EXPRESSION OF INTERFERON-GAMMA BY A CORONAVIRUS DEFECTIVE-INTERFERINGRNA VECTOR AND ITS EFFECT ON VIRAL REPLICATION, SPREAD, AND PATHOGENICITY

A defective-interfering (DI) RNA of the murine coronavirus mouse hepat itis virus (MHV) was developed as a Vector for expressing interferon-g amma (IFN-gamma). The murine IFN-gamma gene was cloned into the DI vec tor under the control of an MHV transcriptional promoter and transfect ed into MHV-infected cells. IFN-gamma was secreted into culture medium as early as 6 hr posttransfection and reached a peak level (up to 180 U/ml) at 12 hr posttransfection. The DI-expressed IFN-gamma (DE-IFN-g amma) exhibited an antiviral activity comparable to that of recombinan t IFN-gamma and was blocked by a neutralizing monoclonal antibody agai nst IFN-gamma. Treatment of macrophages with DE-IFN-gamma selectively induced the expression of the cellular inducible nitric oxide synthase and the IFN-gamma-inducing factor (IGIF) but did not affect the amoun ts of the MI-iv receptor mRNA. Antiviral activity was detected only wh en cells were pretreated with IFN-gamma for 24 hr prior to infection; no inhibition of Virus replication was detected when cells were treate d with IFN-gamma during or after infection. Furthermore, addition of I FN-gamma together with Mi-iv did not prevent infection, but appeared t o prevent subsequent viral spread. MI-Iv Variants with different degre es of neurovirulence in mice had correspondingly different levels of s ensitivities to IFN-gamma treatment in vitro, with the most virulent s train being most resistant to IFN-gamma treatment. Infection of suscep tible mice with DE-IFN-gamma-containing virus caused significantly mil der disease, accompanied by more pronounced mononuclear cell infiltrat es into the CNS and less virus replication, than that caused by virus containing a control DI vector. This study thus demonstrates the feasi bility and usefulness of this MHV DI Vector for expressing cytokines a nd may provide a model for studying the role of cytokines in MHV patho genesis. (C) 1997 Academic Press.