• atopic dermatitis;
  • atopy patch test;
  • house dust mite;
  • immunoglobulin E;
  • immunohistochemistry

Background:  The eczema reaction in the atopy patch test (APT) is proposed to be immunoglobulin (Ig)E mediated, but can take place also in individuals lacking allergen-specific IgE in serum. The purpose of this study was to evaluate the importance of allergen-specific serum IgE for the APT reaction.

Methods:  Ten patients with reproducible positive APT to extract of Dermatophagoides pteronyssinus, five patients with (group A) and five patients without (group B) detectable serum-IgE to D. pteronyssinus, were tested with extract of D. pteronyssinus on normal skin for 6, 24, 48 and 72 h. Skin biopsies were taken and analysed for cell infiltrates, eosinophils (EG2), IgE, FcɛRI, CD1a, CD4, CD8 and metalloproteinase 9 (MMP9).

Results:  The number of IgE+, CD4+, EG2+ and MMP9+ cells increased with time in group A. FcɛRI+ cells and CD8+ cells increased with time in both groups. A correlation was found between the levels of D. pteronyssinus-specific serum-IgE and the score of dermal cell infiltrates at 72 h. The three patients with the highest values of allergen-specific IgE also had the highest expression of EG2+ cells and the highest APT scores.

Conclusions:  Our study strengthens the hypothesis that the IgE molecule has a key role, at least as an amplifier, in the APT reaction.