U.V. enhanced reactivation of U.V.-and gamma-irradiated adenovirus in normal human fibroblasts.

An enhanced reactivation (UVER) of U.V.-irradiated as well as of gamma-irradiated human adenovirus type 2 (Ad 2) was detected following infection of normal human fibroblasts which had been pre-irradiated with U.V. light. U.V.-irradiated or non-irradiated fibroblasts were infected with either non-irradiated or irradiated Ad 2, and at 48 hours after infection cells were examined for the presence of viral structural antigens (Vag) using immunofluorescent staining. Results obtained using 5 different normal fibroblast strains showed that irradiation of host monolayers with 10J/m2 immediately prior to infection gave a U.V. enhanced reactivation (UVER) factor +/- standard error equal to 3 . 1 +/- 1 . 2 for virus U.V.-irradiated with 1 . 2 x 10(3) J/m2, and 2 . 1 +/- 0 . 5 for virus gamma-irradiated with 2 x 10(4) Gy. For a fixed survival of about 5 . 9 x 10(-2) for irradiated virus, the efficiency of UVER for gamma-irradiated virus was about 0 . 18, slightly less than the value of about 0 . 24 obtained for U.V.-irradiated virus. The results of time course experiments indicated that while U.V.-irradiation of normal host monolayers prior to infection gave rise to an increased rate of Vag formation for infection by unirradiated Ad 2, U.V.-irradiation of the cells increased the proportion of cells able to repair U.V.-damaged virus as well as allowing an earlier onset and/or increased rate of synthesis of Vag from a U.V.-damaged template. Similar experiments involving gamma-ray enhanced reactivation (gamma-RER) of irradiated Ad 2 indicated that gamma-RER and UVER may operate, in part at least, by different mechanisms in normal human cells.