I have never heard of anything other than a protein to cause immunity responses.

Leaky gut lets thru large molecules that should not be allowed thru. This seems to be a very complicated situation that the body reacts to, as this is an unacceptable invasion. The body has many ways to deal with this, to save itself. To control the exposure, like white blood cells and macrophages, at the very least. Perhaps the reaction to the proteins in the wrong place is as simple as how vaccines work, introduce a foreign protein, and the T cells and Ig's get constructed to stand ready, and the body is armed, for the next invasion.

Im not a pro here-- just putting out ideas from my limited knowledge.