There's something special about LPS though
 

It's not just the normal inflammation response that is important in PD. LPS, in certain individuals, triggers the defences of the brain itself. The immune response there is to activate the microglia which act against invaders. Unfortunately, in PD they don't turn off normally and slowly attack the neurons themselves. The result is a slow burn that gradually eliminates large chunks of mental real estate.

But again, we need to get past the "single cause" approach and that is more difficult than I would have thought.