OPN expression is a marker of high RSV loads <i>in vivo</i>.

<p>(A) C57BL/6 mice were mock-infected or infected with 1 or 3 x 10⁶ RSV-L19F. (B) C57BL/6 mice were mock-infected or infected with 3 x 10⁶ RSV-L19F or rgRSV-A2. (A-B) Lungs were collected 3 dpi for protein isolation and levels of OPN in lung homogenates were determined by ELISA. Lung homogenates were obtained from individual mice and not pooled (n>4 per group). * p < 0.05, ** p < 0.01, **** p < 0.0001.