Further Evidence for the Self-Reproducing Capacity of Langerhans Cells in Human Skin

The limited number of Langerhans cells (LC) in the epidermis is one of the main reasons for the technical difficulties in resolving the question of LC kinetics in the present paper, we describe a method to evaluate the LC replication Potential in epidermis The procedure is based on the specific incorporation of bromodeoxyuridine (BrdU), a thymidine analogue, into the DNA during the S-phase of the cell cycle Mice, bearing human skin grafts, were injected s.c. every 6h for up to 17 days with BrdU. At different times, the incorporated BrdU as well as the human epidermal LC were revealed on skin sections using anti-BrdU and OKT-6 monoclonal antibodies, respectively. After 6h, 4. 9% of the LC were labeled with BrdU. Then, the number of OKT-6(+) BrdU(+) cells increased in a linear manner and achieved 34% at 120h, 67% at 240h, and 94% at 400h during the, course of continuous labeling procedures. Based on this result we calculated a total cell cycle time of 392h (16.3 days) and 12h for the S-phase for human epidermal LC.Applying this technique, we were able to show also that 48h after local treatment with 12-O-tretradecanoylphorbol-13-acetate or after stripping, the number of BrdU-labeled LC was considerably increased. Furthermore, after i.p. injection of colchicine in the nude mouse, human epidermal LC undergoing mitosis were evidenced by electron microscopy in the graft. Form these results we conclude that the LC are actively cycling–therewith a self-reproducing cell population in human epidermis