Plaque Assay for Virus Quantification

A 6-well plate with 6 × 10⁵ RD cells/well was prepared and incubated overnight at 37 °C in 5% CO₂. Prior to viral infection, the complete growth medium (DMEM supplemented with 10% FBS) was removed and approximately 1 mL serial 10-fold dilutions of virus inoculum was added to the cells for 1 h at room temperature with gentle shaking to allow for virus attachment. After 1 h incubation, the inoculum was removed and replaced with 2 mL of 1.2% w/v carboxylmethylcellulose. After 72 h incubation, the plaque medium was removed and the cells were fixed with 4% formaldehyde and stained with 0.5% crystal violet. The plaques were visible against a white background.