What is already known
Asthma — a long-term inflammatory disease of the lungs — affects about 300 million people worldwide. Previous research suggests that the gut microbiota can influence asthma and other inflammatory diseases. However, the exact microbial species and mechanisms involved remain unclear.
What this research adds
Working in mice, researchers found that the gut protozoan Tritrichomonas musculis affects lung immunity by creating a gut-lung connection. T. musculis activates immune cells in the gut that then move to the lungs, increasing the production of molecules that worsen asthma symptoms. However, this immune response also helps protect against infection with Mycobacterium tuberculosis, the bacterium responsible for tuberculosis.
Conclusions
The findings suggest that while T. musculis can worsen asthma, it might also help the body fight off infections, offering potential for new treatments targeting the immune system.
Asthma — a long-term inflammatory disease of the lungs — affects about 300 million people worldwide. A study done in mice now shows that a specific gut protozoan, called Tritrichomonas musculis, activates immune responses in the gut that indirectly affect the lungs, exacerbating asthma symptoms while also providing protection against infections such as tuberculosis.
The findings, published in Cell, suggest that while T. musculis can worsen asthma, it might also help the body fight off harmful microbes, offering potential for new treatments targeting the immune system.
Previous studies have shown that the gut microbiota can influence asthma and other inflammatory diseases. However, the exact microbial species and mechanisms involved remain unclear.
Kyle Burrows at the University of Toronto in Canada and his colleagues studied mice that had been colonized with T. musculis to examine its effects on immune responses in the lungs.
Fighting off infection
Colonization with T. musculis triggered immune responses that began in the gut but affected also the lungs. Central to this process were a type of immune cells that normally reside in the gut. In the presence of T. musculis, these cells migrated to the lungs, where they stimulated the activation of immune cells linked to allergic inflammation as well as the production of inflammatory molecules.
The increase in inflammatory molecules worsened asthma symptoms in mice, triggering airway inflammation and making breathing more difficult. However, this immune response also offered protection against infection with Mycobacterium tuberculosis, the bacterium responsible for tuberculosis.
The results suggest that T. musculis promotes long-lasting immune changes, creating what researchers call a “gut-lung immune axis.”
Personalized treatments
Next, the team looked at the fluid produced in the lungs and airways of people with severe asthma. There, they found traces of protozoan DNA, including species related to T. musculis. While the exact role of these microorganisms in people with asthma remains unclear, the findings points to a potential link between colonization with T. musculis and a subset of asthma cases, the researchers say.
Targeting immune pathways activated by T. musculis could thus pave the way for personalized treatments for respiratory diseases, for example therapies to manage airway inflammation or to boost immunity against tuberculosis, the authors say.
“These findings demonstrate that a commensal protozoan tunes pulmonary immunity via a gut-operated lung immune network, promoting both beneficial and detrimental disease outcomes in response to environmental airway allergens and pulmonary infections.”
