[The intestinal microbiota: A new player in depression?]

Depression is the leading cause of disability in the world according to the World Health Organization. The effectiveness of the available antidepressant therapies is limited. Data from the literature suggest that some subtypes of depression may be associated with chronic low grade inflammation. The uncovering of the role of intestinal microbiota in the development of the immune system and its bidirectional communication with the brain have led to growing interest on reciprocal interactions between inflammation, microbiota and depression. Our purpose is to review the state of knowledge on these interactions.

We carried out a literature search on Pubmed, Go pubmed, psyC info, Elsevier, Embase until August 13, 2016 using the keywords "depression", "microbiota" and "inflammation".

Dysbiosis reported in patients suffering from depression seems to contribute to low grade systemic inflammation which in turn feeds back depression. The hypothetical mechanisms behind these interactions are multiple: leaky gut, hyperreactivity of the corticotropic axis, disturbed neurotransmission. Abnormal microbial exposure during childhood and perinatal stress are reported to influence both the maturation of the immune system and the microbiota hence contributing to the ethiopathogeny of depression. There is no evidence in the literature to support a role for diet.

The evidence supporting a causal relationship between dysbiosis and depression through low grade inflammation is limited and precludes us from drawing firm conclusions. Further studies are needed to improve our knowledge.