...I've been studying gut and digestive health for a very long time. There are some complex mechanisms involved that are not very well understood, especially with things like auto-immunity conditions and chronic digestive system disorders.
That said, the principle still applies: Simple composition yields complex manifestations.
Recently, scientists had to acknowledge that they needed to rewrite the text books on the lymphatic system when researchers discovered that the brain DOES indeed have a lymph system tied directly to the gut.
Now, with this new analytical device (below), perhaps scientists can begin to understand both the simplicity of the immune system, and the complexity of its expressions.
That's the hope!
https://futurism.com/swallowable-sensor-transform-understanding-human-gut/