Abstract
We have investigated the steady-state turnover of murine epidermal Langerhans cells (LCs) using an X-irradiation model, 3H-thymidine autoradiography and cultured epidermal sheet explants, and by assessing the LC population in normal mice. The LC density after whole-body irradiation without any cutaneous shielding was not significantly different from that in skin shielded during whole-body irradiation (P > 0.05), indicating that the additional irradiation to the skin did not contribute to a decrease in LC density. In both instances, the LC number gradually decreased in a linear fashion. The results indicate that epidermal LCs continuously leave the epidermis and are continually replaced by circulating precursor cells from the bone marrow at a steady rate. Autoradiographic studies after a pulse injection of 3H-thymidine showed a labelling index of 0.013%, indicating that local mitosis is not an important contributor to the maintenance of the epidermal LC population. Although local X-irradiation resulted in temporary reduction of LC density, epidermal sheet explant culture obtained immediately after local X-irradiation showed no difference in LC density as compared with control unirradiated skin, indicating that the decrease in LC density was not due to significant LC destruction. From these data, we calculated that the half-life of murine LCs in the epidermis is approximately 9 days.
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