There is a response by our immune system that has been noted by numerous researchers. It involves an immune cell type called microglia that turn on when a threat is detected and then turn off. But under certain conditions the "off" order is ignored and the inflammatory response continues. In one example, a mouse was given a shot of a bacterial toxin in a limb that triggered inflammation. A few hours later, the toxin was eliminated and the immune system packed its bags and called it a day in the affected limb.

But in the animal's brain the immune system kept rolling at full speed and was still going *ten months* later. And the majority of the rodent's substanta nigra had been wiped out. The chemicals produced in the process are cytokines and TNF-alpha mentioned is one of these.

In a sense, our brains really are on fire. In slow motion, yes, but a new infection throws more fuel on as in the case of the AD patients.