Immunopathology at BCSFB. (A) The homeostatic BCSFB expresses TTR, a protein involved in the transport of thyroid hormones and Aβ to the peripheral circulation. The BCSFB is also populated with mitochondria which support this active transport. (B) In MDD, the ChP tight junctions are partially lost, the TTR levels decrease, and chemokine and pro-inflammatory expression increases causing neuroinflammation. (C) In aging or AD, the ChP epithelium is atrophied, the TTR levels severely decline which increases Aβ deposition, decreases metabolic waste efflux, disturbs mitochondrial energetics, and intensifies the infiltration of CD8+ T cells and pro-inflammatory monocytes from the periphery to the CNS.