The skin is divided into three layers: (1) The epidermis, the outermost layer of skin, provides a waterproof barrier and creates the skin tone. Although the most abundant cells of the epidermis are keratinocytes, there are also nonepithelial immune cells present in the epidermis, such as Langerhans cells and dendritic epidermal T cells (DETCs). (2) The dermis, directly under the epidermis, contains tough connective tissue, hair follicles (HFs), and sweat glands. The dermis also hosts different subtypes of T cells that recirculate through skin-draining lymph nodes and are involved in normal immunity as well as inammatory skin diseases such as psoriasis (Bos et al., 1987; Streilein, 1983). In addition to T cells, the dermis is enriched with tissue macrophages and dendritic cells that originate from the yolk sac and self-renew within the skin under inammatory conditions (Jenkins, 2011). Together with cutaneous innate immune cells, the circulating monocytes.