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Interferon induction by viruses. XI. Early events in the induction process
Journal of Interferon Research
|January 1, 1984
Summary
Researchers used NH4Cl to study how Newcastle disease virus (NDV), Sindbis virus, and vesicular stomatitis virus (VSV) enter aged cells to induce interferon (IFN). They found distinct entry mechanisms, with Sindbis and VSV entry dependent on acidic conditions for RNA release into the cytosol.
Area of Science:
- Virology
- Cell Biology
- Immunology
Background:
- Understanding virus entry mechanisms is crucial for controlling viral infections and modulating immune responses.
- Interferon (IFN) induction is a key antiviral defense pathway initiated by the detection of viral components.
- Previous studies suggested that low pH-dependent fusion is involved in the entry of some viruses into cells.
Purpose of the Study:
- To elucidate the entry mechanisms of Newcastle disease virus (NDV), Sindbis virus, and vesicular stomatitis virus (VSV) into aged primary chick embryo cells.
- To investigate the role of low pH-dependent processes in viral entry and subsequent IFN induction.
- To differentiate the entry pathways of Sindbis virus and VSV using specific inhibitors.
Main Methods:
- Utilized NH4Cl, a lysosomotropic weak base, to disrupt low pH-dependent membrane fusion during virus entry.
- Monitored three key parameters: dose-response curves for IFN yield, activity of IFN-inducing particles (IFP), and quantum yield of IFN.
- Employed cytochalasin B to further distinguish between the entry mechanisms of Sindbis virus and VSV.
Main Results:
- NDV entry and IFN induction were unaffected by NH4Cl, indicating an acidic-independent fusion mechanism at the plasma membrane.
- Sindbis virus infectivity and IFP activity were inhibited by NH4Cl in a dose-dependent manner, consistent with acidic-fusion entry.
- VSV infectivity was highly sensitive to NH4Cl, while IFP activity remained largely functional, but IFN quantum yield was reduced, suggesting acidic-endocytosis and a critical step of RNA transfer from endosomes.
Conclusions:
- NDV, Sindbis virus, and VSV exhibit distinct entry mechanisms into aged chick embryo cells, influencing IFN induction.
- Sindbis virus and VSV share a common, rate-limiting step involving the transfer of viral RNA from acidic vacuoles to the cytosol.
- The study differentiates Sindbis virus (acidic-fusion) and VSV (acidic-endocytosis) entry pathways, highlighting the importance of endosomal pH for viral RNA release and subsequent IFN stimulation.