Once an immune system is "primed" to over react,an infection outside the BBB can trigger the destruction within it. Periodontal disease should constitute a chronic, always present trigger. So the microglia are always active. There is another side to this as well. The cytokines produced by the microglia are themselves destructive and perpetuate inflammation. But they are also, themselves, neurotransmitters. Even in normal folk, when your immune system starts cranking up the cytokines, your brain takes a vacation and your immune system takes over and sends you to bed. The chemistry is not neutral.

Finally, your body has a response to inflammation. It releases a chemical that signals the immune system to cut back and start to wind things down. Unfortunately, the chemical is cortisol which, as a chronic problem, is destructive in its own right. PWP typically have elevated cortisol.

So, all from inflammation, we have self destructive action of the microglia plus interference with normal function plus elevated cortisol.