Purified Der p1 and p2 patch tests in patients with atopic dermatitis: evidence for both allergenicity and...

Atopic dermatitis has many similarities with allergic contact dermatitis. Previous studies have revealed delayed-type allergic reactions indicating specific cell-mediated immune reactions in subgroups of patients. It has recently been recognized that purified house dust mite major allergens, Der p1 and Der p2 from Dermatophagoides pteronyssinus, exhibit a proteolytic enzyme activity similar to papain and maybe serine proteases (e.g. trypsin), respectively. This opens the possibility that house dust mites apart from an allergic epitope could elicit irritant reactions in atopic skin. We examined cutaneous reactivity to the purified proteins of house dust mite antigens, Der p1 and Der p2, in 36 consecutive patients with atopic dermatitis. We also patch-tested with trypsin and papain, in order to see if these proteolytic enzymes could induce irritant reactions. Twelve patients had type 1 allergy to Der p1 and two of these had type IV reactivity to D. pteronyssinus extract. Positive reactions were observed in another four patients, but they had also irritant reactions to papain and trypsin, indicating that the enzymatic activity may have elicited the reactions. The cutaneous reactivity was not linked to total serum IgE, but the patients with specific allergic patch tests had type I reactions to D. pteronyssinus extract. Our observations indicate that allergic patch tests towards Der p1 and p2 are rare and that irritant reactions from D. pteronyssinus proteolytic activity may be a more common phenomenon when patch-testing atopic dermatitis patients with house dust mite antigen extract.