TOPICAL TRETINOIN REPLENISHES CD1A-POSITIVE EPIDERMAL LANGERHANS CELLS IN CHRONICALLY PHOTODAMAGED HUMAN SKIN

Excessive exposure to sunlight results in drastic degradative changes in the constitutive cells of the epidermis. Among these is a profound abrogation of Langerhans cell number and function, leading to compromi sed immunologic competency. Retinoids have recently been shown to rest ore immunologic function in the setting of iatrogenic immunosuppressio n. We asked whether topical tretinoin would reverse Langerhans cell de pletion in chronically photodamaged skin. We examined the skin of 8 vo lunteers immunohistochemically before and after 6 months of daily appl ications of tretinoin. At baseline, there was a profound depletion of CD1a-positive Langerhans cells in the interfollicular epidermis, but n ot in the adjoining follicular epithelium. After tretinoin, all patien ts demonstrated replenishment of interfollicular epidermis by CD1a-pos itive Langerhans cells. This was associated with induction of HLA-DR e xpression on infundibular keratinocytes, as well as the appearance of CD1a dendritic cells in the papillary dermis. Thus, the enhancement of epidermal immunity in photodamaged skin may reflect restoration of an tigen-presenting Langerhans cells. The source of this renewed dendriti c cell population is likely to be follicular infundibulum and the papi llary dermis.