The choroid plexus is composed of highly invaginated loops of capillaries and pia mater that reach into the ventricles of the brain. Cells from the blood and under the influence of chemokines undergo adhesion, rolling, and diapedesis across the fenestrated capillary endothelium and pia mater of the choroid plexus. The basement membrane and tight junctions of the choroid plexus epithelium provide a further barrier, the brain-CSF barrier. These modified epithelial cells (Kolmer cells) have bulbous microvilli that secrete the CSF. Infiltrating leukocytes migrating through these cells enter the ventricles that contain CSF and circulate around the CNS. The chemokine CCL20 is expressed on the basolateral side of the choroid plexus epithelial cells, attracting CCR6-expressing CD4⁺ T cells. Chemokines and their receptors demonstrated to be involved in the trafficking of immune cells into the CSF are provided in Table 2.