Food Proteins: AllergensFood Proteins: Allergens

Hanne FrøkjærDepartment of Systems Biology

DTU

What is an allergen?What is an allergen?

’A substance which provokes an allergic reaction in individuals sensitive to thesubstance’

Hanne Frøkiær

WhatWhat is is AllergyAllergy??

’Hypersensitivity’

’Inappropriate immune responses against normally harmless antigens’

Hanne Frøkiær

What is an allergic reaction?What is an allergic reaction?

An inappropriate immunological An inappropriate immunological reaction against a usually harmless reaction against a usually harmless

substance.substance.-characterized by production of specific

antibodies (IgE), and release of histamine and other bioactive substances.

Hanne Frøkiær

Hanne Frøkiær

Food allergies and related symptoms

Most common food allergensHanne Frøkiær

•Milk•Eggs•Peanuts (and other legumes)•Tree nuts (cashew, walnut)•Shellfish•Fish•Grain (wheat, rice)

Allergens:Properties of most food allergens

� Heat stability

� Resistance towards acid

� Resistance towards proteolysis

� Glycoproteins

� Mw 10 kDa or more

Hanne Frøkiær

Allergy:Endogeneous factors affecting sensitation

� Genetic influence

� Underlying disease

� Diet

� Commensal flora

� Age

� Gender

Hanne Frøkiær

Hanne Frøkiær

Initiation of an allergic reaction

Second and later encounter with the allergen

Mast cellsCross-linking of Fcε Receptors leads to

degranulationHanne Frøkiær

Kinetics of major biochemical events after IgEreceptor cross linking in mast cells Hanne Frøkiær

Hanne Frøkiær

Initiation of an allergic reaction

Second and later encounter with the allergen

Allergy:Exogenous factors affecting sensitation

� Exposure� Magnitude

� Frequency� Route

� Atmospheric pollution� Tobacco smoke

� Geographical factors

� Metals

� Detergents

Hanne Frøkiær

PrevalencePrevalence ofof food allergy food allergy depends ondepends on thethe climaclima and and agriculturalagricultural traditiontradition

Hanne Frøkiær

Worst case: anaphylactic shock Worst case: anaphylactic shock Hanne Frøkiær

Allergic symptoms to food Allergic symptoms to food

How muchHow much is to is to muchmuch??

Minimum dose of peanut protein thatelicited an allergic reaction:

1-5 mg protein (DBPCFC)

100 µg protein (single case)

Hanne Frøkiær

What is the problem?What is the problem?

1.How to avoid allergic reactions in sensitised individuals

2.Novel food

Hanne Frøkiær

How to avoid allergic reactions in sensitised individualsHow to avoid allergic reactions in sensitised individuals

1. Residual reactive allergens in processed food

2. Contamination from the processing plant

3. Cross-reactivity to other plant proteins

Hanne Frøkiær

Allergens in Allergens in processed foodprocessed food::

�Plant oils

�polysaccharides, (plants, shellfish)

�Emulsions

�Extensively heated products

�Hydrolysed products

Hanne Frøkiær

Allergen Allergen ExampleExample: Ara : Ara hIIhII

Major allergen in Major allergen in peanutspeanuts�Protease resistant�Heat resistant�Digested allergen can still react

Hanne Frøkiær

Lehmann et al. 2006

Allergen Allergen ExampleExample : Ara : Ara hIIhII

Major allergen in Major allergen in peanutspeanuts�Protease resistant�Heat resistant�Digested allergen can still react

Hanne Frøkiær

Lehmann et al. 2006

How to avoid allergic reactions in sensitised individualsHow to avoid allergic reactions in sensitised individuals

1. Residual reactive allergens in processed food

2. Contamination from the processing plant

3. Cross-reactivity to other plant proteins

Hanne Frøkiær

How to avoid allergic reactions in sensitised individualsHow to avoid allergic reactions in sensitised individuals

1. Residual reactive allergens in processed food

2. Contamination from the processing plant

3. Cross-reactivity to other plant proteins

Hanne Frøkiær

Prerequisites for cross allergenicity of two proteins: Hanne Frøkiær

More than one epitope in common

Common foods provoking food allergy Hanne Frøkiær

Food Cross reacting foods

Cows' milk Mares' milk, goats' milk, ewes' milk

Hens' eggs Eggs from other birds

Cod Mackerel, herring, plaice, etc

Shrimps Other crustaceans

PeanutsSoy beans, green beans, green peas,lupin

Soy beansSee above

Wheat Other grains, most often rye

Additives Mostly unknown (both synthetic and naturally occurring)

Hanne Frøkiær

Cross reactivity of allergens

How to handling the problems?How to handling the problems? Hanne Frøkiær

1. Labeling

2. Risk assessment of novel foods

3. Improved knowledge on relevant cross-reacting proteins

4. Improved knowledge on factors increasing the prevalenceof allergy