In the version of this article initially published, the figure that depicted the main sites of immune cell entry into the brain parenchyma contained some anatomical details that we felt might lead to confusion among the nonspecialist readership. The central region of the brain parenchyma was unlabeled and not colored as parenchyma, and the subarachnoid space that surrounds the cerebellum was not indicated. These omissions have been rectified. In addition, the folded epithelial cell layer lining the choroid plexus had been depicted projecting into the unlabeled central region. We now show this cell layer extending into the ventricle. The figure legend has also been updated to indicate that cells reach the CSF in the first route by crossing through the fenestrated blood vessels of the choroid plexus. The errors have been corrected in the HTML and PDF versions of the article.