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12 Headlines THE SECRETS ENCIRCLING YOURBRAIN And how it could help treat diseases like Alzheimer’s and Parkinson’s Dr Justin Rustenhoven is among the few scientists at the Neurological Foundation Human Brain Bank to, technically, not study the brain. H e is fascinated by the brain’s outer protective casing, a relatively unexplored region that may hold secrets to fighting brain disease. The skull, for instance, is packed with a rich layer of bone marrow full of immune cells and disease-fighting properties. Justin has started the Brain Bank’s first precious collection of tissue from the brain’s outer dura mater, with a view to expanding to skull fragments. “The brain floats in a sac of cerebrospinal fluid, held in place by the meninges, then the skull,” says Justin. “The dura is the outermost layer of the meninges and it looks like a thick piece of leather, or a deflated soccer ball. It’s crazy to think you have that sitting inside your head.” The Brain Bank holds almost no surrounding tissue, and no skull fragments, since it started receiving donations 30 years ago. Justin says up until now there hasn’t been much interest in it from a research perspective. That changed in 2015 when American scientists discovered a previously unknown link between the brain and the immune system, sitting just below the skull in the thick dura layer. Justin is New Zealand’s foremost expert on the recent finding, having completed his post-doctorate at the University of Virginia’s Kipnis lab, which made the discovery. Here he worked directly under renowned neuroscientist and immunologist Professor Jonathan Kipnis, and when the Kipnis lab shifted to the University of Washington in St Louis, Justin joined them for two years before returning to New Zealand. “We thought we had human anatomy mapped out, right?” Justin exclaims. “And then we discover this network of lymphatic vessels we didn’t even know existed!” The breakthrough helped overturn the accepted dogma of central nervous system immune privilege – that the immune system is unable to interact with the brain, because the brain is so effective at keeping invaders out. While the brain and immune systems mostly operate independently, scientists now know they ‘talk’ to each other. The finding has been hailed as the “missing link” between the immune system and the brain, and opens exciting possibilities for treating neurological disease. The lymphatic system is part of the immune system, Justin explains, so the presence of lymphatic vessels beneath the skull that can drain brain waste confirms the immune system is keeping an eye on the brain. Additionally, his research has demonstrated that the skull and dura also harbour diverse populations of immune cells under steady state conditions. “So we have immune cells sitting within the skull bone marrow and the dura mater, not in the brain itself, just patrolling and waiting to be called up to fight. When there’s Dr Justin Rustenhoven