ELECTRON-MICROSCOPIC OBSERVATIONS OF DYSKERATOSIS, APOPTOSIS, COLLOID BODIES AND FIBRILLAR DEGENERATION AFTER SKIN IRRITATION WITH DITHRANOL

Dying cells undergo coagulative necrosis or apoptosis. In the skin, apoptosis is known to occur in graft‐versus‐host reactions, in lichen planus, during regression of plane warts and neoplasms, and after physical injury caused by ultraviolet light resulting in sunburn cells. The present study shows that primary skin irritation also causes apoptosis. Mild, or moderate‐to‐con‐siderable, dithranol irritation of healthy uninvolved human skin caused focally coagulative necrosis of keratinocytes and also apoptosis of scattered keratinocytes, i.e. condensation of chromatin and cytosol, clumping of tonofilaments and budding of membrane‐bound cell fragments. These apoptotic cell fragments were engulfed in the epidermis by macrophages. Colloid bodies were detected in the upper dermis and apparently represented non‐phagocytosed apoptotic cell fragments that had dropped down from the epidermis. Dithranol also caused fibrillar degeneration of melanocytes and in some cases of Langerhans' cells, indicating that colloid bodies in the upper dermis could partly derive from these cell types. The significance of apoptosis in irritant contact dermatitis could be to maintain homeostasis of epidermis and counteract the hyperplastic response caused by irritant stimuli. Another possibility is that apoptosis was the response to an injury less severe than that causing necrosis. Copyright © 1990, Wiley Blackwell. All rights reserved