Suppression of the cutaneous immune response following topical application of the prostaglandin PGE2.

UVB irradiation (290-320 nm) and topical applications of arachidonic acid (AA) in mice decrease the number of identifiable Langerhans cells and alter the cutaneous immune response. Application of contact allergens such as dinitrofluorobenzene (DNFB) to irradiated or AA-treated skin induces antigen-specific tolerance. Indomethacin (IM), a cyclooxygenase inhibitor, administered orally to mice prior to UVB irradiation or prior to the topical application of arachidonic acid, abrogates suppression of contact hypersensitivity (CHS) to DNFB. This suggests a byproduct of arachidonic acid generated through the cyclooxygenase pathway may be involved in the immune suppression. Topical application of various prostaglandins (PGE2, PGD2, PGF2 alpha, and CTXA2) did not cause alterations in the population density of the identifiable Ia+ dendritic Langerhans cells. PGE2, but no other tested agent, produced a suppression of the CHS response to DNFB. These observations suggests that of the various prostaglandins, PGE2 might be one of several biochemical signals which mediate the suppression of contact hypersensitivity reactions following ultraviolet radiation exposure. However, the mechanisms by which PGE2 produces its suppressive effects have not been identified.