Dose-dependent shift of apoptotic and unaltered melanocytes into the dermis after irradiation with UVA 1

Background: Intense UVA irradiation induces an increase in number, size and activity of intraepidermal melanocytes. The number of melanocytes and the activity of melanogenesis return to normal after cessation of irradiation. Objective: In this study, we aimed to clarify the mechanism of reduction of melanocytes by apoptosis to prevent an uncontrolled increase in melanocyte s within the epidermis, Methods: The position of the melanocytes before and after UVA 1 irradiation was controlled by electronmicroscopy and histochem istry using Fontana-Masson staining, The status of apoptosis was demonstrat ed immunohistologically by the use of p53 and bcl2, Results: A dose-depende nt shift of melanocytes into the cerium could be demonstrated, At low irrad iation doses (20 J/cm(2)) pendulous melanocytes protrude into the dermis wi thout losing contact to the dermoepidermal basement membrane. Higher irradi ation doses (60 J/cm(2)) lead to a total elimination of fibrillary degenera ted, apoptotic or even morphologically intact melanocytes into the cerium, Once transported into the cerium, the melanocytes can be detected there for more than 4 years, Conclusion: This shift mechanism seems to regulate and control UV-induced proliferation of epidermal melanocytes.