Sadly, we've all been subconsciously conditioned to believe something like this from The Princess Bride scene where Wesley built up an immunity to Iocane powder. :/
A cutting edge treatment for nut allergies is to consume small amounts of nuts (carefully prepared, etc.).
edit: I want to differentiate the nut thing from homeopathy. The idea there is to consume a very small and carefully measured portion of the nut, not some nonsense about training molecules.
It makes total sense for nut allergy where the disease is the intolerance; if you become immune to the substance you are cured.
Toothache is not an intolerance to deadly nightshades and no level of resistance to the poison will cure what is a totally unrelated issue; pain caused by a something slowly digging a hole through my gum.