Interferon-induced expression of If-1h and If-1l alleles in Newcastle disease virus-infected mouse macrophages is associated with specific differences in viral gene transcription

Human Neutrophils Produce Macrophage Inhibitory Protein-1β but Not Type I Interferons in Response to Viral Stimulation

Several cell types have been shown to produce type I interferons (IFN). Of human leukocytes, monocytes and especially type 2 dendritic cell precursors (pDC2) seem to be the main producers and also have a wide spectrum of cytokine production. However, neutrophils seem to have a limited capacity for cytokine production but possess efficient defense mechanisms vs. bacterial infection by phagocytosis and degranulation. To determine whether they also have antiviral functions, IFN-alpha and IFN-beta were measured in preparations of pure neutrophils. The capacity of neutrophils to produce type I IFN is controversial. Additionally, macrophage inflammatory protein-1alpha (MIP-1alpha) and MIP-1beta were measured, as they are described to have indirect or direct antiviral activity. As stimulants, active and inactivated Newcastle disease virus (NDV), Sendai virus, and granulocyte colony-stimulating factor (G-CSF) were used. Peripheral blood mononuclear cells (PBMC) from the same donors were highly reactive to viral stimulation, whereas neutrophils failed to produce IFN but produced MIP-1beta in response to NDV. We conclude that neutrophils fail to prevent viral infection by IFN production but probably possess alternative mechanisms, such as secreting MIP-1beta in response to viruses.

Lipopolysaccharide inhibits virus-mediated induction of interferon genes by disruption of nuclear transport of interferon regulatory factors 3 and 7

We have studied the effects of lipopolysaccharide (LPS) on the Newcastle disease virus (NDV)-mediated induction of cytokine genes expression. Raw cells treated with LPS before or after virus infection showed down-regulation in the expression of interferon A and, to a lesser extent, interferon B genes. In contrast, induction of the interleukin (IL)-6 gene was enhanced. The effects of LPS were not a result of the suppression of virus replication, because the transcription of viral nucleocapsid gene was not affected. Consistent with these findings, LPS also suppressed the NDV-mediated induction of chloramphenicol acetyltransferase reporter gene driven by murine interferon A4 promoter in a transient transfection assay. Furthermore, LPS inhibited virus-mediated phosphorylation of interferon regulatory factor (IRF)-3 and the consequent translocation of IRF-3 from cytoplasm to nucleus. The LPS-mediated inhibition of IFNA gene expression was much weaker in infected Raw cells that constitutively overexpressed IRF-3. The nuclear translocation of IRF-7 in infected cells was also inhibited by LPS. These data suggest that LPS down-regulates the virus-mediated induction of IFNA genes by post-translationally targeting the IRF-3 and IRF-7 proteins.