NF-KAPPA-B ACTIVATION IS RESPONSIBLE FOR THE SYNERGISTIC EFFECT OF HERPES-SIMPLEX VIRUS TYPE-2 INFECTION ON INTERFERON-GAMMA-INDUCED NITRIC-OXIDE PRODUCTION IN MACROPHAGES

Nitric oxide (NO), produced in interferon (IFN)-gamma-activated murine macrophages by the enzyme inducible nitric oxide synthase (iNOS), has been found to have antiviral properties, We have previously shown tha t herpes simplex virus type 2 (HSV-2) infection of macrophages synergi stically enhances IFN-gamma-induced NO production, and we now extend t hese findings by providing evidence that virus-induced tumour necrosis factor (TNF)-alpha mediates activation of the transcription factor nu clear factor (NF)-kappa B, which in turn is responsible for the synerg istic effect, HSV-2 infection and IFN-gamma stimulation of macrophages synergistically induced TNF-alpha secretion and nuclear translocation of NF-kappa B, which bound to a sequence corresponding to a kappa B s ite in the iNOS promoter, The effect of HSV-2 on NF-kappa B and NO pro duction was eliminated when cells were treated with antibodies to TNF- alpha, and direct inhibition of NF-kappa B activation with pyrrolidine dithiocarbamate (PDTC) also blocked the effect of HSV-2 infection on N O production. The effect of the NF-kappa B activation inhibitor was no t mediated through inhibition of the production of interferon regulato ry factor (IRF)-1 or of TNF-alpha itself, and a possible alternative m echanism of activation of NF-kappa B through virus-induced activation of the kinase PKR was also ruled out, Thus, our data indicate that NF- kappa B activation, through virus-induced autocrine TNF-alpha secretio n, is responsible for the synergistic effect of HSV-2 infection on lFN -gamma-induced NO production, and that such activation might constitut e a mechanism by which high-output NO production is targeted to infect ious foci.