Epidermal proliferation and keratinization following standardized elicitation with diphenylcyclopropenone.

Diphenylcyclopropenone (DCP) was applied to the upper arms of five alopecia areata patients using 10% of the concentration that had been applied previously to the scalp during topical immunotherapy. DCP applied in this concentration evoked a mild eczematous reaction. Biopsies were taken before DCP application and after 24, 48 and 96 h. A large increase in T-lymphocytes and CD14-positive cells in the dermis was seen after 24 h. Migration of these cells into the epidermis was mainly observed during the first 48 h. This was followed by epidermal proliferation as assessed by the number of Ki-67-positive nuclei and the degree of Ks8.12-binding. Both showed their main increase after 48 h; but after 24 h the increase of Ki-67-positive nuclei was significant (P < 0.04). Involucrin and filaggrin showed a gradual increase which became substantial after 96 h (both P < 0.04). As the invasion of inflammatory cells into the epidermis preceded the main increase in epidermal proliferation, cytokines are suggested as possible mediators for the initial phase of the proliferative response after DCP application.