Topical retinoic acid inhibits changes in Langerhans cell density during carcinogenesis.

Ultraviolet radiation (UVR), chemical carcinogens and contact sensitisers all reduce the density of Langerhans cells (LC) in murine epidermis; UVR also lowers the number of Thy-1 dendritic epidermal cells (Thy-1+ dEC). Topical application of all-trans retinoic acid (RA) renders these cells insensitive to UVR and the tumour promoter 12-0-tetradecanoylphorbol 13-acetate (TPA) but does not inhibit LC migration from the epidermis in response to a contact sensitiser. Additionally, when the diet of mice was supplemented with the retinoid temarotene, UVR was unable to reduce the number of LC or Thy-1+ dEC. Hence one of the anti-carcinogenic mechanisms of retinoids may be to protect LC from carcinogens.