THE UV ACTION SPECTRA FOR THE CLONE-FORMING ABILITY OF CULTURED HUMANMELANOCYTES AND KERATINOCYTES

Melanocytes (skin type 2) and keratinocytes were irradiated with UV li ght of 254, 297, 302, 312 and 365 nm and the survival was measured. Cl one-forming ability was chosen as the parameter for cell survival. Mel anocytes were found to be less sensitive to UV light than keratinocyte s (a difference of a factor 1.22-1.92 for the UV-C and UV-B wavelength s (254, 297, 301 and 312 nm) and a factor 6.71 for the UV-A wavelength (365 nm). Because melanin does not appear to protect against the indu ction of pyrimidine dimers the difference between melanocytes and kera tinocytes in the UV-C and UV-B region could not be explained by the pr esence of melanin in the melanocytes. The relatively small difference can be explained by the longer cell cycle of melanocytes, which provid es more time for the melanocytes to repair UV damage. In the UV-A regi on the difference between melanocytes and keratinocytes was much large r, suggesting that besides the longer cell cycle some additional facto rs must be involved in protection against UV-A light.