Margins of control: ventricular brain borders as architects in central nervous system autoimmunity

While multiple sclerosis research has long centered on focal demyelinating lesions, it is increasingly recognized that there are distinct, surface-in gradients of diffuse pathology that exist in regions abutting the cerebrospinal fluid (CSF), such as the subpial cortex and periventricular parenchyma. While subpial pathology is thought to possess a relationship with tertiary lymphoid tissues (TLTs) in the meninges, less is known about the pathogenesis of diffuse periventricular pathology. Emerging evidence suggests that periventricular damage may reflect more than passive exposure to inflammatory factors in the CSF; ventricular borders themselves may actively shape disease. The choroid plexus, through vascular, stromal, and epithelial remodeling, may become both a gateway for immune cell entry and a source of cytokines and chemokines that alter CSF composition. In turn, the ependyma-normally a ciliated barrier regulating local CSF flow and CSF-brain exchange-undergoes transcriptional and structural changes that may compromise ventricular barrier integrity, recruit glia, and propagate inflammation into the periventricular parenchyma. Thus, rather than serving as inert borders, these structures appear to orchestrate the accumulation and spread of CSF-borne injury. Viewing the choroid plexus and ependyma as architects in central nervous system autoimmunity reframes diffuse periventricular pathology as a process of border-mediated inflammation, opening avenues for therapeutic strategies targeting these overlooked interfaces.