IDO1 and major depressive disorder: A mouse model of depression demonstrated attenuation of anxiety-like behaviors induced by chronic mild stress, an increase in Lactobacillus abundance, and the reversal of stress-induced immune changes in the hippocampus by affecting IFN- γ, TNF-α, and indoleamine 2,3-dioxygenase-1 levels with the supplementation of a multistrain probiotics treatment (L. helveticus R0052, L. plantarum R1012, and B. longum R0175), which suggests that the gut microbiota–inflammation–brain axis is a possible target for alleviating anxiety and depression [128].