FIG 4.

kDB1 attenuation and histopathology following challenge in cotton rats. Groups of 3 cotton rats were inoculated intranasally (i.n.) with either kRSV-A2 or kDB1. Lung lavage (A) and nasal wash (B) were performed on day 4 p.i., and viral titers were measured by plaque assay. To evaluate for vaccine-attributable enhanced disease postchallenge, groups of 5 cotton rats were inoculated i.n. with either a control or kDB1 or intramuscularly (i.m.) with FI-RSV. Animals vaccinated with FI-RSV also received a boost on day 21 p.i. All animals were challenged with kRSV-A2-line19F on day 46 p.i., lungs were harvested 6 days later, and histopathology scores were determined (C). Representative hemotoxylin and eosin stains for FI-RSV-vaccinated (D), mock-vaccinated (E), and kDB1-vaccinated (F) rats are shown. Data are presented as means + SDs. *, P < 0.05.