INTRODUCTION
In Europe, the prevalence of allergic asthma (8%) and rhinitis (25%)
is high with still increasing trend in the last
decades.1
The diagnosis of pollen allergy used to be mainly based on medical
history, skin prick test (SPT) and the detection of allergen-specific
serum IgE by using pollen extracts. Pollen seasons from distinct plants
may overlap, and pan-allergens contained in various pollen may cause
IgE-cross-reactions, though. Therefore, molecular allergy diagnosis (MD)
assessing IgE reactivity to so-called marker allergens has increasingly
gained importance in recent years. However, the question whether MD may
improve extract-based diagnosis and help with the decision for
allergen-specific immunotherapy (AIT) has not been clarified
yet.2,3
More than 90% of patients with grass pollen allergy show IgE antibodies
against Phl p 1 and Phl p 5,4 and more than 95% of
birch allergic patients are sensitized to the major allergen Bet v
1.5 Ash tree is another allergen of increasing
relevance in Central-Europe.6 The distinction between
birch and ash tree allergy is relevant for the decision which AIT is
suitable. However, both pollen seasons overlap in Austria causing
concomitant allergic symptoms to either tree species.8In MD the structurally homologous Ole e 1 from olive tree is usually
used instead of the major ash tree allergen Fra e 1 which is not
commercially available.7
The defensin-like protein Art v 1 is the single major allergen in
mugwort pollen, recognized by IgE antibodies from 90% of patients with
mugwort allergy.9 About 10-14% of patients with
rhinoconjunctivitis in Eastern Austria suffer from mugwort
allergy.10 With the mugwort season in eastern Austria
overlapping with that of the ragweed season, differentiation based
exclusively on patients’ history is difficult.8Ragweed has gained increasing interest, not only in Eastern, but also in
Central Europe. The major allergen available for genuine ragweed allergy
is Amb a 1, a pectate lyase with about 50% sensitization rates in
ambrosia allergic patients.11
Cross-reactivity between mugwort and ragweed extract often leads to
inconclusive results. For example, Amb a 1 and Art v 6 as well as Amb a
4 and Art v 1 show structural homologies,12 however,
only Amb a 1 and Art v 1 offer clinical importance for pollen allergic
patients. Also, in this case it is important to discriminate between
both weed allergies, especially if one has to decide which AIT has to be
applied.
The aim of this study was to evaluate whether the use of the major
pollen-allergens (Phl p 1+5, Bet v 1, Ole e 1, Art v 1, Amb a 1) can
increase the diagnostic accuracy in patients with a single-sensitization
against grass, birch, ash, mugwort or ragweed pollen. If there was a
discrepancy in the results of extract and major-allergen, we reviewed
medical charts to see if this knowledge changed medical recommendations
for AIT.
In addition, we intended to analyze how many patients were
double-sensitized to birch and ash-tree and/or to mugwort and ragweed,
respectively and if this double-sensitization was caused by extracts´
cross-reactivity or was based on a relevant sensitization against one or
both major allergens.
The study was part of a diploma thesis (C.H.) at the Medical University
Vienna, Austria.13