CD4+ and CD8+ skin-associated T lymphocytes in canine atopic dermatitis produce interleukin-13, interleukin-22 and interferon-γ and contain a CD25+FoxP3+ subset

Background: T Cells play a major role in the immunopathogenesis of canine atopic dermatitis (cAD). However, the significance of cutaneous regulatory T cells (Tregs) and CD8+ T cells is currently unclear. Hypothesis/Objectives: The study aimed to evaluate the presence and distribution of Tregs in cAD and healthy skin and to determine the cytokine production of cutaneous CD4+ and CD8+ T cells. Animals: Biopsies were taken from four dogs with cAD (lesional and nonlesional skin) and four healthy control dogs. Methods: Distribution patterns of T-cell subtypes in cAD lesional, nonlesional and control skin were evaluated by immunohistochemistry. Phenotypic characterization of T cells from skin explant cultures and enzymatic digestions was performed using flow cytometry. Cytokine production of sorted CD4+ and CD8+ explant-derived T cells was measured by RT-qPCR. Results: Regulatory T cells phenotypically characterized by CD25+FoxP3+ were found in both CD4+ and CD8+ subsets of skin explant and digestion samples. The percentages of CD4+CD25+ cells that were FoxP3+ were similar in cAD and control skin. In atopic lesional and nonlesional explant samples, lower FoxP3+ percentages of CD8+CD25+ cells were seen compared with control skin. The presence of predominantly periadnexal CD25+FoxP3+ cells was confirmed by immunohistochemistry in lesional, nonlesional and control skin. The CD4+/CD8+ ratio was less than one in cAD skin with both skin explant and digestion methods. CD4+ and CD8+ T-cell subsets of lesional and nonlesional cAD skin were capable of producing interleukin-13, interleukin-22 and interferon-γ. Conclusions and clinical importance: Both CD4+ and CD8+ T cells are likely to contribute to the immunopathogenesis of cAD through the production of interleukin-13, interleukin-22 and interferon-γ. In both subsets, functional analysis of FoxP3+ cells is essential to determine their role.