Research at the Malaghan Institute of Medical Research has highlighted a process by which children might become allergic to peanuts, without ever tasting them.
Prof Graham Le Gros, Director of the Malaghan Institute, leads a team of researchers looking at the early immune responses that take place during the development of food allergy, of which peanut allergy is the most dangerous and long-lasting.
"A child doesn't just suddenly become allergic to peanuts," says Prof Le Gros. "Their immune system has to have seen the peanuts beforehand, and become sensitised to them. It is the resulting runaway immune response that is responsible for the symptoms of food allergy such as swelling, skin irritations and breathing difficulties."
"Parents of allergic children will often say however that their child has never eaten peanuts, so we wanted to know how and why these children go on to develop peanut allergies."
To answer this question Prof Le Gros and senior allergy researcher Dr Elizabeth Forbes-Blom developed unique laboratory food allergy models to investigate whether other routes in the body, such as skin contact, were relevant for sensitising the immune system to peanuts.
These investigations were conducted using mice with fluorescent (glow in the dark) tags - when the mice experience an allergic reaction the affected cells glow, allowing researchers to see why they react. Their findings have just been published in the international journal of Clinical & Experimental Allergy.
"We know that children with recognised peanut allergies can have severe allergic reactions to skin creams or oils containing peanut extracts, without having to actually eat the products," says Prof Le Gros. "This is why early childhood centres in New Zealand are zoned completely peanut free."
"Recent clinical and experimental investigations also suggest an intriguing correlation between the development of peanut allergy, food exposure through the skin and the presence of eczema in early childhood," he says.
The skin of most patients with eczema is colonised with Staphylococcus aureus, and particular toxins produced by these bacteria can make their allergic skin irritations significantly worse. These same infections are also being increasingly implicated in the development of food allergies.
"We sought to bring all this information together and use our models to ask the question - what happens at the cellular level when the skin of an individual with eczema (and most likely a Staph infection) comes into contact with peanut extract? Are they more likely to go on to develop a peanut allergy?"
In short, their answer was "yes".
Prof Le Gros' team showed that specific bacterial products known as superantigens can amplify the immune response that develops in response to peanut extract coming into contact with the skin. On subsequent skin exposure, the allergic immune response to peanuts was even stronger, even in the absence of the bacterial toxins.
"Previous clinical data suggest that repeated exposure of the skin to peanuts can lead to the development of peanut specific allergic immune responses," says Prof Le Gros. "Our data show how this could be happening at the cellular level and highlight the importance of concomitant Staph infections in amplifying this process in individuals with eczema."
"Collectively these studies support the view that under some circumstances, having a child's skin come into contact with certain foods such as peanuts is all that is required for them to develop an allergic immune response - something that needs to be taken into consideration when developing treatments for food allergy sufferers."
This research was funded by the Health Research Council of New Zealand, the Foundation for Research, Science and Technology, Lotteries Health Research, The Dr Marjorie Barclay Trust and the Wellington Medical Research Foundation.
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