Influenza Virus Infection and Bacterial Clearance in Young Adult and Aged Mice

The effects of influenza A/Hong Kong/68 (H3N2) virus infection on clearance of bacteria (Staphylococcus aureus or Serratia marcescens) from lungs of young adult (8-week-old) and aged (2-year-old) CBA/2N mice were studied. No consistent differences in pulmonary bacterial clearance were observed in uninfected animals of either age group. However, both young and aged virus-infected mice consistently exhibited significantly reduced ability to clear challenge bacteria from their lungs compared to age-matched nonvirus-infected controls; this deficit was markedly more pronounced in virus-infected aged mice. The extra deficit seen in virus-infected aged animals did not correlate with pulmonary virus or interferon titers, or with severity of pulmonary histopathology. Moreover, the phagocytic and bactericidal activities of pulmonary macrophages and polymorphonuclear neutrophiles from virus-infected young and aged mice were comparable.