TRIGGERING OF PERITONEAL-MACROPHAGES WITH IFN-ALPHA BETA ATTENUATES THE EXPRESSION OF INDUCIBLE NITRIC-OXIDE SYNTHASE THROUGH A DECREASE INNF-KAPPA-B ACTIVATION/

Triggering peritoneal macrophages with IFN-gamma and a low concentrati on of LPS induced the expression of the inducible form of nitric oxide synthase (iNOS). This process was significantly inhibited When IFN-al pha/beta was added during the initial 2 h after the start of IFN-gamma /LPS activation, Evaluation of the transcriptional activity using run- on assays indicated that IFN-alpha/beta inhibited the transcription of iNOS. Transfection experiments using a 1.7-kb promoter sequence corre sponding to the 5' flanking region of the murine iNOS gene showed decr eased promoter activity in the presence of type I IFNs, Analysis of th e transcription factors that participate in iNOS expression revealed a marked decrease of NF-kappa B activation, a nuclear factor required f or the transcription of this gene, The degradation of I kappa B alpha and I kappa B beta which is required for the translocation of NF-kappa B to the nucleus, was inhibited in the presence of IFN-alpha/beta. Ho wever, the activity of other transcription factors such as IFN regulat ory factor 1, which is involved in the expression of iNOS in response to IFN-gamma, was not affected by IFN-alpha/beta stimulation, These re sults suggest that in the presence of IFN-alpha/beta, the activity of the iNOS promoter is impaired, and this attenuated nitric oxide syntha se expression could be important in pathophysiologic situations in whi ch secretion of type I IFNs occurs.