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A comparative study of entry modes into C6/36 cells by Semliki Forest and Japanese encephalitis viruses
T Hase1, P L Summers, W H Cohen
1Department of Ultrastructural Pathology, Walter Reed Army Institute of Research, Washington, D.C.
Abstract:
The entry modes of Semliki Forest virus and Japanese encephalitis virus into C6/36 cells were compared by electron microscopic observation. At physiological pH, the two viruses showed characteristically different entry modes. Following attachment to the plasma membrane, many SF virions appeared within plasma membrane invaginations and cytoplasmic vesicles; on the other hand, JE virions remained to be found exclusively at the cell surface, with no virions appearing within cytoplasmic vesicles. Electron microscopic observation, therefore, indicated that SF virus entered C6/36 cells by receptor-mediated endocytosis, while JE virus penetrated the cells at the surface and disintegrated at or near the adsorption sites. At pH 5.8, SF virus also entered C6/36 cells by direct penetration at the cell surface. On the basis of the present and other findings, the following working hypotheses are presented for future investigations: (a) at physiological pH, the fusion protein of SF virus is in an inactive state and needs to be activated by acidic pH within the endosome in order to act on the host-cell membrane, but that of JE virus is in an active state and is capable of dissolving the host plasma membrane at the cell surface immediately after the attachment; (b) the states of viral fusion proteins (inactive or active) at the time of viral attachment to the cell surface determine which of the two entry modes these viruses follow.
Insights
Semliki Forest virus enters cells via endocytosis, while Japanese encephalitis virus penetrates the cell surface. Viral fusion protein states at attachment dictate these distinct entry mechanisms.
Area of Science:
- Virology
- Cell Biology
- Microscopy
Background:
- Semliki Forest virus (SFV) and Japanese encephalitis virus (JEV) are significant human pathogens.
- Understanding viral entry mechanisms is crucial for developing antiviral strategies.
Purpose of the Study:
- To compare the entry modes of SFV and JEV into C6/36 cells.
- To investigate the role of pH and viral fusion proteins in viral entry.
Main Methods:
- Electron microscopic observation of C6/36 cells infected with SFV and JEV.
- Comparison of viral entry at physiological pH and pH 5.8.
Main Results:
- At physiological pH, SFV entered via receptor-mediated endocytosis, while JEV entered via direct surface penetration.
- At pH 5.8, SFV also utilized direct surface penetration.
- JEV virions disintegrated at the cell surface, whereas SFV virions were found within cytoplasmic vesicles.
Conclusions:
- Viral entry modes are distinct for SFV and JEV, influenced by pH.
- The state of viral fusion proteins (active or inactive) at attachment likely determines the entry pathway.