Peptides are proteins, and in a person with the genetic potential to overreact to invading proteins in the blood (gluten is one example)...you can react to your own if they are found floating around like an invader, and not attached to where they belong.

It is one theory for some viral illness triggers for PN.
This is not common, and no one yet has proven the theory but some doctors will cite it to patients when other answers are negative.

B12 injections are typically cyano form, and for those who have the methylation genetic errors is not going to work as they cannot activate to methylcobalamin for the B12 to be in it active form.

Better to take methyB12 orally for a while and see if that improves things. At least 1mg a day on an empty stomach.

Well, thank you Mrs D, that's a really helpful response! I am an allergic to proteins in wheat in particular and to gluten (not officially coeliakie, but an integral doctor found I was allergic to this). I also have a cow milk protein allergy. I had irritable bowel syndrom for a couple of years and this got better with a wheat, gluten and cow milk free diet (although western medicine doctors couldn't find any of these allergies!).

But now to the PN. I can imagine that the process you describe was en is happening in my body. But is there any way to stop this process? I've read about IVIG. Would that be a possibility? I don't want to get my hopes up to much, but just want to explore the possibilities.

I will take the methylcobalamin.