several collagens.
They also injected a second group of mice with just one of these collagens,
L71, and a third group with just cow collagen, already known to trigger arthritis
The group that received the cow collagen developed the most severe…