Figure 1. Early life stress (ELS) contributes to the development of depression through the endocrine system, immune system and gut microbiota. ELS can lead to high reactivity of HPA axis response to stress and the disorder of HPA axis is closely related to the development of depression. The imbalance of immune system caused by the disorder of glucocorticoid secretion and the change of gut microbiota are also related to the development of depression. Abbreviations: GR: glucocorticoid receptor; TLR: Toll-like receptor; GRF: corticotropin releasing factor; ELS: early life stress; 5-HT: 5-hydroxytryptamine; IL-1: interleukin-1; IL-6: interleukin-6; IL-10: interleukin-10; IL-18: interleukin-18; BDNF, brain-derived neurotrophic factor; SCFA: short-chain fatty acid; AG: adrenal glucocorticoid; GSK3: Glycogen synthase kinase 3; NF-κB: nuclear factor-κ -gene binding.