Inverse correlation of domestic exposure to Dermatophagoides pteronyssinusantigen patch test reactivity in patients with atopic dermatitis

Background In recent years considerable interest in the pathogenetic role o f aeroallergens exacerbating atopic dermatitis (AD) has emerged. The 'atopy patch test' with aeroallergens was introduced by Platts-Mills et nl. as an experimental model and as a diagnostic tool. However, its relevance for th e clinical manifestation of AD is still not clear. Objective We asked whether there is a relationship between the individual a ntigen exposure to the major allergen of Dermatophagoides pteronyssinus (De r p 1) and the immunological markers of sensitization to Der p I or the cli nical severity of AD. Methods We investigated 92 patients with moderate to severe AD. For clinica l evaluation the SCORAD severity score was used. Patch tests were performed with purified Der p 1. Specific IgE was measured by a commercial assay. De r p 1 exposure was quantified in a sample of the patient's mattress dust by using a commercial ELISA. Results No correlation between SCORAD, Der p 1 exposure and PAST could be e stablished. However, there was an unexpected significant inverse correlatio n between the quantity of mite antigen in the mattress dust and patch test reactivity. Patients with a high antigen load (> 25 mu g/g) mostly had a ne gative patch test. Also, when Der p 1 was correlated to the mattress area ( m(2)) in this group all patch tests were negative. A possible explanation c ould be that continuous exposure of the skin to house dust mite allergen De r p 1 may induce a down-regulation of the skin immune system of patients wi th AD. Conclusion Although the mechanism of this phenomenon is presently unknown, our study shows that a positive allergen patch test alone should not be an indication to undertake allergen exclusion measures in AD patients.