The aim of the study was to standardize and evaluate technically optimized
food allergen extracts fbr use in skin prick test (SPT). The standardizatio
n procedure comprised 36 allergic histories in 32 food allergic patients wi
th 21 healthy, non-atopic individuals serving as controls. The patients had
a history of allergic symptoms upon ingestion of either cow's milk (n = 3)
, hen's egg (n = 9), wheat (n = 4), hazelnut (n = 14) or cod (n = 6). They
also had specific IgE in serum to the food in question and a positive SPT w
ith a fresh preparation of the food. The diagnosis had been confirmed by a
double-blind, placebo-controlled food challenge, except for the hazelnut-al
lergic patients. The controls were subjected to an open food challenge with
all the foods to ensure tolerance. The standardization was performed by me
ans of titrated SPT in accordance with the guidelines on biological standar
dization from the Nordic Council on Medicine. Regression analysis of the sk
in wheal areas was performed for each patient and the median protein concen
tration of allergen preparation (median C-h10) eliciting a wheal area of th
e same size as histamine 10 mg/ml was calculated. The median C-h10 was 0.56
mg/ml for milk, 0.88 mg/ml for egg, 5.4 mg/ml for wheat, 2.1 mg/ml for haz
elnut and 0.017 mg/ml for the cod extract. The sensitivity of the median C-
h10 estimated from the SPT data was 1 for milk, 0.98 for egg, 1 for wheat,
1 for hazelnut and 0.87 for the cod extract. The allergenic activity of the
hazelnut extract was further investigated by leukocyte histamine release (
HR) and immunoblotting experiments using sera from 27 hazelnut allergic pat
ients. The clinical sensitivity of the optimized hazelnut extract evaluated
by HR was 0.78 compared to 0.30 for a commercially available hazelnut extr
act (Soluprick). Immunoblotting results showed a stronger IgE binding capac
ity and additional IgE-binding bands of the optimized hazelnut extract comp
ared with the Soluprick extract. (C) 2001 Elsevier Science B.V. All rights
reserved.