Food allergy mechanism comes to light

07-May-2004

Related topics:Public Concerns

New research from the UK suggests an immune system malfunction couldplay a profound role in the onset of food allergies. As the Europeanfood industry gets to grips with imminent rules on the labelling ofallergens, the UK findings will help industry and consumer alike.

Escalating incidences of food allergies in Europe and the desire toavoid potentially harmful consumer confusion underpinned changes to theLabelling Directive 2000/13/EC due to enter into force in November 2004.The changes herald the mandatory inclusion on food labels of the mostcommon food allergen ingredients and their derivatives: cerealscontaining gluten, fish, crustaceans, egg, peanut, soy, milk and dairyproducts including lactose, nuts, celery, mustard, sesame seed, andsulphites.

According to the European Federation of Allergy and Airways DiseasesPatients' Associations, estimated 4 per cent of adults and 8 per cent ofchildren in the European Union - the total population equals over 380million - suffer from food allergies.

While the cause of food allergies has remained a challenge for science, a team of scientists, led by the Institute of Food Research (IFR)in the UK, found that two types of cells stop communicating. This meansthat the programmed cell death of one type of cell fails to happen.Programmed cell death is one of the most important mechanisms formaintaining health in mammals.

"There are two stages to food allergy", said research leader DrClaudio Nicoletti at the IFR. The first is sensitisation, when theimmune system starts producing an antibody in response to eating a food.The second is when that food is eaten for a second time, triggering anallergic reaction.

"We have identified an immune response malfunction that occurs in thesensitisation stage, which could provide a target for futuretherapies," he said.

There is no current cure for food allergy and vigilance by an allergicindividual is the only way to prevent a reaction. In allergic reactionsthe body overproduces the antibody IgE causing many symptoms includingskin rashes, wheezing, sneezing, swelling around the lips, bloating,vomiting and diarrhoea. In extreme cases it causes anaphylaxis, alife-threatening reaction triggered within minutes.

Two critical cells types for regulating immune response are dendriticcells and T-cells. Dendritic cells are white blood cells with finebranches called dendrites. They are stationed at parts of the body mostlikely to come into contact with pathogens, particularly the skin andmucous membranes. They capture a section of any foreign body, deliver itto other immune cells such as T-cells and instruct these cells to dealwith the intruder.

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A class of T-cells called T helper 2 cells (Th2) was thought to play animportant role in sensitisation to harmless substances including food.But research by IFR scientists questioned this assumption, so theyshifted focus for the current study.

No one had looked at the communication between dentritic cells andT-cells in food allergy. Once dendritic cells have given theirinstruction, they normally die. The scientists found that in allergy,dendritic cells escape death. This could mean that they keep onactivating T-cells to create antibodies.

"Dendritic cells are one of the most fascinating cell types in the immune system," said Dr Nicoletti. "Itappears that in allergy they get out of control, and this malfunctioncould have a profound effect on the development of food allergies."

Welcomed by allergy associations, last November Europe confronted thefood industry with new rules - to enter into force in November 2004 - onfood allergen ingredients when Brussels cleared Directive 2003/89/EC,amending Directive 2000/13. Food manufacturers will have to list allsub-ingredients of compound ingredients, which means that allergenscannot be 'hidden', heralding an end to the 20 year old 25 per cent rulewith all ingredients labelled, regardless of the quantity contained inthe finished food.

Europe's risk assessment body, the European Food Safety Authority (EFSA)recently concluded that current scientific evidence is 'insufficient toestablish an intake threshold' for food allergens.

Cereals, peanuts, soy and dairy products were among a range of potentialallergens investigated by the Dietetic Products, Nutrition andAllergies (NDA) panel, part of EFSA, at the request of the Commission.Their findings show 'ample evidence' to justify a list of allergenicingredients and their derivatives on the food label.

"In no case is the available evidence sufficient to establish anintake threshold below which allergic reactions are not triggered, or topredict reliably the effect of food processing on allergenicpotential," said Professor Albert Flynn, chair of EFSA's NDA panel.

Full findings of the IFR led study conducted with the University of Sienna, Italy are published in the Journal of Allergy and Clinical Immunology (Vol. 113, No. 5, May 2004, pp965-972).