Influenza-induced monocyte-derived alveolar macrophages confer prolonged antibacterial protection

Area of Science:

• Immunology
• Respiratory Medicine
• Microbiology

Background:

• Influenza's long-term impact on lung immunity remains poorly understood.
• Understanding post-infection immune dynamics is crucial for managing secondary bacterial infections.

Purpose of the Study:

• To investigate the long-term effects of influenza infection on lung immunity and host defense.
• To characterize the immune cells responsible for altered protection after influenza recovery.

Main Methods:

• Murine model of influenza infection followed by Streptococcus pneumoniae challenge.
• Flow cytometry and transcriptomic analysis to phenotype and functionally assess alveolar macrophages (AMs).
• Epigenetic profiling of AM subsets.

Main Results:

• One month post-influenza, mice exhibited enhanced protection against Streptococcus pneumoniae.
• This protection was mediated by a distinct population of monocyte-derived AMs producing increased interleukin-6.
• Influenza-induced AMs possessed unique functional, transcriptional, and epigenetic profiles compared to resident AMs.

Conclusions:

• Influenza infection alters lung immune cell composition, promoting a protective AM population.
• Monocyte-derived AMs contribute to prolonged, but transient, antibacterial defense.
• Transient respiratory infections continuously shape lung immunity through recruitment of new immune cells.