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ImmunoCAP® ISAC IgE Allergy Profile

Next to the prick test, the determination of allergen-specific IgE antibodies in serum has a key role in the detection of type I allergies. Typically, the CAP test (Thermo Fisher Scientific), which quantifies allergen-specific IgE antibodies in serum and permits the results’ allocation to CAP classes from 1 to 6, is performed in this context. While the IgE detection using CAP test allows for the simultaneous determination of only a limited number of allergens, the ImmunoCAP®ISAC (Thermo Fisher Scientific) enables the concurrent analysis of 112 allergen components from 51 different allergen sources. Thus, this test facilitates the determination of a comprehensive specific IgE antibody profile. However, the essential difference with regard to the CAP test is that the ISAC assesses only IgE antibodies against relevant allergen components. In contrast to skin tests and classic specific IgE determination, native allergen extracts are not utilised. Therefore, results from the ISAC test differentiate between genuine primary sensitisations and cross-reactions. This additional information allows a better risk assessment regarding clinical manifestations. Contrary to common believe, allergen component diagnostics (molecular allergen diagnostics) is not more sensitive than the common CAP test. Therefore, this test has not to be considered as a classic screening test, but is a powerful tool for differential diagnostics for patients with polysensitisations.

Significant clinical indications for the ImmunoCAP®ISAC IgE allergy profile are:

  1. Distinction between «only cross-reactivity« and genuine species-specific sensitisation
  2. Identification of potential risks for reactions and type of reaction regarding certain allergic sensitisations
  3. Assistance in the therapy and dietary selection, especially for patients with polysensitisations and positive IgE or prick test results regarding pollen-associated foods.

For targeted inquiries (e.g. clarification of relevance of peanut allergies, differentiation of bee and wasp venom allergies), the IgE CAP test can still be applied. For these inquieries, allergen component tests are available and German statutory health insurance companies do cover the costs. Due to the large allergen spectrum and the small required sample size, this analysis is especially suitable for allergy diagnostics in children.

Method

ImmunoCAP®ISAC is a biochip-based semi-quantitative immunoassay (Fig. 1). Allergen components are immobilized on the biochip and react with specific IgE from the patient’s sample. Bound IgE antibodies are determined with the help of fluorescence technique. Test results are issued in ISAC Standardized Units (ISU) and indicate the specific IgE level. For allergens included in the test, please consult the enclosed list.

Fig. 1  With the help of fluorescent spots on the biochip, the reaction of allergens and IgE antibodies is evaluated. The intensity of the signals is proportional to the number of IgE antibodies bound to the allergen.

The principles of Molecular Allergy Diagnostics

Contrary to the prick test or conventional allergy IgE diagnostics, which are based on allergen extracts, molecular allergen diagnostics focus on sensitizations against single allergen components (Fig. 2). Those allergen components are either obtained from allergen extracts (native allergen components, labelled with «n«, like in nMUXF3) or are produced in the recombinant manner (labelled with «r«, like in rApi m 1). These components can be allocated to different protein groups and allow the discrimination of the detected sensitizations as well as the reaction’s specificity. Table 1 on page 2 provides an overview of protein groups that are most frequently involved in allergies.

Fig. 2 Any source of allergens is composed of different specific and crossreactive allergen components. During the ISAC, they are evaluated individually and separately

Tab. 1 Protein groups most frequently involved in allergies and their characteristics

Protein groupRisk of anaphylactic reactionsRisk of anaphylactic reactionsCross-reactivityExample
Storage proteins+++++++++Ara h 1,2,3,6 (Peanut)
Cor a 9 (Hazelnut)
Jug r1,2 (Walnut)
Lipid transfer proteins++++++++Ara h 9 (Peanut)
Pru p 3 (Peach)
Jug r 3 (Walnut)
PR-10 protein+++++++Bet v 1 (Birch)
Gly m 4 (Soy Bean)
Pru p 1 (Peach)
Profilins++++++Bet v 2 (Birch)
Phl p 12 (Timothy grass)
Hev b 8 (Latex)

 (+ low, .... ++++ high marked) 

Advantages of the ISAC IgE Allergen Profile in comparison to specific IgE Diagnostics or Prick Test

  1.  Differentiation between real sensitizations and crossreactions in order to assess the risk of anaphylactic reactions and for optimal treatment planning.
  2. In cases of poly-sensitizations, it facilitates a comprehensive single stage assessment of the sensitization’s pattern.

The results for all allergens are presented in a commented medical report.

Material

200 μl serum (whole blood)

Request: ISAC IgE allergen profile

Costs

Please obtain the costs for the analysis  from the pdf-document

Literature

  1.  Allergen microarrays: a novel tool for high-resolution IgE profiling in adults with atopic dermatitis Ott H. et al. European Journal of Dermatology, 2010, 20 (1), 1-8
  2. The ImmunoCAP ISAC molecular allergology approach in adult multisensitized Italian patients with respiratory symptoms. Melioli G et al.Clin Biochem 2011, 44(12), 1005-11
  3. A new tool in the field of in-vitro diagnosis of allergy: preliminary results in the comparision of ImmunoCAP 250 with the ImmunoCap ISAC, Gadisseur R et al. Clin CHem Lab Med 2011, 49(2), 277-280
  4. Microarray of allergenic component-based diagnosis in food allergy. Sanz et al. Current Opinion in Allergy and Clinical Immunology 2011, 11, 204-209 8