Immunophenotyping of inflammatory cells in lesional skin of the extrinsic and intrinsic types of atopic dermatitis

Background There is a subgroup of atopic dermatitis (AD) patients with normal total and specific IgE levels and negative skin tests towards common allergens. This form of the disease has been referred to as the 'intrinsic' form of AD. Although previous studies have demonstrated differences in the cytokine profile between the extrinsic and intrinsic subtypes, the pathogenesis of both subtypes of AD remains unclear. Objectives To compare the inflammatory micromilieu in both forms of AD. Methods Immunophenotyping of the inflammatory cells was performed in lesional and nonlesional skin from 18 patients with extrinsic and 17 with intrinsic AD. Results Immunohistochemical analysis revealed a high proportion of CD4+ T cells in the dermis, with a similar CD4/CD8 ratio in the two groups. The expression levels of other T-cell markers and epidermal Langerhans cells were increased in both forms of AD. Although the T-cell repertoires in the two subtypes were similar, dermal infiltration of eosinophils and eosinophil granular proteins was more prominent in the extrinsic type than in the intrinsic type. Eotaxin immunoreactivity was also significantly higher in the extrinsic subtype. Conclusions The data suggest that although the overall inflammatory microenvironment in the two subtypes appears to be similar, differences in T-cell cytokine production might contribute to the differential tissue eosinophilia in these subtypes.