In vitro and in vivo characterization of hazelnut skin prick test extracts.

Rationale: Hazelnut allergy ranks among the most frequently observed food allergies. Clinical symptoms range from the oral allergy syndrome to life threatening anaphylaxis. Diagnosis of hazelnut allergy partially relies on in vivo testing by means of skin prick testing (SPT). The aim of this study was to characterize hazelnut SPT extracts both in vitro and in vivo.

Methods: Hazelnut SPT extracts were investigated for protein concentration and composition. The major hazelnut allergen Cor a 1, lipid transfer protein (LTP) and thaumatin-like-protein (TLP) were monitored by competitive RIA and immunoblotting. SPT extracts (n = 6) were analyzed for skin reactivity and the correlation between the SPT extract protein concentration and the mean skin reactivity (HEIC) was determined in a group of hazelnut-allergic patients (n = 30). For one SPT extract, the threshold level for Cor a 1 was determined in Cor a 1-monosensitized patients (n = 5).

Results: Protein concentrations ranged from 0.2-14 mg/ml. Although some proteins were present in most extracts (bands at 10, 22-28, 32 and around 48 kDa), clear differences in composition were observed (both intra- and inter-variability). The concentration of the major hazelnut allergen Cor a 1 differed up to a factor 50 (0.6-32 micrograms/ml). LTP was virtually absent in 3/9 SPT extracts and variable quantities of TLP were detected by immunoblotting. Some patients (6/30) had a false-negative SPT with 3/6 SPT extracts. There was a clear correlation between the protein concentration and the mean HEIC (RPearson = 0.87). The threshold level for Cor a 1 was +/- 3.2 ng/ml as assessed with one of the products investigated.

Conclusions: Heterogeneous protein concentration/composition of SPT extracts results in variable skin test responses. The absence of potentially severe allergens like LTP may lead to false-negative SPT results that jeopardize a patient's safety. From these results it can be concluded that there is a strong need for standardization of products for SPT.