Influence of double infections on the induction of thymidine kinase by UV-irradiated herpes simplex virus types 1 and 2 and pseudorabies virus.

Simultaneous infection of primary rabbit kidney cells with HSV type 1 TK+ and a TK- strain results in a mutual influence of both viruses on the induction of thymidine kinase (TK). TK+ virus has an enhancing and TK- virus a depressing effect on TK induction by a superinfecting TK+ virus. The enzyme induction depends on the ratio of multiplicities of both viruses. The mutual influence on TK induction depends further on the time of addition of the superinfecting virus: the effect of the second virus can still be observed when given 6 hours after primary infection. Identical phenomena can be observed using combinations with HSV type 2 or Pseudorabies viruses. The ability of HSV to induce TK is progressively inactivated with increasing the time of UV-irradiation. The depressing effect of a TK- strain and the stimulating effect of a TK+ strain on superinfecting TK+ strains is UV-sensitive: after 6 minutes of UV-irradiation neither inhibition nor stimulation of TK induction by a superinfecting TK+ strain can be observed. Infection by long-term (20 minutes) UV-irradiated TK+ strains results in a depression of TK induction by a superinfecting TK+ virus. Long-term irradiation of the TK- virus does not show this effect. Cytosine-arabinoside has no effect on the mutual influence of TK induction by TK+ and TK-strains; the phenomenon of mutual depression therefore has to be considered an early process.