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Figure 2: Schematic representation of Peyer’s patch organization (also known as gut-associated lymphoid tissue—GALT) shows that the bulk of the tissue is made up by B cells organized in a large and highly active domed follicle. T cells occupy the areas between the follicles. The antigen enters across a specialized epithelium made up of so-called multifenestrated (M) cells. The germinal center is located in the center of the follicle. Cross-section through the Peyer’s patch shows the types of cells and the interactions between the cells of the immune system and the microbiome. M cells: multifenestrated cells; Th-17: T cell helper 17; Treg: T regulatory cells; T cells CD8+: effectors T cells; T helper: naïve CD4+ T cells; B cell; SFB: segmented filamentous bacteria.