CD8⁺ T cells in the lesional skin of atopic dermatitis and psoriasis patients are an important source of IFN-γ, IL-13, IL-17, and IL-22

Although CD4 + T cells are known to contribute to the pathology of atopic dermatitis (AD) and psoriasis, the role of CD8 + T cells in these diseases remains poorly characterized. The aim of this study was to characterize the cytokine production of T cells from AD and psoriasis skin. We found that CD4 + T cells isolated from AD skin were largely Th2 (T helper type 2) biased, in agreement with prior reports. However, we also observed large numbers of CD8 + T cells producing IL-13, IFN-γ, and IL-22. We observed increased numbers of CD8 + T cells isolated from AD skin, and immunohistochemistry studies confirmed the presence of CD8 + T cells in the dermis and epidermis of AD skin lesions. Surprisingly, T-cell cytokine production was similar in the lesional and nonlesional skin of patients with AD. T cells from psoriatic lesional skin predominantly produced IFN-γ, IL-17, and IL-22, in agreement with prior studies. However, in addition to Th17 cells, we observed high percentages of CD8 + T cells that produced both IL-22 and IL-17 in psoriatic skin lesions. Our findings demonstrate that CD8 + T cells are a significant and previously unappreciated source of inflammatory cytokine production in both AD and psoriasis.