Well here is what I think of some of what is going on. With a lot of speculation.
Your commensal microbiome from when you are born is recognized as self by the immune system.
Once it penetrates the gut lining it is none self.
Appendix is now thought to hold commensal bacteria to possibly re-inoculate the bowel flora.
If you have the appendix removed it is protective for UC,perhaps when you get UC there is also a breach
in the appendix making commensals none self. Wild guess.
After UC if removed not protective,I can see this happening since the gut bacteria are now none self.
Even in identical twins the microbiome is different.
How might FMT help after UC onset.
Well it supplies new commensal bacteria,plus phages/fungi/viruses,which are of course none self.
If none self how the hell can it work, in some.
Self or none self does not matter perhaps.
FT corrects missing bacteria,or kills off pathogens,or corrects ratios, that enables the mucosal breach to heal,
perhaps by elimination bacteria that express too much protease,or enables the inactivation of excess digestive
protease via the new bacteria,correct too many butyric acid producing bacteria, all of the above plus much more.
Why would FT make someone sicker,perhaps the wrong bacteria that does not do the above.
How can too much butyric acid cause a problem,it is a toxin at high concentration.
How can some go into remission just by bowel prep.
Reduces the bacterial, load/toxins/proteases,allows the mucus barrier to recover and exclude bacteria.
Since I know of two protease inhibitors that can put humans into remission, excess protease is involved.
Speculative story of the day.
Post Edited (Old Mike) : 9/23/2014 2:38:31 PM (GMT-6)