The potential to develop an autoimmune disease is thought today to be inherited. So yes, it is always there for some people.

The leaky gut issue, is one way to develop one. There are spaces between the GI lining's cells called Zonulin channels.
It these are open, then large peptides (allergenic proteins) can leak into the blood and stimulate antibodies.

There was a study in 1999 that suggested NSAIDs block the Cox-2 protections in the GI tract that keep out peptides as well. So using drugs to block Cox-2 is thought to increase food allergies and intolerances. The study did not prove 100% but it was highly suggestive of the role of NSAIDs in promoting leaky gut.

The non medication suggestions however are not 100% effective either. There is not much in medicine that is 100% for trestments.