Search

Human resident memory regulatory T cells (Tregs) exist in the normal, noninflamed skin. Except one, all previous studies analyzed skin Tregs using full-thickness human skin. Considering that thick dermis contains more Tregs than thin epidermis, the current understanding of skin Tregs might be biased toward dermal Tregs. Therefore, we sought to determine the phenotype and function of human epidermal and epithelial Tregs. Human epidermis and epithelium were allowed to float on a medium without adding any exogenous cytokines and stimulations for two days and then emigrants from the explants were analyzed. Foxp3 was selectively expressed in CD4+CD103− T cells in the various human epithelia, as it is highly demethylated. CD4+CD103−Foxp3+ cells suppressed proliferation of other resident memory T cells. The generation and maintenance of epithelial Tregs were independent of hair density and Langerhans cells. Collectively, immune-suppressive CD4+CD103−Foxp3+ Tregs are present in the normal, noninflamed human epidermis and mucosal epithelia.

Tissue-resident memory T cells exist in both the epidermis and the dermis in human skin. To analyze these cells, the skin needs to be incubated with dispase II to separate the two layers, that is, the epidermis and the dermis. The next step varies among researchers; the subsequent enzymatic digestion of the two layers is popular, whereas the spontaneous migration method can also be done. Scraping of these layers to yield skin T cells may reduce antigen modulation. This study aimed to determine each method's limitations. Dispase II incubation itself cleaves T-cell antigens. Therefore, further enzymatic digestion with collagenases strongly cleaves antigens. The scraping method yields skin T cells that are affected by dispase II as it is. However, skin T-cell yield is low. The spontaneous migration method recovers and/or upregulates antigens with T-cell activation and loses ∼20% of T cells in the floating sheets. However, there was no prominent bias regarding CD103 expression between emigrants and the remaining T cells in the sheets. There were 10