Segmented filamentous bacteria in the gut protect against secondary bacterial infections in the lung – Immunology Research

Respiratory viruses can substantially weaken immune responses and enhance the risk of secondary bacterial infections. These can be fatal — for example, during the 1918 influenza pandemic, bacterial pneumonia was the main cause of mortality. Susceptibility to secondary infections is partially due to a depletion of alveolar macrophages (AMs), which is a common feature of viral respiratory infections. In 2024, Gewirtz and colleagues showed that segmented filamentous bacteria (SFB) in the gut can protect AMs against virus-induced depletion and enhance their antiviral function. Now, the same group has found that SFB epigenetically and metabolically reprogram AMs, which provides protection against virus-induced depletion and also enhances their antibacterial function.

This applied across all age ranges (in humans, susceptibility to secondary infections increases with age), and protection started in infancy, with mothers transferring SFB to their offspring, probably via coprophagy.