Pawlowski A, Pawlowski MD, Lea PJ
DOI: 10.2340/0001555571113117

In order to investigate how sunlight may affect naevi and lentigines, their melanocytes and the basement membrane, three irradiation protocols were applied directly to ten naevi and five lentigines on 2 subjects. Neither volunteer had sufficient naevi and lentigines to be able to use the three irradiation protocols on each of the subjects. Skin biopsies were fixed in glutaraldehyde followed by osmium tetroxide, thin-sectioned and examined in a Hitachi H-7000 transmission electron microscope. Following 14 consecutive single exposures of 3 MED of UVB or single exposures followed by 25 J/cm2 of UVA, 350 J/cm2 UVA with either 2040 or 2280 mJ/cm2 UVB, the basement membrane maintained its continuity. Melanocytes were not observed on the dermal side of the epidermal-dermal junction. UVA irradiation stimulated reinforcement of the basement membrane zone by collagen fibers. Centrioles found in melanocytes following irradiation suggest that these melanocytes maybe undergoing mitosis. Dermal fibroblasts were found to contain comparatively large quantities of melanin pigment. The pigment contained in these fibroblasts may in fact constitute an additional barrier against UV irradiation.