Keratinocyte apoptosis may be induced by ultraviolet-B radiation and represents a potential source of fragmented autoantigens in autoimmune diseases. This study investigates whether excessive keratinocyte apoptosis occurs in the skin lesions of cutaneous lupus (CLE) and dermatomyositis (DM) and the potential mechanisms responsible for this phenomenon. Skin biopsies have been studied from 19 patients with CLE and DM, eight with scleroderma, and five healthy controls. Apoptosis was detected by in situ end-labelling of fragmented DNA. The expression of Bcl-2, PCNA, p53, and Ki-67 proteins was studied by immunohistochemistry. In DM and CLE skin, the number of apoptotic keratinocytes was significantly increased (p=0.008) compared with normal skin. In both diseases, a large accumulation of apoptotic keratinocytes and apoptotic bodies was present in the disrupted basal zone. Unlike normal skin, a large number of keratinocytes, particularly those morphologically apoptotic, expressed p53 protein. A significant increase in the number of proliferating Ki-67 positive (p=0.0007) and PCNA-positive (p=0.0008) nuclei was also observed. In both CLE and DM, exaggerated and inappropriate keratinocyte apoptosis occurs. It is associated with increased expression of p53 and PCNA. This suggests that normal solar radiation alone or in combination with additional local factors induces DNA damage and excessive keratinocyte apoptosis in these autoimmune diseases of the skin. Apoptosis can mediate the severe epidermal lesions observed in both diseases and the release of fragmented autoantigens into the dermis.
Copyright 1999 John Wiley & Sons, Ltd.