Immunohistochemical studies on dust mite antigen in positive reaction site of patch test

We demonstrated that eczematous reactions could be induced by patch testing with mite antigens in the majority of patients with atopic dermatitis (AD). By using immuno-double labelling technique, many mite antigen-bearing Langerhans cells were seen in the epidermis in the early stage of the patch testing. Twenty-four hours later, these cells were observed only in the deep dermis. Immunoelectron microscopically, it was found that the mite antigens were trapped by macrophages, which were apposing lymphocytes. On the other hand, we observed that Langerhans cells and Leu 3a positive cells in the AD lesions carried IgE molecules. Furthermore, many IgE-positive dendritic cells bearing mite antigen were seen in the positive patch testing sites. Taken together, IgE-mediated contact hypersensitivity to mite antigen may play an important role in the pathogenesis of AD.