Figure 3.

Entry routes and integrins used by normal lymphocytes (a) Postcapillary venule. In the presence of inflammation, the crossing of the BBB occurs in a manner dependent on VLA-4 (α₄β₁): VCAM-1 and LFA-1 (α_Lβ₂): ICAM-1. (b) Section showing meningeal layers between the calvaria and the brain parenchyma. Lymphocytes may adhere and extravasate from subpial and meningeal vessels, independently of inflammation, using VLA-4: VCAM-1 and LFA-1: ICAM-1. T cells and other immune cells may migrate from calvarial bone marrow into the dura. Whether lymphocytes migrate on emissary vessels and how they cross the arachnoid BCSFB (light blue cell layer) is not known. Whether they interact with cells of the SLYM (green) is also unknown (indicated by question marks). (c) Choroid plexus (CP). Lymphocytes cross the fenestrated capillaries underneath the CP. LFA-1-ICAM-1 has been shown to be involved when T cells cross the ependymal cells (blue) and enter CSF (white). This figure was created with BioRender.com.