Immunohistochemical studies in mite antigen-induced patch test sites in atopic dermatitis

The role of mite allergen in atopic dermatitis is still unclear. In this study, we investigated whether an eczematous reaction could be induced by patch testing with dust mite antigen. We succeeded in reproducing an eczematous lesion and the mite RAST-positive AD group showed a positive reaction much more than the RAST-negative group. Many mite antigen-bearing Langerhans cells, also possessing IgE molecules, were found by the use of an immuno-double labelling technique. By using immunoelectron microscopy, it was observed that the mite antigens were trapped by some macrophages, which were apposed to lymphocytes. To investigate the time-course of the reaction, the patch test reactions were read and biopsied after 1 h, 6 h, 24 h and 48 h. An eczematous reaction developed 24 h after patch testing. The mite antigen-bearing Langerhans cells were seen exclusively in the epidermis after 6 h, and mainly in the dermis after 24 h and 48 h. These results suggested that IgE-mediated contact hypersensitivity to mite antigen may develop and play an important role in AD.