Only 43% of cells in our body are human. The rest are derived from a range of microorganisms in the gastrointestinal tract, such as bacteria, viruses, and fungi. These organisms, known as the gut microbiota, have evolved with humans to form a mutually beneficial relationship: we provide them with nutrients and a safe host environment, while the microbiota helps us process foods and derive energy. Furthermore, the microbiota plays a key role in human health: perturbations to the gut microbiota exacerbate autoimmune diseases and affect responsiveness to immunotherapy. However, the mechanisms through which the gut microbiota impacts human health remain poorly understood.

Researchers at Harvard Medical School have recently shed light on this mystery. Using a special type of mice whose cells glow when exposed to certain wavelengths of light, the researchers followed the migration of colon cells in mice with a healthy or depleted gut microbiota. They observed that in the former, immune cells migrated out of the colon and ended up at infection and tumor sites that had been experimentally induced. The migration to diseased areas was impaired when the gut microbiota was depleted by antibiotics or colitis, a gut inflammatory disease, resulting in a worse disease outcome compared to mice with a healthy microbiota.

This work shows for the first time that immune cells that reside in the colon have a key role in human health and that their function is dependent on a healthy gut microbiota. Given that microbial health is mostly determined by our diet, the study also proposes a potential mechanism through which lifestyle choices impact health. Hence, consuming a diet rich in processed sugars, known to negatively affect the gut microbiota, might increase the risk for infections like the seasonal flu by preventing migration of colon immune cells.

This study was performed at Harvard Medical School by postdoctoral research fellow Silvia Galván-Peña under the mentorship of Christophe Benoist, Morton Grove-Rasmussen Professor of Immunology and Diane Mathis, Professor of Immunology and Morton Grove-Rasmussen Chair of Immunohematology.

Managing Correspondent: Allegra Carlotta Scarpa

Original Journal Article: A dynamic atlas of immunocyte migration from the gut (Science Immunology)

Related SITN Article: Cooperation vs. Competition: Microbiome Diversity and Interactions

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