SUMMARYStimulation of mouse macrophages with Newcastle disease virus (NDV) leads to a rapid and high interferon (IFN) response. The magnitude of this response is influenced by the mouse genotype. We have analysed NDV-induced IFN production at the protein and mRNA levels in two different populations of macrophages derived from 'high producer' C57BL/6 and 'low producer' BALB/c mice in vitro. The data indicate that bone marrow and peritoneal macrophages from both strains grown in the presence of L cell conditioned medium (CM) as a source of macrophage colony-stimulating factor 1 (M-CSF) or purified murine M-CSF produce 10-to 50-fold more IFN on a per cell basis than cultures of resident peritoneal macrophages. These differences were also found when steady state levels of IFN mRNA were analysed. Differential analysis for the ratios of IFN-c~ and IFN-/~ showed that CM-or M-CSF-cultured macrophages produced equal amounts of both IFN species as determined by specific monoclonal antibodies and hybridization experiments using IFN-~ and IFN-/~ DNA probes, whereas resident peritoneal macrophages induced under identical conditions produced Mmost exclusively IFN-/L This suggests a stimulating effect of M-CSF on IFN synthesis in NDV-induced cultures of mouse macrophages, which is in part due to additional activation of IFN-c~ gene expression.

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