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Langerhans cells are dendritic cells of the epidermis originating from bone marrow precursors which may exceptionally undergo mitosis within the skin. We report herein an electron-microscopic observation of a dividing LC within a seemingly hyperproliferative human epidermis. This observation further underlines the self-reproducing capacity of LC in situ and suggests that LC may respond to the same mitogenic stimuli as keratinocytes.

The assessment of cell proliferation is important to our understanding of hyperproliferative disorders. In this work we evaluated the proliferation characteristics of epidermal keratinocytes in diseases with abnormal keratinization by two different methods (immunostaining for the proliferating cell nuclear antigen//PCNA and histochemical staining for nucleolar organizer region//associated argyrophilic proteins//AgNORs). Twenty/seven specimens from diseases with an abnormal keratinization were studied and compared with specimens of normal human skin. As compared with the latter, the numbers of PCNA/positive epidermal keratinocytes were increased in psoriasis, congenital non/bullous ichthyosiform erythroderma, epidermolytic hyperkeratosis and chronic dermatitis and decreased in ichthyosis vulgaris, X/linked ichthyosis and pityriasis rubra pilaris. In most cases a parallel modification of AgNORs was found. We conclude that although PCNA immunolabelling and AgNOR staining do not provide strictly correlated values, both appear as useful markers for the assessment of keratinocyte proliferation in epidermal disorders.