Effects of different biological response modifiers on interferon expression in bacterial lipopolysaccharide (LPS)-responsive and LPS-hyporesponsive mouse peritoneal macrophages

Abstract

We have previously shown that the antiviral state of explanted mouse peritoneal macrophages (PM) decays during in vitro culture and that this decay is much more rapid in Lpsd PM than it is in Lpsn PM. Moreover, Lpsn PM can transfer the antiviral state to other cells, whereas Lpsd PM cannot. In vitro treatment of Lpsn PM with different agents [i.e., bacterial lipopolysaccharide (LPS), interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha, macrophage colony-stimulating factor (M-CSF) and antibody to Mac-1 antigen] induced an antiviral state to vesicular stomatitis virus (VSV) which was inhibited by antibodies to IFN-beta. Treatment of Lpsn PM with LPS or IFN-gamma resulted in greater accumulation of IFN-beta mRNA, whereas no change in the barely detectable levels of IFN-alpha mRNA was observed. Marked accumulation of IFN-beta mRNA was also observed in PM after TNF-alpha treatment. M-CSF and IFN-gamma (but not LPS) also induced an IFN-mediated antiviral state in Lpsd PM. Low levels of spontaneous transcription of IFN-beta mRNA were detected in nuclei from Lpsd PM. Treatment of Lpsd PM with IFN-gamma for 3 h resulted in the accumulation of IFN-beta mRNA without any concomitant increase in the transcription of the IFN-beta gene, as determined by run-on transcription assays with isolated nuclei. The addition of as little as I international unit/ml of IFN-gamma to PM resulted in a 100-fold inhibition of VSV yield. As antibodies to IFN-alpha/beta inhibited only a portion of the IFN-gamma-induced antiviral state, such an antiviral state might reflect the synergism between IFN-gamma and endogenous IFN-beta. In fact, the addition of low doses of both IFN-gamma and IFN-beta to either Lpsn or Lpsd PM resulted in synergistic antiviral effects. In vivo treatment of Lpsd mice with granulocyte-macrophage (GM)-CSF, M-CSF, IFN-gamma or Newcastle disease virus rendered peritoneal cells capable of transferring an antiviral state. These results indicate that (i) various stimuli can induce IFN-beta production by PM, (ii) Lpsd PM spontaneously transcribe low levels of IFN-beta mRNA, even though they cannot transfer an antiviral state, (iii) different stimuli, but not LPS, induce a normal IFN response in Lpsd PM, (iv) IFN-gamma increases the accumulation of IFN-beta mRNA in Lpsd PM by post-transcriptional mechanisms and (v) IFN-gamma may act synergistically with endogenous IFN-beta in inducing a potent antiviral state to VSV in PM.