FIG 8.
Replication of rgRSV mutants in cotton rats. (A and B) RSV titer in lungs (A) and in nasal turbinates (B). Four-week-old SPF cotton rats were inoculated intranasally with 2.0 × 105 TCID50 of each rgRSV. At day 4 postinfection, the cotton rats were sacrificed, and lungs and nasal turbinates were collected for virus titration by TCID50 assay. The viral titers shown are the geometric mean titer (GMT) from 5 animals ± standard deviation. The detection limit is 2.0 log TCID50/g tissue. (C and D) RSV genome RNA copies in lungs (C) and in nasal turbinates (D). Total RNA was extracted from the homogenized tissue using TRIzol reagent. RSV genome copies were quantified by real-time RT-PCR. (E) Representative histologic changes from each group are shown. Hematoxylin-eosin (H&E) staining of lung tissue is shown. Histological images were taken under light microscopy. Micrographs with ×20 magnification (scale bar of 500 μm) are shown. (F) Histology score. Each slide was scored based on severity of peribronchiolitis, perivasculitis, bronchiolitis, alveolitis, and interstitial pneumonia. Scores: 0, no lesion; 1, mild; 2, moderate; 3, severe. NS, no significant difference (P > 0.05); *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001.