Topical and oral retinoids protect Langerhans' cells and epidermal Thy-1+ dendritic cells from being depleted by ultraviolet radiation.

Murine epidermis contains two types of bone marrow-derived cells of the immune system, Langerhans' cells (LC), which are dendritic antigen-presenting cells, and Thy-1+ dendritic cells (Thy-1+ DEC), which express the gamma/delta T-cell receptor for antigen and hence are probably T cells whose function in the epidermis is unknown. Ultraviolet (UV) light greatly reduces the density of both of these cell types, and hence this may be one of the mechanisms by which UV light induces immunosuppression. It is important to develop strategies for protecting these cells from the effects of UV light. In this study we show that topical all-trans-retinoic acid (RA) and an orally administered retinoid, temarotene, protect both LC and Thy-1+ DEC from being depleted by UV light. However, neither retinoid inhibited the development of immunosuppression in response to application of a contact sensitizer. We also compared two congenic mouse strains, one albino, the other lightly pigmented and capable of tanning in response to UV light. There was no difference in the ability of UV light to deplete LC or Thy-1+ DEC in these two strains or of retinoids to inhibit their depletion. These studies demonstrate that retinoids but not melanin are able to inhibit UV light from depleting LC and Thy-1+ DEC; however, there are other immunosuppressive effects of UV light which are not protected by the retinoids.