How Gut Bacteria Shape the Immune System and Affect Viral Illness
A study led by Dr. Caspar Ohnmacht from the Center of Allergy and Environment (ZAUM) and Prof. Dietmar Zehn from the Technical University of Munich has provided new insights into how gut bacteria – collectively known as the microbiome – shape the body’s immune response to viral infections. The research demonstrates that certain bacterial communities can boost the immune system’s ability to clear viruses, but this enhanced response may also intensify disease symptoms.
The Microbiome’s Impact on Immune Function
The study examined how a defined group of gut bacteria, known as OMM12, affects immune responses in mice infected with Lymphocytic Choriomeningitis Virus (LCMV) – a model virus used to study systemic infections.
The researchers discovered that mice colonized with OMM12 mounted a stronger immune response and cleared the virus more effectively from their intestines than other groups. However, this enhanced immunity came at a cost: the same mice also exhibited more severe symptoms highlighting a delicate balance between immune defense and disease severity.
A Complex Immune Response
Lead author Dr. Caspar Ohnmacht explained, “This research illustrates that while certain gut bacteria can support the immune system in fighting viruses, they may also intensify disease symptoms. It underscores the complex and sometimes double-edged relationship between the microbiome and human health.”
By using advanced cell analysis techniques, the team found that the OMM12 bacterial community activated T helper cells – key players in the immune response – triggering a strong antiviral reaction. Although this boosted the body’s ability to eliminate the virus, it also led to increased inflammation, ultimately worsening the overall disease outcome.
Implications for Future Treatments
The study highlights the significant influence of the microbiome on how the body responds to infections. It suggests that, in the future, therapies designed to modulate gut bacteria could enhance the effectiveness of treatments for viral infections, cancer, and even vaccines.
Dr. Ohnmacht noted, “The gut microbiome shows an enormous complexity and variability across individuals and is by itself shaped by the immune system. Our approach to reduce this complexity will help to identify specific metabolites that shape the immune response and will hopefully open new avenues for improving therapies by targeting the microbiome.”
By deepening our understanding of how gut bacteria shape immune responses, the research lays the foundation for future studies exploring microbiome-based strategies to prevent and treat a wide range of diseases.
Original Publication
Kolland et al., 2025: A specific microbial consortium enhances Th1 immunity, improves LCMV viral clearance but aggravates LCMV disease pathology in mice. Nature Communications. DOI: 10.1038/s41467-025-59073-x
