ULTRASTRUCTURAL CHANGES IN STRATUM-CORNEUM INDUCED BY ULTRAVIOLET LIGHT

[摘要] The ultrastructure of stratum corneum has been studied at intervals following a single ultraviolet exposure (4 times minimal erythema dose). A thick parakeratotic zone formed beneath the normal stratum corneum (distal corneal zone) at 72 hours post-irradiation. At 1 week after irradiation a 3rd layer (proximal corneal zone) formed beneath the parakeratotic layer and is comparable in thickness to the distal corneal zone, differing from it in only minor structural details. The rapid formation of this proximal corneal zone implies an accelerated epidermal renewal time. The parakeratotic zone possesses several distinct differences from normal stratum corneum. Not only are nuclei retained, but the normal lamellar organization of horny layer is replaced by large spheroidal and less well-defined cells which are believed to be incompletely keratinized. The keratin pattern of the parakeratotic zone is different from normal, unirradiated stratum corneum, and from distal and proximal corneal zones. Although keratin filament diameter appears normal (70 A) in the parakeratotic zone, the interfilamentous matrix is less dense than normal, implying that some alteration in synthesis of this matrix has been induced by ultraviolet light. Other alterations in parakeratotic postirradiated stratum corneum include the presence of peculiar oval lacunae (long axis 0.48 microns), well-preserved melanin granules, and groups of dense particles (130 A to 280 A diameter) thought to be ribosomes. A cell possessing a long dendrite-like process and melanin granules has been observed in parakeratotic stratum corneum and may be a melanocyte corpse.