In MDD, increases in pro-inflammatory cytokines, such as IL-6 and TNF-α, are related to hyperactivity of the hypothalamic–pituitary–adrenal axis, which consequently stimulates the secretion of corticotropin-releasing hormone and adrenocorticotropic hormone and secondarily stimulates the secretion of glucocorticoids11,12. Here, TNF is linked to major depressive disorder.