Fig. 3

Relationship between inflammation and rMDD. Stress is an important factor in the occurrence of depression relapse. Neuroendocrine- and inflammation-related signals generated by gut microbiota and specialized cells within the gut can, in principle, affect the brain and may lead to release of neurotransmitters, excessive activation of microglial cells, increased levels of inflammatory factors from the peripheral nervous system and the central nervous system, release of inflammatory cytokines by immune macrophages, and depressive-like behaviors. CRH corticotropin-releasing hormone, CRP C-reactive protein, HPA hypothalamic–pituitary–adrenal, IL interleukin, TNF-α tumor necrosis factor-α