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

Abstract

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.