This lining, it was thought, kept our microbiota from getting into the rest of the body and thus away from the immune system. This theory is called immunological ignorance. The immune cells, in effect, were thought to be ignorant of these bacteria among us. This thinking was incomplete, if not outright incorrect. Mazmanian and others have since found that the gel that lines the gut is colonized by the microbiota, and their presence puts them very much in close proximity to cells that can trigger an immune response. On the other side of that gel-like wall is a line of cells, called epithelial
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