That's intetesting, i never thought of that before. That's how the immune system works after all though. The only trouble with this theory is that the immune system works on the blood before it gets to the brain. This is ofcourse the bain of every drug user - the 1st and 2nd pass through the liver of an injested chemical, which is why so many of us turn to vaporising, snorting, injecting etc so as to bypass those bastard liver enzymes.
I like your idea though, its logically sound and could well be true, i'm certainly no authority on whats true and whats not.
Also one last thing, i screwed up on the endogenous ligand for the THC receptor. It was discovered back in 1992, a good 10 years before the date that i thought it was. Must have been when i first read about studies using on rats etc.