Distribution

The distribution of LCs in normal human skin is homogenous at a density of approximately 450/mm2 along the entire body; only the palms and soles show lower cell densities of approximately 60/mm2 (Berman et al. 1983). In normal human skin, LC frequency varies between 0.5% and 2.0% of all epidermal cells (Wollenberg and Bieber 2002).

The number of LCs is decreased in lesional skin of patients with LE compared with their nonlesional or perilesional skin, other inflammatory skin diseases, or normal skin (Bos et al. 1986, Shiohara et al. 1988, Sontheimer and Bergstresser 1982, Wollenberg et al. 2002). In another study, LCs were found to be reduced only in atrophic areas of the lesions (Mori et al. 1994). In perilesional epidermis, the numbers of CD1a+ and HLA-DR+ DCs are similar or identical to those in normal skin of healthy individuals (Mori et al. 1994).

Light sensitivity is an important clinical characteristic of LE, which is mirrored by immunohistochemical abnormalities after light irradiation. In the lesional epidermis of patients with light-induced LE and patients with polymorphous light eruption, the number of CD1a+ cells is diminished compared with that in nonirradiated skin (Velthuis et al. 1990). Although a relatively high number of DCs is found in the der-

mis of patients with polymorphous light eruption, only a small number of LCs is seen in light-induced LE lesions (Velthuis et al. 1990).

Other skin diseases with reduced LC numbers include chronic graft-vs-host disease, sarcoidosis, and acquired immunodeficiency syndrome (Aractingi et al. 1997, Belsito et al. 1984, Fox et al. 1983). In graft-vs-host disease, the reduced number of LCs may imply an attack by donor T cells (Suitters and Lampert 1983). The increase in CD1a-expressing epidermal DCs in inflammatory skin diseases such as atopic dermatitis and psoriasis, which has frequently been attributed to LC, is due to IDECs, a non-LC DC population (Wollenberg et al. 1999). Immunosuppressive treatment such as glucocorticosteroids or psoralen-UVA therapy may reduce LC numbers in the epidermis (Ashworth et al. 1989, Berman et al. 1983).

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