Morphologic and morphometric study of the two main cell lineages involved in mycosis fungoides: the lymphoid cells and the Langerhans cells.

A comparative light and electron microscopic study was carried out on skin biopsies from 5 mycosis fungoides patients (stages II and III). In addition, certain zinc-iodide-osmium (ZIO) procedures that selectively reveal the Langerhans cells (LC) were also applied. Several morphometric analyses, such as relative frequency, cell size, nuclear:cell ratios and nuclear contour indexes, were performed. Two main cell lineages were found in the dermal infiltrate: the lymphoid cells, represented by lymphoblastlike cells (LB), lymphocytes (L), and mycosis fungoides cells (MFC), and the Langerhans cells. A pattern of cellular organization of the dermal infiltrate was recognized. The LC appeared as the "organizing" cell. The morphometric study indicated that all LB, L, and MFC have the chance, at the same time, to be in contact with a LC. The application of the ZIO procedures clearly indicated a "translocation" of the LC, since they were scarce or absent from the epidermis and numerous in the dermis. Evidence is presented indicating that differentiation of LB into L and malignant transformation of L into MFC are processes occurring predominantly in the dermis. It is postulated that in the chronic stages of mycosis fungoides, L-LC contacts occur mainly in the dermis and not in the epidermis and that the development of malignant clones may occur in the dermis.