When it comes to defending the brain from parasites, the immune system, if not kept under tight control, can actually do more harm than good. The brain is immunologically privileged: it is protected from outside threats by both the blood-brain barrier, a tightly-packed layer of cells that allows only certain molecules to enter the brain from the bloodstream, and by specialized immune cells located inside the barrier. When the brain comes under siege by parasites, immune cells from the bloodstream are recruited to the area to help attack the invaders. This flooding of immune cells into the tissue surrounding the brain damages the cells in the blood-brain barrier, inadvertently allowing more parasites into the brain. Olivera et al. show that nitric oxide helps prevent immune cells from overwhelming the blood-brain barrier. When immune cells first reach the brain from the bloodstream, they stimulate immune cells in the brain to produce nitric oxide. As more nitric oxide is produced, it inhibits signaling molecules that would normally recruit additional immune cells to the brain. This negative-feedback loop ensures that some immune cells arrive to provide additional defenses for the brain, but not so many that damage is caused to the fortification keeping the parasites at bay.
- Stephanie DeMarco
Staff Writer, Signal to Noise Magazine
PhD Candidate, Molecular Biology