FIG. 5.

IFN-γ expression in the neonatal period protects against exacerbated weight loss. Four-day-old BALB/c mice were infected i.n. with 8 × 10⁴ FFU of RSV/wt, RSV/IFN-γ, or RSV/IL-4. The mice were challenged with 10⁶ FFU of wild-type RSV A2 i.n. at 8 weeks of age. (A) After challenge, weight was monitored daily and plotted against the starting weight. (B) On day 4 postchallenge, RNA was extracted from the lungs, and the amount of RSV L RNA was determined by real-time PCR. (C) Total RSV-specific Ig was measured in serum at day 7. (D and E) BAL fluid supernatants were taken on days 4 and 7 to determine the levels of IFN-γ (D) and IL-4 (E) by ELISA. Data are representative of two repeats, and points represent data for five mice per group ± SEM. **, P < 0.01; ***, P < 0.001.