Distribution of CD1a-positive cells in psoriatic skin during the evolution of the lesions.

Normal skin and psoriatic lesions from 35 patients were investigated immunohistochemically with regard to the CD1a+ cell population (Langerhans' cells and indeterminate cells) in the epidermis as well as in the dermal infiltrate. In the normal-appearing skin, we found the regularly typical pattern of CD1a+ dendritic cells in suprabasal position, but in lesional skin of chronic psoriasis the CD1a+ cells were scattered in the acanthotic epidermis. In initial lesions, CD1a+ cells represent up to 50-60% of the infiltrating cells of the dermal compartment, in several cases being preferentially localized in the upper part of the papillar dermis close up to the epidermal CD1a+ cells in basal position, whereas in chronic psoriasis they represent less than 10%. These results suggest that in psoriasis vulgaris, CD1a+ cells actively migrate between the epidermis and the dermal vessels.