Electron microscopic examination showed varying numbers of typical Langerhans cells in the dermis in normal human skin, pityriasis rosea, reticulum cell sarcoma, and Letterer-Siwe disease as well as among the stromal and parenchymal cells of several benign appendage tumors. Langerhans cells were observed crossing the basement membrane and an epidermal Langerhans cell in mitosis was seen. These findings suggest that Langerhans cells are not directly related to epidermal melanocytes and may constitute a self-perpetuating "intraepidermal phagocytic system" to which histiocytes from the dermis are added from time to time.
Hashimoto K, Tarnowski WM. Some New Aspects of the Langerhans Cell. Arch Dermatol. 1968;97(4):450-464. doi:10.1001/archderm.1968.01610100090015