麻豆传媒

INFECTION with a rotavirus, the commonest cause of gastro-enteritis in
children, may lead to childhood diabetes. Although this suggests that rotavirus
vaccines could help prevent diabetes, it also raises fears that the vaccines
themselves could trigger the disease.

Australian researchers discovered the link after a six-year study of 54
babies. 鈥淚t鈥檚 the most important piece of work I鈥檝e heard of in a long time,鈥�
says diabetes researcher Glenys Thomson at the University of Berkeley in
California. 鈥淭he evidence so far is looking very good.鈥�

Unlike type II diabetes
(see p 10), which usually affects people in middle
age, type I diabetes is an autoimmune disease that tends to start early in life,
and genetic susceptibility is an important factor. The disease develops when the
immune system attacks cells in the pancreas that produce insulin, which means
that the body can鈥檛 control its blood sugar levels properly.

Two years ago, Margo Honeyman of the Walter and Eliza Hall Institute of
Medical Research in Melbourne reported a possible link between diabetes and
rotaviruses. She had noticed that parts of some rotavirus proteins are similar
to parts of proteins on the pancreatic cells that trigger the destructive immune
response (Nature Biotechnology, vol 16, p 966).

To investigate further, Honeyman鈥檚 team monitored the progress of 54 babies
for up to six years. All had a parent or sibling with type I diabetes and so
were at risk of developing the disease.

As expected, all the children became infected with rotaviruses during the
study. In the 24 children who showed clear signs that they were developing
diabetes, levels of antibodies in their blood that signal an attack on the
pancreas went up almost every time they got a rotavirus infection. The
antibodies then dropped until the next infection. Children who didn鈥檛 develop
diabetes showed no signs of their pancreas being attacked following a rotavirus
infection. Neither did the rotavirus trigger an increase in antibodies against
any other organs.

How the virus might trigger diabetes isn鈥檛 yet clear. It may damage cells in
the pancreas directly when it infects them. Alternatively, it might mimic the
pancreatic proteins that incite the immune system to attack.

If mimicry is the answer, it could spell trouble for some of the rotavirus
vaccines being developed. The hope is that these vaccines will save the lives of
thousands of children in poor countries who die from gastro-enteritis each year.
But the tamed virus in some vaccines might also trigger diabetes in susceptible
children.

鈥淚f rotavirus is directly infecting the pancreas then a vaccine will be safe
and protective,鈥� says Honeyman. 鈥淏ut if it鈥檚 mimicry alone, or both infection
and mimicry, the vaccines may be dangerous.鈥�

鈥淚t鈥檚 fairly convincing evidence that rotavirus might be one of the triggers
for juvenile onset diabetes,鈥� comments virologist David Cubitt of the Great
Ormond Street Hospital in London. 鈥淭he idea of molecular mimicry is extremely
interesting, but obviously lots of other bits of the puzzle need to be put
颈苍.鈥�

Honeyman鈥檚 team is hoping to fill in some of the gaps. By trying to infect
mouse pancreatic cells in culture, they hope to confirm whether, and how,
rotavirus damages the pancreas. Honeyman has not excluded the possibility that
other viruses are involved. Coxsackie B, for example, is a prime suspect.