The “6B” Strategy: Build Back a Better Blood–Brain Barrier

Under pathological conditions such as multiple sclerosis (MS), leukocytes infiltrate the central nervous system where they, in concert with activated microglia, promote inflammatory demyelination resulting in a broad spectrum of symptoms, including paralysis. Therefore, all current therapeutic approaches to MS target the immune system, blocking inflammation and paralysis progression, but may compromise the immune system. In this focused review, we present an underestimated compartment, the blood–brain barrier, which is compromised during MS and becomes permeable to leukocytes infiltrating the central nervous system. This barrier has the potential to offer new therapeutic strategies and is easily accessible for drugs. We highlight this paradigm using the example of the therapeutic anti-Reelin strategy we have developed. Reelin is a plasma protein that regulates the expression of adhesion markers on the endothelial surface, thus promoting the infiltration of inflammatory cells and propagating inflammation. Building Back a Better Blood–Brain Barrier (the “6B” strategy) may have advantages compared to actual immunosuppressive drugs because it restores a physiological function rather than suppressing the immune system.