EFFECTS OF REPEATED SUBERYTHEMAL DOSES OF UVA IN HUMAN SKIN

There is now evidence that UVA wavelengths (320-400 nm) in sunlight ma y contribute to the clinical changes commonly observed in photodamaged skin. We examined the effects of repetitive, suberythemal doses of UV A radiation on human skin in order to identify the epidermal and derma l changes indicative of early tissue injury. For these purpose, two ar eas of the back of fourteen female volunteers, phototype I to III, 20 to 40-year-old, were exposed three times a week for 13 weeks, to incre asing doses of UVA (330-440 nm) resulting in a cumulative dose of 1,20 0 J/cm(2). During the exposure period, biophysical and clinical change s were examined. After the last irradiation, a series of epidermal and dermal parameters were analyzed and quantified by histochemical stain ing in combination with image analysis on biopsied tissue sections. UV A induced a strong pigmentation with no alteration of microtopography. Skin hydration and elasticity decreased, whereas total skin thickness , assessed by echography, remained unchanged. Histologically, irradiat ed epidermis revealed an absence of hyperplasia, a significant thicken ing of the stratum corneum with an increased number of stratum corneum layers, a depletion of Langerhans cells and an increase in the expres sion of the protective protein, ferritin. No significant alteration wa s seen using antisera against type IV collagen or laminin, suggesting that the dermal-epidermal junction (DEJ) was largely preserved. In the dermis, enhanced expression of tenascin was seen below the DEJ, but t ype I procollagen localized at the same site was unaltered. Although w e were unable to visualize any change in elastic fiber content using L una staining, using an immunofluorescence technique we noticed an incr eased deposition of lysozyme on elastin fibers, confirming the results of Lavker. These findings suggest that chronic suberythemogenic doses of UVA, resulted in morphological and histological skin changes.