I have read that neurons have proportionately less MHC molecules than other cells of the body. What is the advantage of this?
Antigen presentation by MHC will induce a cytotoxic response by the immune system, which is usually a good thing in the body since most cells can just divide and replicate again. Neurons, however, are particularly ineffective at regenerating from such an attack, and are not easy to come by; they are also rather important! Better not to risk it, eh?