An ex vivo study of congenital pigmented nevi in epidermal reconstructs

In order to study morphologic and functional characteristics of pigment cells in congenital pigmented nevi, autologous or heterologous reconstructs have been made using normal keratinocytes and nevus cells from the dermal-epidermal junction or from the dermis. All these cells, keratinocytes and nevus cells, were used as cell suspensions immediately after dissociation from the tissues or after subsequent brief cultivation in a serum-free medium. Reconstructed epidermis were cultured for 15 days at the air-liquid interface with or without ultraviolet (UV) B exposure. The reconstructs were examined macroscopically (formation of hyperpigmented macules), histologically (pigment cell nesting) and ultrastructurally (pigment structure and transfer). Typical nesting of nevus cells was observed in the dermal-epidermal junction or in the superficial dermis associated with macroscopically detectable small pigmented macules. UVB exposure induced an upward migration of nevus cells in the suprabasal layers of the epidermis. This tissue model can be considered as an excellent system for the ex vivo reproduction of pigmented nevi and as an assay of the sensitivity of nevus cells towards UVB irradiation.