Allergen


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An allergen is a substance that can trigger hypersensitivity reactions (allergic reactions) via the immune system . The different hypersensitivity reactions (allergies, pseudoallergies and intolerances ) are described in the article Allergy . This article describes the fabrics.

An allergen is an antigen . Allergens have no chemical properties in common. Because of this, it is not possible to develop a chemical that destroys allergens. Most allergens are proteins or protein compounds. The immune system of allergic patients react with the formation of IgE - antibodies to the contact with allergens. In contrast, “pseudoallergens” are substances in which the immune system is not involved, but mediators such as B. the histamines .

Allergens can be classified according to different aspects:

  • according to the type of contact with the allergens (e.g. inhalation allergens, food allergens)
  • after the allergen source (. e.g., animal hair allergens , pollen allergens , mold allergens )
  • according to the pathomechanism by which the allergic reaction is triggered (e.g. IgE-reactive allergens)
  • according to the frequency of their detection by IgE antibodies (major and minor allergens)
  • according to their amino acid sequence into certain allergen groups (e.g. group 5 grass pollen allergens) or into certain protein families (e.g. lipocalins , profilins ). Based on this classification, possible cross allergies can be read off.

IgE reactive allergens

IgE-reactive allergens are those antigens against which the misdirected immune response in type I allergies is directed. These allergens occur ubiquitously (everywhere) and everyone comes into contact with them, through inhalation , ingestion or contact. In healthy individuals, there is either no immune response to allergens or a mild immune response with the production of allergen-specific IgG 1 - and IgG 4 - antibodies . In contrast, allergy-specific IgE antibodies are formed in allergy sufferers . To put it simply, this altered immune response is attributed to a displaced T helper cell type 1 - type 2 (Th1-Th2) balance, with a Th2-dominated immune response in allergy sufferers and a Th1-dominated immune response in healthy people.

All IgE-reactive allergens have in common that they are very water-soluble and rather very stable proteins or glycoproteins. These are mostly small proteins between 5 and 80  kDa . Otherwise allergens are very different in terms of their structure, amino acid sequence or biological function. The question of “what makes an allergen an allergen” has not yet been answered satisfactorily. Various factors such as B. the type of allergen ingestion (e.g. by inhalation), the particle size, the enzymatic activity of some allergens and the fact that allergens are ingested in extremely small amounts (nanogram amounts are sufficient) seem to have an influence on allergenicity . All allergens have in common that they have to be taken up by dendritic cells and induce differentiation of the dendritic cell into a Th2-inducing activated dendritic cell.

IgE reactive allergens are found in a variety of allergen sources. One allergen source can release several different allergens. More than 20 different allergens are known for the house dust mite Dermatophagoides pteronyssinus . Allergy sufferers can be sensitized to just one allergen or to several allergens from one allergen source, i.e. they can form IgE antibodies. “Main allergens” are those allergens from an allergen source against which more than 50% of the patients with the allergy in question form IgE antibodies. All others are "minor allergens".

Contact allergens

Contact allergens trigger type IV allergies. The typical clinical picture is allergic contact eczema , which shows up precisely on the parts of the body that come into contact with the allergen in question. Usually these are the hands, face, lower legs or neck.

Among the most common contact allergens include nickel , thimerosal , perfume , cobalt , formaldehyde , Peru balsam , rosin , isothiazolinones , chromium , Thiuramix .

Contact allergens play a particularly important role in the professional environment. Occupational groups that are frequently affected are cooks, hairdressers, bakers, cleaners, staff in furniture manufacturing, in meat and fish processing companies and in gardening centers.

The EU Directive 94/27 / EC (“Nickel Directive”) stipulates that jewelry and other products that come into contact with the skin must not contain nickel.

Examples of contact allergens:

  • of animal origin: silk, wool , wool wax, mites
  • Vegetable origin: meadow plants and primroses
  • chemical contact allergens: tar , nickel and chromium

Inhalation allergens or aeroallergens

different pollen

Inhalation allergens or aeroallergens are absorbed through the breath. Birch pollen allergens are a typical example.

Examples of inhalation allergens:

  • of animal origin: house dust and animal hair
  • of vegetable origin: grass pollen, fungal spores, flour , wood flour and wood dust
  • chemical origin: Vapors from additives in fuels, plastics and coatings

Food allergens

Food and drug allergens enter the body through the mouth.

Examples of food and drug allergens:

  • animal origin: milk protein, eggs, crabs, fish and meat, mite cheese
  • vegetable origin: strawberries, apples, nuts, beans
  • Medicines: pain relievers and penicillin

It is very difficult and so far hardly successful to compare the allergy-inducing activity of different allergens with one another. Methods for allergen assessment were developed in the USA and Australia: The FDA uses the LOAEL (Lowest Observed Adverse Effect Level) assessment for food allergens . In addition, there are threshold values ​​for some allergens in ppm (mg protein per kg food) according to the VITAL concept ( Voluntary Incidental Trace Allergen Labeling , Australia).

According to the Food Labeling Ordinance , the use of certain (more frequent) allergen groups as ingredients in food must be declared.

Compilation of the LOAELs for food allergens published by the FDA in 2006
food LOAEL range (in mg protein)
egg 0.13 to 1.0
peanut 0.25 to 10
milk 0.36 to 3.6
Nuts (macadamia, cashew, almond, walnut, pistachio, hazelnut and others) 0.02 to 7.5
soy 88 to 522
fish 1 to 100
Threshold values ​​for some allergens in ppm (mg protein per kg food) according to the VITAL concept
Food Action level 1 Action level 2 Action level 3
milk <5 5-50 > 50
egg <2 2-20 > 20
soy <10 10-100 > 100
fish <20 20-200 > 200
peanut <2 2-20 > 20
hazelnut <2 2-20 > 20
Sesame seeds <2 2-20 > 20
Crustaceans <2 2-20 > 20
gluten <20 20-100 > 100

On the one hand, the above tables reveal contradictions in the assessment of the allergenic potential of various foods, which proves the problem of these quantifications. On the other hand, they provide a basis for comparing different foods with one another with regard to their allergenicity and for being able to estimate a rough ranking.

According to a study, food allergens such as milk components, hazelnuts, seafood , ovalbumin or fish allergens are completely digested in vitro by simulating acidic gastric digestion with pepsin within a few minutes, but not when the pH value is increased. The researchers concluded from this that food allergy problems could be related to an increased pH environment in the stomach. Infants only have gastric acid levels like adults at the end of their second year of life. People with reduced gastric acid secretion or who have taken antacids , sucralfate , H 2 -receptor blockers or proton pump inhibitors also have elevated gastric pH values.

Diagnosis

For allergy diagnostics in food, the ELISA can be used for the direct, quantitative determination of the allergen and the PCR for the indirect detection of the DNA of the allergen. PCR is often used in heavily processed foods, as DNA is significantly more heat-stable. In acidic foods where DNA can hydrolyze or where no effects on proteins are expected, the ELISA test is the method of choice. This is especially true for the detection of milk or eggs, which naturally contain little DNA and a lot of protein.

Injection allergens

Injection allergens enter the body through injections . This also includes insect venom allergies , in which the allergen is transmitted through insect bites.

Examples of injection allergens:

  • animal origin: bee venom, wasp venom, jellyfish venom
  • of fungal origin: drugs such as penicillins (from fungal cultures)
  • chemical origin: iodine-containing contrast media , novocaine and similar anesthetics, preservatives such as parabens

Lead allergens

Key allergens provide important information on the extent to which other substances can lead to an allergic reaction. In 50% of cases with a birch allergy , people with a cross allergy also react to certain foods such as apples and pears.

Declarable allergens

Pseudoallergens

Common airborne, non-allergic irritants ( pseudoallergens ) are:

Other triggers for allergy-like symptoms:

  • Contrast media
  • Medication (e.g. acetylsalicylic acid )
  • Milk sugar (lactose)
  • Food and luxury foods with a high histamine content
  • Anesthetics

Allergen-free substances

Guaranteed no allergies trigger:

Allergies have been described for workers who handle vitamin B1. Immediate-type allergies and delayed-type allergies have been described for the use of vitamin B12 in patients. Vitamin E, INCI tocopherol, can also trigger allergies in cosmetic products (used here as an antioxidant). However, these allergies are not common.

See also

Wiktionary: Allergen  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. Kirsten Beyer: Strategies for determining threshold values ​​for food allergens from a clinical point of view. Expert discussion within the framework of the BMELV conference 2008 "Allergies: Better information, higher quality of life" on October 15, 2008 in Berlin (PDF; 9.8 MB)
  2. BMEL: Allergen labeling on packaged foods is mandatory. Retrieved Feb 5, 2015.
  3. Susanne C. Diesner, Isabella Pali-Schöll, Erika Jenden-Jarolim, Eva Untersmayr: Mechanisms and risk factors for type 1 food allergies: the role of gastric digestion doi : 10.1007 / s10354-012-0154-4
  4. LADR informs: Allergens in food
  5. ^ Fisher: Contact Dermatitis. 4th edition. RL Rietschel, JF Fowler. Williams and Wilkins, Baltimore et al. a., pp. 151-152.

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