Fig. 1. Immune dysregulation associated with MDD.
a | In the periphery, a variety of immune markers have been associated with major depressive disorder (MDD). These include elevation of pro-inflammatory cytokines, increases in innate immune cell types and changes in differentiation of T cells and other immune cell types. Direction of change of expression or cell count in MDD indicated with an arrow. b | In the central nervous system (CNS), elevation of pro-inflammatory cytokines is observed in the cerebrospinal fluid (CSF), which may come from the periphery — entering the CNS through the blood–brain barrier (BBB; indicated in centre of figure) or the dural lymphatic system — or be produced from cells within the CNS, including glia. An increase in activated microglia, the resident macrophages in the CNS, in MDD has been implicated by imaging and post-mortem studies and is a current biological target of interest. Breg cell, regulatory B cell; HSC, haematopoietic stem cell; IFN, interferon; ILC, innate lymphoid cell; ROS, reactive oxygen species; Tc cell, conventional T cell; TH1 cell, T helper 1 cell; Treg cell, regulatory T cell; TGFβ, transforming growth factor-β; TNF, tumour necrosis factor.