TNF and major depressive disorder: Additionally, cytokines, such as TNFα, also can disrupt BBB permeability, raising the possibility that increased BBB permeability caused by microglia-derived cytokines contributes to depression (Menard et al., 2017; Cheng et al., 2018) by promoting the infiltration of peripheral inflammatory molecules and immune cells (Wohleb et al., 2011, 2013).