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. Author manuscript; available in PMC: 2010 Jan 29.
Published in final edited form as: Nat Rev Immunol. 2009 Jun;9(6):393. doi: 10.1038/nri2550

Figure 1. Anatomical organization of the brain showing the possible routes of activated T cell entry.

Figure 1

Activated T cells can enter the subarachnoid space by migrating from blood vessels into the stroma of the choroid plexus and then crossing the blood–cerebrospinal fluid (CSF) barrier surrounding the choroid plexus stroma, which comprises epithelial cells joined by tight junctions. Activated T cells can also enter the subarachnoid space by extravasating through the cell wall of meningeal venules, which consists of endothelial cells connected by tight junctions. In addition, activated T cells can cross the blood–brain barrier surrounding post-capillary venules that penetrate the brain parenchyma, which comprises endothelial cells connected by tight junctions. T cells crossing the blood–brain barrier enter the perivascular space, which is the region between the basement membrane connected to the blood vessel endothelial cells and the glial limitans (which is composed of astrocyte feet and microglial cell; not shown).