Novel activation of γ-interferon in nonimmune cells during human cytomegalovirus replication

This in the first study documenting the induction of γ-interferon (IFN- γ) in human embryonic fibroblasts during human cytomegalovirus (HCMV) replication. Infection of cells with HCMV resulted in the consistent production of IFN-γ RNA, as determined by RT-PCR and Northern blot analysis. Western blot analysis of cell lysates and immunoprecipitates from the cultural fluids of infected cells demonstrated the presence of IFN-γ at the protein level. Induction of IFN-γ required infectious HCMV, since high-dose ultraviolet inactivation of the virus stock eliminated IFN-γ production. Further, IFN-γ induction appears to be a late event in the virus replication cycle, since inhibition of HCMV DNA synthesis (e.g., phosphonoacetic acid) blocked the increase in IFN-γ. Soluble factor(s) released from HCMV-infected cells apparently did not contribute to the induction of IFN-γ, since virus stocks from which virus had been removed by sedimentation did not induce production of IFN-γ. The appearance of IFN-γ at late stages of HCMV infection and its elimination in the presence of an inhibitor (Actinomycin D) of RNA synthesis indicate a true transcriptional induction of this lymphokine at the RNA and protein levels. The significance of IFN-γ production with regard to the replication and pathogenesis of HCMV in vitro and in vivo will require further investigation.