Thymidine kinase and susceptibility to interferon are not involved in the increased virulence of recombinant viruses isolated following mixed ocular infection with HSV strains OD4 and CJ394.

We previously described the isolation of herpes simplex virus type 1 (HSV-1) intratypic recombinants that had increased ocular and neurovirulence. To better understand the mechanism of increased virulence, we have characterized two virulence-related factors, viral thymidine kinase (TK) activity and interferon (IFN) sensitivity, in the parental and recombinant viruses. The parental and recombinant viruses had comparable TK activities and were equally resistant to IFN-alpha, IFN-gamma and to a combination of the two IFNs. These results indicate that these factors are not involved in the increased virulence of the recombinant viruses.