Supplementary Material for: IL-15 Expression Pattern in Atopic Dermatitis

Background: An increased expression of interleukin (IL)-15, a cytokine with a key role in stimulating innate and adaptive immune cells, such as dendritic cells (DC), natural killer cells, and T cells, has been observed in infectious and inflammatory diseases, including autoimmune diseases as well as cancer. Atopic dermatitis (AD) is a common inflammatory skin disease characterized by a type 2 immune response. Objective: To explore the expression of IL-15 and its pattern in AD skin. Method: Immunofluorescence staining was performed on skin specimens of AD skin, nonlesional AD skin (AD NL), and normal skin (NS) using antibodies directed against IL-15 and CD3, mast cell tryptase, eosinophil cationic protein, CD68, CD11b, CD1a, and vimentin. Results: A significantly higher IL-15 expression in AD and AD NL was observed in both the epidermis (p = 0.0003) and the dermis (p = 0.0154) as compared to NS. Cells expressing IL-15 were mainly keratinocytes, CD1a+ DC, CD11b+ DC, CD68+ macrophages, and vimentin+ fibroblasts. In AD, an increase in the relative numbers of IL-15 expressing CD1a+ DC, macrophages, and fibroblasts was noted. Conclusion: Our results demonstrate an expression of IL-15 in AD similar to that of eosinophilic esophagitis which is also a type 2 disease. IL-15 may serve as a therapeutic target for AD.