good post - not sure if you covered the glutathione (cysteine) depletion caused by mercury - cysteine & glutathione are essential for immune system health as well as detoxification properties - best form of glutathione is liposomal, I would caution you to go slow -
If mercury is not the problem then look at pathogenic organisms such as protozoa or rogue bacteria - Metametrix GI Effects is the the #1 test for this - use panel #2105