Molecular allergy diagnostics

Specific allergy diagnostics with recombinantly produced or purified (glyco-) proteins. The analysis of specific IgE (sIgE) against single allergens can be performed individually in a singleplex procedure or, since 2001, multiplexed in a multiplex procedure.

Advances in molecular allergy diagnostics and chip-based microarray technology have made it possible to develop multiplex procedures with which the sIgE profile of a patient can be analysed in detail at the single molecule level.

For a balanced clinical interpretation of an allergological test result it is of great importance to distinguish between genuine sensitization and cross-reactivity. In pollen-allergic patients, who have, for example, a serological and/or skin reactivity to different allergens, it is important to distinguish between genuine sensitization and cross-reactivity. In pollen-allergic patients with serological and/or skin reactivity to different pollen species (e.g. grasses, birch, mugwort) this constellation may indicate either genuine sensitization or cross-reactivity to so-called cross-reactive panallergens. Such panallergens are for example: profilins (e.g. Bet v 2, Phl p 12, Amb a 8 and others), polcalcins (e.g. Bet v 4, Phl p 12 and others) storage proteins (e.g. Cor a 9, Jug r 1, Ana o 1, Pis v 1 and others) or lipid transfer proteins (e.g. Pru p 3, Cor a 8 and others).

The differentiation between genuine sensitization and cross-reactivity is only possible if the detection of IgE-reactivity to specific marker allergens (main allergens) is successful. Only then is a genuine primary sensitization present. Such a differentiation allows a differentiated verodnugation behaviour during allergen-specific immunotherapy (see SCIT below).

Smallest amounts (picogram range) of different allergens are coupled to a solid phase. This protein microarray (allergen chip) can then be used to determine the sIgE. In contrast to a single test and traditional extract-based allergen diagnostics, the multiplex method provides a comprehensive (with e.g. 100 allergens) sensitization profile at the single molecule level. This differentiated analysis allows a reliable statement of the individual sensitization profile.

The test system is currently manufactured and distributed by only one company (Phadia/Thermo-Fisher Scientific) under the product name ImmunoCap ISAC 112 (currently 112 single molecules from 51 animal and plant allergen sources). Further multiplex systems are in development.

The lower detection limit (LoD), defined as the lowest IgE concentration that can be reliably determined, was determined for 8 representative allergens (Ara h 1, Bet v 1, Der p 1, Equ c 1, Fel d 1, Gad c 1, Gal d 1, Phl p 5) and was between 0.05 and 0.28 ISU-E. It was determined with <0.3 ISU-E for all allergens.

1. Jakob T et al (2015) Molecular allergy diagnostics in multiplex procedure. Allergo J Int 24: 42-54