In the past, we've mostly looked at bile acids in the context of bile acid malabsorption (BAM). BAM is a common cause of diarrhea in microscopic colitis (MC) patients who don't respond to any of the treatments that are usually effective. But some interesting research demonstrating that bile acids appear to help regulate gut immunity and inflammation has recently been published. (1)
Basically, the study showed that bile acids are modified by gut bacteria to regulate certain types of immune cells that in turn, regulate inflammation. The gallbladder dribbles bile acids into the common bile duct in the duodenum to help dissolve fats in the diet. Farther down the gastrointestinal tract, gut bacteria convert bile acids into two types of immune cells by creating certain metabolites that favor the promotion of T cells (Tregs) and helper T cells (Th17 cells). T cells suppress inflammation, while Th17 cells promote inflammation.
Normally, the T cells and Th17 cells are balanced so that stability is maintained in the intestines. If some type of insult causes intestinal damage (such as a non-IBD issue), then normally the cellular damage is healed by first utilizing Th17 cells to initially promote inflammation (which allows various white cells from the immune system to destroy any invaders and damaged cells). After the damaged cells and any other foreign matter are removed, then T cells replace the Th17 cells, to suppress inflammation and allow the healing process to be completed.
But as we know, when MC is untreated, the damage never ends (because the dietary insults never end), so healing can never be completed and the inflammation is perpetuated. This leads to altered gut bacteria population profiles because of the resulting compromised digestion. It's likely that this effect might favor increases in Th17 numbers, thus promoting inflammation, just as the research suggests. But because healing can never be completed (without treatment intervention), it's unlikely that a condition would ever be reached where Tregs would be promoted by the process. This suggests that MC patients would still be better off by getting rid of (sequestering) as much bile acid as possible, simply because the net total effects of bile acids on MC appear to be predominantly negative.
After all, just because T cell regulation is normally within the scope of influence of bile acids doesn't mean that bile acids will be helpful in the treatment of MC (or any other IBD). It appears that this research merely confirms what we already knew (that Tregs are suppressed, and pro-inflammatory T cells are promoted) whenever an IBD develops, or an existing case becomes active. However, the research does make a novel contribution to the knowledge base by verifying a mechanism (gut bacteria acting on bile acids) to explain how the perpetuated inflammation may occur.
1. Harvard Medical School. (2020, January 3). Bile acids may help regulate gut immunity and inflammation. Retrieved from: https://www.sciencedaily.com/releases/2020/01/200103141047.htm