Immunohistochemistry for RSV antigen was performed on paraffin-embedded tissue as described previously (Meyerholz, et al., 2004 (link)). Briefly, sections were cut at 5μm thickness onto positively charged slides. Following routine deparaffinization, sections were treated with Pronase E (Protease Type XIV from Streptomyces griseus, Sigma) for 12 minutes at 37°C. Nonspecific binding was blocked by incubation in 20% normal swine serum. The sections were incubated with polyclonal goat anti-RSV antibody (BioDesign/Meridian) overnight at a concentration of 1:50 with 5% normal swine serum. The slides were rinsed and then incubated with biotinylated rabbit anti-goat secondary antibody (KPL) at a concentration of 1:300 in 5% normal sheep serum. A peroxidase block with 3% peroxide was followed by incubation with peroxidase-conjugated streptavidin (BioGenex) for 45 minutes. After two PBS washes, the color was developed with Nova Red. The slides were then counterstained with Harris' hematoxylin, dehydrated and cover-slipped.