Impacts of Early Life Adversity on Microbiota and Immune Functioning in Individuals with Major Depressive Disorder

Early life stress may contribute to depression vulnerability, possibly through immune system development and gut microbial colonization patterns. Increased pro-inflammatory cytokines and differences in gut microbiota composition have been seen in depressed individuals. The current study investigated inflammatory and bacterial profiles of 39 individuals with a current major depressive episode and 43 healthy volunteers with varying severity of childhood trauma. Plasma interleukin (IL)-6/IL-10 ratios was positively correlated with depression severity, and childhood trauma explained variance in severity of symptoms above and beyond that accounted for by the IL-6/IL-10 ratios. Expression of Faecalibacterium prausnitzi (F. prausnitzi) in stool was decreased in depressed participants compared to healthy controls. Importantly, this relationship was significant only in participants who had experienced moderate-to-severe physical neglect. These findings suggest a relationship between particular gut bacteria and depressive symptoms that is dependent on the presence of specific types of early life trauma.