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Electron microscope observations on the entry of avian infectious bronchitis virus into susceptible cells
Abstract:
Infectious bronchitis virus was observed to enter cells of chicken chorioallantoic membrane by viropexis. There was no support for the suggestion that entry took place by fusion of viral and plasma membranes. The results of electron microscopy showed that virus attachment occurred both at 4 degrees and at 37 degrees C. Viropexis was not observed until the preparations were warmed. Similar results were obtained using chicken kidney cells. Quantitative data obtained from a plaque counting system employing chicken kidney cells indicated that attachment was the same at both temperatures and that some virus particles were taken up at 4 degrees C. Virus uptake was triggered by attachment of the virus to the cell membrane and the subsequent process of virus entry visualised by E. M. appeared to proceed without the involvement of lysosomal enzymes. No intracellular virus was located by electron microscopy in warmed preparations when virus was treated with specific antiserum, either before or after adsorption to the cells.
Insights
Infectious bronchitis virus enters chicken cells via viropexis, not membrane fusion. This viral entry mechanism is temperature-dependent, occurring upon warming after initial attachment.
Area of Science:
- Virology
- Cell Biology
- Immunology
Background:
- Infectious bronchitis virus (IBV) is a significant pathogen in poultry.
- Understanding viral entry mechanisms is crucial for developing effective control strategies.
- Previous hypotheses suggested viral-host cell membrane fusion as an entry route for IBV.
Purpose of the Study:
- To investigate the cellular entry mechanism of infectious bronchitis virus in chicken cells.
- To determine the role of temperature in viral attachment and uptake.
- To elucidate the pathway of IBV entry into host cells.
Main Methods:
- Electron microscopy was used to visualize virus-cell interactions.
- Chicken chorioallantoic membrane and kidney cells were utilized as model systems.
- A plaque counting system quantified viral uptake at different temperatures.
Main Results:
- IBV entry into chicken cells occurs via viropexis (endocytosis), not membrane fusion.
- Virus attachment was observed at both 4°C and 37°C, but viropexis required warming.
- Quantitative data confirmed attachment at both temperatures, with some uptake at 4°C, and entry proceeded without lysosomal enzymes.
Conclusions:
- Infectious bronchitis virus enters chicken cells through viropexis.
- Viral entry is triggered by attachment and subsequent temperature-dependent endocytosis.
- The findings exclude membrane fusion and lysosomal involvement in the early stages of IBV cell entry.
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