Go nuts for new allergy clue

6 July 2007

Experts have uncovered a vital clue that helps explain why peanuts can send some people's immune systems into overdrive. They've found that peanut-allergic mice are missing a key immune molecule, a discovery that could bring new treatments for the killer allergy. Antenna investigates...

Around 1 in 70 children are thought to be allergic to peanuts.

Image: iStockphoto.com/Mark Dietrich

A peanut allergy, like all allergies, involves two steps. First, your immune system has to become sensitive to peanuts. This can happen at any time. For some reason, the immune cells in your gut can react to a peanut as if it's something bad. They produce special Y-shaped molecules called antibodies, which spread throughout your body.

The second step occurs the next time you eat a peanut - the antibodies lock onto it, triggering a powerful reaction from your immune system. In severe cases, this can cause 'anaphylactic shock', which can be fatal if you don't get a shot of adrenaline in time.

Antibodies are produced by 'B' cells, shown above.

Image: Michelle Peckham, University of Leeds/Centre for Bioscience ImageBank

A tough nut to crack...

'We need to understand why the immune system goes ballistic,' says Claudio Nicoletti, from the Institute of Food Research in Norwich. 'But it's too dangerous to do this research in humans, and too complicated for a test tube. Instead we use mice, whose immune system matches ours very closely.'

Claudio Nicoletti, Institute of Food Research.

Image: Institute of Food Research

Although mice have a very similar immune system to our own, they are normally pretty resistant to allergies. Scientists only worked out how to mimic human food allergy in mice in 2000.

Claudio and his team studied mice that were prone to develop allergic reactions to food. They focused on a certain type of immune cell in the mice's gut called a 'dendritic' cell. 'Dendritic cells act like an orchestral conductor,' explains Claudio. 'They tell the other immune cells what to do.'

'We found that the dendritic cells in the gut of mice with a peanut allergy don't produce an important immune molecule called IL-12,' says Jeff Temblay from the Institute of Food Research.

Jeff Temblay, Institute of Food Research.

Image: Jeff Temblay

The large cell in the top left of this image is a dendritic cell, shown interacting with other cells of the immune system.

Image: Claudio Nicoletti

In mice with a peanut allergy, IL-12 is missing at a crucial time in the immune reaction - the point at which the dendritic cells tell the other immune cells how they should react to peanuts. Without IL-12, the other immune cells respond as if peanuts are harmful.

'We now have a target for a potential treatment for food allergy,' says Claudio. 'We're working with another team of scientists to genetically engineer "friendly" bacteria that can release IL-12 into the gut.

'Further research will tell us whether giving peanuts together with IL-12 to a person with an allergy might re-establish a normal immune response to peanuts, potentially curing their allergy.'

The lining of the gut is covered with 'Peyer's patches', which have a high concentration of immune cells. Delivering IL-12 to these areas might help people with food allergies.

Image: Gordon Beakes, University of Newcastle upon Tyne/Centre for Bioscience ImageBank

Allergy charities think Claudio's findings are good news. 'Food allergy can place an extremely heavy burden on the families affected,' says David Reading from the Anaphylaxis Campaign. 'We welcome this research and look forward to further developments.'

'This research offers hope to the increasing number of people affected by food allergy,' adds Muriel Simmons from Allergy UK.