LOCALIZATION OF DNA-DAMAGE AND ITS ROLE IN ALTERED ANTIGEN-PRESENTINGCELL-FUNCTION IN ULTRAVIOLET-IRRADIATED MICE

Prior ultraviolet (UV) irradiation of the site of application of hapte n on murine skin reduces contact sensitization, impairs the ability of dendritic cells in the draining lymph nodes (DLN) to present antigen, and leads to development of hapten-specific suppressor T lymphocytes. We tested the hypothesis that UV-induced DNA damage plays a role in t he impaired antigen-presenting activity of DLN cells. First, we assess ed the location and persistence of cells containing DNA damage. A mono clonal antibody specific for cyclobutyl pyrimidine dimers (CPD) was us ed to identify UV-damaged cells in the skin and DLN of C3H mice expose d to UV radiation. Cells containing CPD were present in the epidermis, dermis, and DLN and persisted, particularly in the dermis, for at lea st 4 d after UV irradiation. When fluorescein isothiocyanate (FITC) wa s applied to UV-exposed skin, the DLN contained cells that were Ia(+), FITC+, and CPD+; such cells from mice sensitized 3 d after UV irradia tion exhibited reduced antigen-presenting function in vivo. We then as sessed the role of DNA damage in UV-induced modulation of antigen-pres enting cell (APC) function by using a novel method of increasing DNA r epair in mouse skin in vivo. Liposomes containing T4 endonuclease V (T 4N5) were applied to the site of UV exposure immediately after irradia tion. This treatment prevented the impairment in APC function and redu ced the number of CPD+ cells in the DLN UV-irradiated mice. Treatment of unirradiated skin with T4N5 in liposomes or treatment of UV-irradia ted skin with liposomes containing heat-inactivated T4N5 did not resto re immune function. These studies demonstrate that cutaneous immune ce lls sustain DNA damage in vivo that persists for several days, and tha t FITC sensitization causes the migration of these to the DLN, which e xhibits impaired APC function. Further, they support the hypothesis th at DNA damage is an essential initiator of one or more of the steps in volved in impaired APC function after UV irradiation.