Noninvasive molecular imaging of interferon beta activation in mouse liver

Interferon beta (IFN-β) is the priming cytokine in the interferons (IFNs) response that plays essential roles in innate immune system. Only very few studies on IFN activation in animals have been reported before, therefore, we embarked to develop a novel method to dynamically examine IFN-β activation in mouse liver by noninvasive molecular imaging.

Interferon beta promoter-directed firefly luciferase gene was integrated into chromosomes of hepatocytes by hydrodynamic injection. Mouse hepatitis virus type 3 (MHV-3) and polyinosinic-polycytidylic acid [poly(I:C)] were used to stimulate the activation of IFN-β. Luciferase activity was used as an indicator of the IFN-β promoter activity in vitro and in vivo. The expression level of IFN-β in the sera and firefly luciferase in the liver was assessed by ELISA and bioluminescence imaging respectively. Western blot was used for detecting proteins expression.

A rapid and elevated luciferase expression in the mouse liver induced by poly (I:C) and MHV-3 was detected by bioluminescence imaging. The detectable level of IFN-β in the sera was not induced by MHV-3. Moreover, IFN-β activation was significantly inhibited by the hepatitis C virus (HCV) NS3/4A protease in mouse liver. These results were consistent with IFN-β production in the sera. Therefore, a novel visual method to monitor IFN-β promoter activity was established in the current study.

This novel sensitive method can be used for not only assessing IFN-β activation or inhibition in the liver under different conditions, but also screening drug candidates of stimulating or inhibiting of IFN-β production.