RSV immunoplaque assay
RSV titres were assessed by immunoplaque assay. Lung homogenates were titrated onto HEp-2 cell monolayers in 96-well plates. Twenty-four hours later monolayers were fixed and permeabilised with 2% H2O2 in methanol then bound with biotin-conjugate goat anti-RSV antibody (BioRad; Watford, Hertfordshire, UK). Plaques were visualised with extravadin peroxidase and AEC red (SigmaAldrich; Glasgow, Scotland, UK) and infection units observed by light microscopy.