Decreased bacterial clearance from the lungs of mice following primary respiratory syncytial virus infection

Virus respiratory infections often precede bacterial pneumonia in healthy individuals. In order to determine the potential role of respiratory syncytial virus (RSV) in bacterial secondary infections, a mouse sequential pulmonary infection model was developed. Mice were exposed to RSV then challenged with Streptococcus pneumoniae (StPn). Exposure of BALB/c mice to 10(6)-10(7) plaque forming units (pfu) of virus of RSV significantly decreased StPn clearance 1-7 days following RSV exposure, This finding was not restricted to StPn alone: exposure to RSV followed by Staphylococcus aureus (SA) or Pseudomonas aeruginosa(PA) resulted in similar decreases in bacterial clearance. Both bronchoalveolar lavage (BAL) cell counts and pulmonary histopathology demonstrated that RSV-StPn exposed mice had increased lung cellular inflammation compared to mice receiving StPn or RSV alone. The effect of RSV infection on bacterial clearance was dependent on the mouse genetic background: C57BL/6J mice (relatively resistant to RSV infection) demonstrated a modest change in StPn clearance following RSV exposure, whereas FVBN/J mice (similar to the BALB/cJ mice in RSV susceptibility) demonstrated a similar degree of RSV-associated decrease in StPn clearance 7 days following RSV exposure. Neutrophils from the RSV-StPn sequentially exposed BALB/cJ mice were functionally altered-produced greater levels of peroxide production but less myeloperoxidase (MPO) compared to mice receiving StPn alone. These data demonstrate that RSV infection decreases bacterial clearance, potentially predisposing to secondary bacterial pneumonia despite increased lung cellular inflammation, and suggest that functional changes occur in the recruited neutrophils that may contribute to the decreased bacterial clearance.