Decreased pulmonary clearance of S-pneumoniae following influenza A infection in mice

In children, the incidence of complicated pneumonias (including empyemas an d lung abscesses) associated with Streptococcus pneumonia infection has inc reased in recent years. Ire many cases, these complicated pneumonias follow ed flu-like illnesses. To determine mechanisms behind this association, a m urine model of sequential pulmonary infection has been developed. BALB/cJ m ice infected with influenza A had mild pulmonary inflammation that resolved within 5-7 days. Seven days following their initial 'treatment' (mock infe ction or influenza exposure), mice were challenged with 10(6) cfu of S. pne umoniae, and their lungs were harvested at intervals fur analysis. Lungs of influenza-exposed mice demonstrated greater colony counts 24 and 48 h foll owing S. pneumoniae exposure compared to control mice. In addition, neutrop hil numbers were significantly increased in the influenza/S. pneumoniae seq uentially-infected animals compared to S. pneumoniae infection alone (1.4 /- 0.6 x 10(6) vs. 0.06 +/- 0.07 x 10(6) cells, P < 0.05, 24 h). Influenza- exposed animals had greater levels of IL-1 beta and TNF-alpha in lung homog enates following S. pnemoniae inoculation. These data demonstrate that mice exposed to influenza have enhanced inflammatory responses and increased ba cterial burden following S. pneumoniae exposure than do control mice. This model will be useful in defining mechanisms behind the enhanced susceptibil ity to S. pneumoniae that occurs after influenza exposure. (C) 2001 Elsevie r Science B.V. All rights reserved.