Relationship between epidermal Langerhans cell density ATPase activity and the induction of contact hypersensitivity

Langerhans cells have been implicated as playing a crucial role as antigen-processing cells in the induction of positive immune responses to antigens presented through the skin. We have investigated the effects of carcinogenic doses of UVB-irradiation, psoralen plus UVA light (PUVA), PABA containing sunscreen preparations, and topically applied corticosteroids on both Langerhans cell densities and immunologic responsiveness to contact sensitizers applied to the treated site. The data presented demonstrate that UV-irradiation of skin or topical application of corticosteroids can create a local milieu in which DNFB cannot function as an effective stimulator of contact hypersensitivity. Further, we have shown that the effect induced by UV light is reversible, does not appear to be related to the numerous tissue destructive effects of UVB-irradiation, and that the correlation with the density of ATPase-positive cells is not absolute.