What is allergy

An allergy is the response of the body's immune system to normally harmless substances, such as pollens, foods, and house dust mite. Whilst in most people these substances (allergens) pose no problem, in allergic individuals their immune system identifies them as a 'threat' and produces an inappropriate response.1

Exposure to similar allergens leads to different patterns of allergic disease in children.2,3 This could result from different patterns of allergen entry. The skin acts as a barrier to allergen entry. Skin barrier defects, commonly present within the population, have been linked to more severe patterns of sensitisation and worse allergy-related disease. The presence of exposure to particular allergens can thus be related to symptoms through allergy testing and this will help distinguish between sensitised and non-sensitised individuals, thus offering directions for better management.3

Allergy affects approximately 50% of UK children (6 million)4 and approximately 44% of UK adults (21 million).5 Identifying allergies early can provide much needed answers for both patients and health care professionals and has been proven to reduce health care costs in asthma by more than half.

Adapted from: Hausmann O, et al. 2012.7

To take the RCGP Allergy module, click here.

Symptoms of allergy

The symptoms of allergy are vast and can often be confused with other conditions. Some common presentations of allergy include rhinitis, asthma, eczema, anaphylaxis, food allergy and occupational allergy. Within these conditions there are a number of symptoms which at first presentation may not necessarily be attributed to allergy, and as such may result in poor patient management.

Eczema

  • Abnormally dry skin
  • Dry depigmented patches
  • Erythrodermic rash
  • Itching
  • Oozing vesicles
  • Crusted vesicles
  • Eroded vesicles
  • Erythematous plaques
  • Lichenified, slightly pigemented, excoriated plaques
  • Exhaustion
  • Thick, pale excoriated plaques

Asthma

  • Wheezing
  • Breathlessness
  • Chest tightness
  • Coughing

Rhinitis

  • Stuffed-up nose
  • Runny nose
  • Post nasal drip
  • Red itching eyes
  • Watering eyes
  • Repeated sneezing
  • Headache
  • Nasal itching
  • Facial pain
  • Ear pain
  • Tiredness

Food Allergy

  • Mild symptoms
  • Itching in the mouth
  • Urticaria
  • Intense itching
  • Swelling of the face
  • Feeling very hot or cold
  • Rising anxiety
  • Pale/flushed appearance
  • Mild wheezing or cough
  • Abdominal pain
  • Nausea
  • Decreased level of consciousness
  • Diarrhoea
  • Severe symptoms
  • Difficulty in breathing
  • Wheezing
  • Hoarseness
  • Croupy/choking cough
  • Very pale/blue lips
  • Unresponsiveness
  • Collapse

Anaphylaxis

  • Shortness of breath
  • Wheeze
  • Swelling in the throat
  • Cough
  • Rhinitis
  • Nausea
  • Vomiting
  • Diarrhoea
  • Swelling of skin (lips and eyes)
  • Stomach pain
  • Urticaria
  • Flushed skin
  • Itch without rash
  • Loss of consciousness
  • Low blood pressure
  • Headache
  • Seizure
  • Substernal pain

Adapted from WAO white book, 2011 and NICE guidelines 2011.6,8

Allergy Diagnostics

What is specific IgE?

Specific IgE is a quantitative blood test and has an excellent clinical performance (Sensitivity 84-95% and specificity 85-94% depending on the allergen)

  • Can be used in any patient, irrespective of medication or condition, without risk of adverse reaction (anaphylaxis)
  • Does not require specialised equipment, training or facilities

How does ImmunoCAP™ work?

  • 1. The allergen, allergen component on the solid phase, reacts with the specific IgE in the patient serum sample.
  • 2. After washing away non-specific IgE, enzyme-labelled antibodies against IgE are added to form a complex.
  • 3. After incubation, unbound enzyme-labelled anti-IgE is washed away and the bound complex is then incubated with a developing agent.
  • 4. The higher the fluorescence, the more specific IgE is present in the sample.

Molecular allergy learning

Would you like to know more about allergen components and how they can improve the diagnosis of allergic patients?

Take a tour through our education module

Molecular Allergology Users's Guide

Download

What are components?

Every allergen source contains thousands of molecules, but only a few of these are allergenic. An allergen molecule, or component, is a single molecule recognised by allergen specific antibodies thereby causing an allergic reaction. An allergen source may have several allergen components which all have different characteristics. Molecular allergy seeks to identify those specific components and so provide a clear understanding of how the allergic reaction is caused.

IgE antibodies are formed as a direct response to each allergen component.

Most allergen components are specific to the allergen source, but some are 'cross-reactive', meaning they are structurally similar to allergen components in other allergen sources.

For instance the Ara h 8 PR-10 protein found in peanuts, is very similar to the Bet v 1 PR-10 protein, the most common allergen in Birch pollen.

What are the clinical benefits of testing for components?

Allergen component diagnostics measure IgE to particular allergen components, uncovering additional information about an underlying allergy.

Not only do the indicate specific allergen reactivity in the way that whole extracts do but they are also indicators for:

Understanding patient risk - add confidence to your assessment

Selecting patients for immunotherapy - useful for venom and aero allergy patient selection

Understanding cross-reactions between species - help to understand multiple sensitisations e.g. in pollen-food syndrome

Molecular allergy guidebooks

The molecular allergy guidebooks have been designed to:

  • Help you understand the principles of molecular allergy
  • Help you determine which components you need to test for
  • Help you interpret the results

Go Molecular! Molecular allergy the basics

A short overview of the important themes within molecular allergy, especially protein families, their clinical relevance and nomenclature. Download

Go Molecular! The allergen components

A straightforward summary helping you select components and interpret results for the most common allergens. Download

The guidebooks are quick to use and will assist you in making an informed diagnosis

How do I interpret results?

The presence of allergen-specific IgE is usually a risk of allergy symptoms and a result ≥0.1 kUA/L indicates sensitisation. Traditionally, the higher the IgE level the greater the risk.

Some molecular allergens are associated with a higher risk for systemic reactions, whilst some allergens are considered no or a very low risk for severe reactions. A high level IgE to a high-risk allergen such as Ara h 2 or Cor a 9 would often carry a high risk for patients.

Always consider tests results in association with a clinical history.

Plant component families

Plant component families are shared between species; the close the species are related the more similar the components can be.

This increases the potential for IgE molecules directed against pollen allergen epitopes in food. There are five main types of plant component groups indicated in allergy. These are PR-10 (pathogenesis related family number 10), profilin, nsLTPs (non-specific lipid transfer proteins), storage proteins and CCDs (cross-reactive carbohydrate determinants):

Protein family Risk for systemic reactions? Do I have to consider many different allergen sources?
Storage proteins Yes. Storage proteins heat and digestion stable which explains their ability to move often cause systemic reaction in addition to OAS (oral allergy syndrome). No. Storage proteins are not cross-reactive, except for very closely related allergen sources (e.g. between legumes such as soy and peanut).
nsLTPs Yes. nsLTPs are heat and digestion stable which explains their ability to more often cause systmic reaction in addition to OAS. Yes. Partly cross-reactive (the degree of structural similarity varies between nsLTPs in plant food and pollen).
PR-10s Low. Often cause only local symptoms such as OAS due to their sensitivity to heat and digestion, but a few cases with systemic reactions have been reported e.g. for soy Gly m 4 and Celery Api g 1. Yes. Partly cross-reactive (the degree of structural similarity varies between PR-10s in plant food and pollen).
Profilin Low. Often have little clinical relevance in allergic diseases. However, profilins may cause local reactions in some patients allergic to plant foods including citrus fruits, banana and tomato, and a few cases with systemic reactions have been reported e.g. for melon and lychee. Yes. Highly cross-reactive (the degree of structural similarity varies between nsLTPs in plant food and birch-related pollen).
CCDs Very low. Usually not associated with clinical reactions but may induce IgE antibody responses in some patients. Yes. Highly cross-reactive (same CCD structure in pollen, plant food and venoms).
Protein family Storage proteins
Risk for systemic reactions? Yes. Storage proteins heat and digestion stable which explains their ability to move often cause systemic reaction in addition to OAS (oral allergy syndrome).
Do I have to consider many different allergen sources? No. Storage proteins are not cross-reactive, except for very closely related allergen sources (e.g. between legumes such as soy and peanut).
Protein family nsLTPs
Risk for systemic reactions? Yes. nsLTPs are heat and digestion stable which ex-plains their ability to more often cause systmic reaction in addition to OAS.
Do I have to consider many different allergen sources? Yes. Partly cross-reactive (the degree of structural similarity varies between nsLTPs in plant food and pollen).
Protein family PR-10s
Risk for systemic reactions? Low. Often cause only local symptoms such as OAS due to their sensitivity to heat and digestion, but a few cases with systemic reactions have been reported e.g. for soy Gly m 4 and Celery Api g 1.
Do I have to consider many different allergen sources? Yes. Partly cross-reactive (the degree of structural similarity varies between nsLTPs in plant food and pollen).
Protein family Profilin
Risk for systemic reactions? Low. Often have little clinical relevance in allergic diseases. However, profilins may cause local reactions in some patients allergic to plant foods including citrus fruits, banana and tomato, and a few cases with systemic reactions have been reported e.g. for melon and lychee.
Do I have to consider many different allergen sources? Yes. Highly cross-reactive (the degree of structural similarity varies between PR-10 in plant food and birch-related pollen).
Protein family CCDs
Risk for systemic reactions? Very low. Usually not associated with clinical reactions but may induce IgE antibody responses in some patients.
Do I have to consider many different allergen sources? Yes. Highly cross-reactive (same CCD structure in pollen, plant food and venoms).


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References
  1. Allergy UK. Available from https://www.allergyuk.org/what-is-an-allergy/what-is-an-allergy last accessed September 2015.
  2. Palmer CN, et al. Nat Genet, 2006;38(4):441-446.
  3. Basu K, et al. Allergy 2008;63(9):1211-1217.
  4. Punekar YS and Sheikh A. Clin Exp Allergy 2009; 39: 1889-1895.
  5. Mintel Oxygen Reports. Not to be sneezed at- almost half of all Brits are allergy sufferers. 2010. Available from www.mintel.com/press-centre/press-releases/512/not-to-be-sneezed-at-almost-half-of-all-brits-are-allergy-sufferers: last accessed April 2013.
  6. Pawankar (Ed) et al. White book on allergy 2011; World Allergy Organisation UK.
  7. Hausmann O, et al. Chem Immunol Allergy 2012;97:32-46.
  8. National Institute for Health and Clinical Excellence. Food allergy in children and young people (CG116). 2011. London: National Institute for Health and Clinical Excellence.

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