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M cells (or microfold cells, a name given due to their unique structure) are specialized intestinal epithelial cells that are primarily found overlying gut-associated lymphoid tissue (GALT) lymphoid follicles such as the Peyer’s patches in the ileum (see Image. Epithelial Cells and M Cells). These cells do not possess normal intestinal microvilli, in contrast to normal intestinal enterocytes (epithelial cells), and are specialized to sample macromolecules (antigens and pathogens). M cells function to sample and transport antigens/pathogens from the luminal surface to the sub-epithelium (a process also known as transcytosis), where macrophages and other immune cells process the antigen/pathogens. This is achieved by a unique cellular structure involving many basolateral membrane invaginations that allow for the macrophages and other immune cells to initiate an immune response. M cells play a vital role in immunity, allowing immune responses to occur in response to intestinal pathogens/antigens. It is likely that many, if not all, intestinal antigens are initially processed by M cells. Some note that a decrease in M cells leads to failing immunity, such as in old age or chemotherapeutic states. It has been noted that many pathogens exploit this immune surveillance system, using the M cells as a method to gain access to the bloodstream/other parts of the body. Several intestinal pathogens also specifically target M cells to avoid immune processing. The unique method of M-cell, trans-epithelial transport is also being explored as an intestinal drug and vaccine delivery option. There is still much research being done involving M cells, and it is likely that in 5 years or less, this topic will be further expanded.