English: Intestinal microenvironments and niches.  The intestine is exposed to constant luminal stimulation and harbors a dense and very diverse set of immune cells. Different layers of the intestinal tissue and regions along the gastrointestinal tract are subjected to particular stimuli, which are coupled with site-specific adaptation of immune cell subsets. The figure depicts the main characteristics of the intestinal layers, proximal-distal regions and immune cells populations exposed to chronic stimulation by dietary and microbial antigens. Although stimulation by dietary antigens or metabolites decreases from proximal to distal intestine, microbial stimulation follows the opposite direction. An approximate illustration of the changes in abundance of each cell type per intestinal region is shown on the bottom.