Blood-Brain Barrier (BBB)

**What it means:** The BBB is an ultra-tight layer of cells lining the brain's blood vessels. Think of it like a **super-filter** or a nightclub with an extremely strict bouncer — it lets nutrients and oxygen through but blocks almost everything else, including most drugs. It exists to protect the brain from toxins and infections. **Why it matters for MHS treatments:** Any drug that targets microglia (brain immune cells) or neurons **must** cross the BBB. Most drugs in development never get a chance to do this because they can't penetrate the barrier. AL-605 was specifically engineered (via structure-guided drug design) to cross the BBB — it's like the drug was given "VIP access" to the brain club. This is a genuine engineering breakthrough, not a minor tweak.