FIG. 3.

Lung virus titers in the memory response to RSV challenge. (A) To determine the effect of treatment on lung virus titers in the memory response to RSV challenge, mice prophylactically treated with WT siRNA (WT), MM siRNA (MM), or PBS were challenged with 10⁶ PFU of RSV/A Long. The lungs were harvested at days 2, 4, and 6 postchallenge to determine virus titers as previously described (64). The data are presented as mean log₁₀ PFU/g titer ± the SE from n = 5 mice/treatment/time point in three separate experiments. (B) The lung histopathology was evaluated in the treated mice challenged with RSV. No lung histopathology was evident at day 0 prior to challenge for any treated group (data not shown). Histopathology was evaluated for WT siRNA-treated mice at day 2, 4, or 6 p.i. (panels i, iv, and vi, respectively); for PBS-treated mice at day 2, 4, or 6 p.i. (panels ii, v, and vii, respectively); and for MM siRNA-treated mice at day 2, 4, or 6 p.i. (panels iii, vi, and ix, respectively) as previously described (26). Asterisks indicate a significant (P < 0.01) difference from the control.