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Influenza virus infection and bacterial clearance in young adult and aged mice
P R Wyde1, H R Six, M W Ambrose
1Influenza Research Center, Baylor College of Medicine.
Abstract:
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.
Insights
Influenza A (H3N2) virus infection impairs bacterial lung clearance in mice. Aged mice show a more pronounced deficit in clearing Staphylococcus aureus or Serratia marcescens after infection.
Area of Science:
- Immunology
- Microbiology
- Gerontology
Background:
- Bacterial lung infections can be exacerbated by concurrent viral infections.
- Influenza A virus (H3N2) is a significant respiratory pathogen.
- Age-related changes can impact immune responses to infection.
Purpose of the Study:
- To investigate the impact of influenza A (H3N2) virus infection on the lung clearance of bacteria (Staphylococcus aureus and Serratia marcescens).
- To compare these effects in young adult and aged mice.
Main Methods:
- Mice of two age groups (young adult and aged) were infected with influenza A/Hong Kong/68 (H3N2) virus.
- Following viral infection, mice were challenged with Staphylococcus aureus or Serratia marcescens.
- Pulmonary bacterial clearance, viral titers, interferon levels, pulmonary histopathology, and immune cell activity were assessed.
Main Results:
- Virus-infected mice, both young and aged, demonstrated significantly reduced bacterial clearance compared to controls.
- Aged, virus-infected mice exhibited a more pronounced deficit in bacterial clearance.
- This enhanced deficit in aged mice did not correlate with viral load, interferon levels, or lung tissue damage.
- Phagocytic and bactericidal activities of lung immune cells (macrophages and neutrophils) were comparable between infected young and aged mice.
Conclusions:
- Influenza A (H3N2) virus infection compromises the lung's ability to clear bacteria in a manner that is exacerbated by age.
- Age-related susceptibility to secondary bacterial pneumonia following influenza may not be solely explained by viral load or immune cell function.