Th17 cells sense microbiome to promote depressive-like behaviors

Background: Microbiome alterations have been associated with depression, and fecal transfer of depressed patients’ microbiomes is sufficient to enhance despair behaviors in rodents. Yet little is known about the potential mechanisms, whereby microbes modulate depressive-like behaviors. Results: In this study, we showed that certain bacteria known to induce Th17 cells are increased in depressed patients and mice exhibiting learned helplessness. Fecal transfers of human depressed patients’ microbiomes into germ-free-like mice were sufficient to decrease sociability and increased susceptibility to the learned helplessness paradigm, confirming that the microbiome is sufficient to confer depressive-like behaviors. This microbial effect was dependent on the presence of Th17 cells in the recipient, as germ-free-like recipient mice deficient in Th17 cells were resistant to the behavioral changes induced by the microbiome of depressed patients. Conclusion: Altogether, these findings suggest a crucial role of the microbiome/Th17 cell axis in regulating depressive-like behaviors. [MediaObject not available: see fulltext.]