Microbes that live in our gut don’t just digest food. They also have far-reaching effects on the immune system. A new study shows that a particular gut microbe can prevent severe flu infections in mice, likely by breaking down naturally occurring compounds, called flavonoids, commonly found in foods such as black tea, red wine, blueberries and chocolate.
The microbiota is know to modulate the host response to influenza infection through as yet-unclear mechanisms
The study, conducted in mice by scientists at Washington University School of Medicine in St. Louis, also indicates that the strategy is effective in staving off severe damage from flu when the interaction occurs prior to infection with the influenza virus. This work also could help explain the wide variation in human responses to influenza infection.
Influenza infection, characterized by fever, cough and body aches, is a common and sometimes deadly viral infection of the upper respiratory tract. Older adults, pregnant women, young children and people with chronic health problems such as asthma and heart disease are most prone to serious complications. Around the world, the WHO estimates there are 250,000 to 500,000 flu-related deaths annually.
The researchers aimed to identify just what gut microbes might provide protection against severe influenza virus. For years, flavonoids have been thought to have protective properties that help regulate the immune system to fight infections.
The researchers used a mouse model and found that a microbially associated metabolite, desaminotyrosine (DAT), protects from influenza virus through augmentation of type I Interferon (IFN) signaling and diminution of lung immunopathology. A specific human-associated gut microbe, Clostridium orbiscindens, produced DAT and rescued antibiotic-treated influenza-infected mice. This metabolite protected the host by priming the amplification loop of type I IFN signaling.
Although the lungs of DAT-treated mice didn’t have as much flu damage, their levels of viral infection were identical to those in mice that didn’t get the treatment. Which means that the microbes and DAT didn’t prevent the infection itself, because the mice still had the virus. But the DAT kept the immune system from harming the lung tissue. A mechanism similar to what vaccines do.
With DAT, it may be possible to keep people from getting quite sick if they do become infected. The strategy used by the researchers doesn’t target the virus. Instead, it targets the immune response to the virus. Which could be valuable because there are challenges with therapies and vaccines that target the virus due to changes in the influenza virus that occur over type.
The researchers said that it might not be a bad idea to drink black tea and foods rich in flavonoids before the next flu season begins. Next steps for the researchers include identifying other gut microbes other than Clostridium orbiscindens, that can also use flavonoids to influence the immune system, as well as exploring ways to boost the levels of those bacteria in people who aren’t adequately colonized.
Washington University School of Medicine. “Natural compound coupled with specific gut microbes may prevent severe flu: Mouse study reveals how gut microbes fight influenza.” ScienceDaily. ScienceDaily, 3 August 2017.
Ashley L. Steed, George P. Christophi, Gerard E. Kaiko, Lulu Sun, Victoria M. Goodwin, Umang Jain, Ekaterina Esaulova, Maxim N. Artyomov, David J. Morales, Michael J. Holtzman, Adrianus C. M. Boon, Deborah J. Lenschow, Thaddeus S. Stappenbeck. The microbial metabolite desaminotyrosine protects from influenza through type I interferon. Science, 2017; 357