Something I don't hear talked about enough is the fraction of the immune system that lives in the gut. It's something like 75% depending on what kinds of cells

Something I don't hear talked about enough is the fraction of the immune system that lives in the gut. It's something like 75% depending on what kinds of cells you include. It seems obvious that immune related problems in the periphery would be caused by what the majority of the immune system is dealing with (which is in the gut). Immune cells have state, if they get all fired up in one place and then move somewhere else they can coordinate an inflammatory response elsewhere too. They also send chemical messages called cytokines which can circulate much more quickly and broadly, so that's another mechanism for gut inflammation to transfer to the periphery. That's just the immune cells themselves. There's also chemicals like endotoxin that can leak through the gut barrier into circulation, the immune system creates an inflammatory response to that too, where ever it ends up. This has been called "leaky gut" and was dismissed by the medical community, despite circulating endotoxin and its origin being well understood by researchers.