Increased Expression of Interleukin-12 in Lesional Skin of Atopic Dermatitis Patients with Psoriasiform Features on Histopathology: An Immunohistochemical Study

Background: Based on clinical and genetic differences, atopic dermatitis (AD) and psoriasis have been classified in two different diseases, but recently, some authors regarded them as in one spectrum. The histological similarities including epidermal hyperplasia between chronic stages of AD and psoriasis supports the presence of two diseases in one spectrum. Objective: We investigated clinical and immunohistopathological characteristics of adult Korean patients with AD showing psoriasiform chronic dermatitis on histopathology. Methods: In total, 59 Korean patients with chronic AD were enrolled. Clinical, laboratory, and histopathological features were compared between AD patients with psoriasiform features and those with non-psoriasiform chronic dermatitis features on histology. In addition, immunohistopathological characteristics were analyzed using antibodies for key regulatory and effector cytokines in psoriasis. Results: Fifteen patients (25.4%) showed a more psoriasiform histological appearance. The lesions in patients with psoriasiform features often showed clearer boundaries and noticeable scaling. The interleukin (IL)-23 expression in the psoriasiform chronic dermatitis group was not different from that in the psoriasis group, but the IL-17 expression was less than that in the psoriasis group. In the case of IL-12, multiple dermal inflammatory cells with dendrites were stained in the psoriasiform chronic dermatitis group compared with the 2 other non-psoriasiform subgroups. Conclusion: The results suggest that IL-12 secreted from dermal inflammatory cells might be one of the important factors associated with the formation of psoriasiform features in chronic AD. However, further studies are required to better define the specific role of IL-12.