A novel plaque assay system for paramyxoviruses

Area of Science:

• Virology
• Cell Biology
• Biochemistry

Background:

• Newcastle disease virus (NDV) and Sendai virus plaque assays are crucial for viral characterization.
• Standard plaque assay methods often require specific cell lines or serum-free conditions, limiting their application.
• Avirulent NDV strains typically do not form plaques under standard conditions.

Purpose of the Study:

• To develop an improved overlay medium for efficient plaque assay of NDV and Sendai virus.
• To enable plaque formation for previously non-plaque-forming avirulent NDV strains.
• To simplify viral plaque assay procedures by eliminating the need for specialized cell lines or serum-free media.

Main Methods:

• Supplementing normal overlay medium with 5% allantoic fluid, 200 µg/ml DEAE-dextran, and 30 mM MgCl2.
• Infecting secondary chick embryo fibroblasts with avirulent NDV strains and Sendai virus strain Z.
• Observing and quantifying plaque formation on treated and untreated cell monolayers.

Main Results:

• The modified overlay medium facilitated the formation of large, clear plaques for avirulent NDV strains that previously did not produce plaques.
• Plaque assay of Sendai virus strain Z was successfully achieved using this modified overlay.
• The method eliminated the requirement for specialized cell lines and serum-free medium.

Conclusions:

• A combination of allantoic fluid, DEAE-dextran, and MgCl2 in overlay medium significantly enhances plaque assay efficiency for certain viruses.
• This optimized plaque assay protocol offers a more accessible and versatile method for viral quantification and characterization.
• The findings provide a valuable tool for virology research, particularly for studying viruses that are difficult to assay using conventional methods.