**3.4 M cells**

M cells or Microfold cells (because of uneven microvilli) are classified as epithelial cells with large fenestrations in their membranes. These features enhancing the uptake of antigens from the gut lumen [38]. They have a capability for capturing luminal antigens and transporting them across the epithelium ("transcytosis"). They are placed in the gut epithelium called follicle associated epithelium overlying the domes of Peyer's patches and other lymphoid organs. M cells are not professional antigen-presenting cells because they do not have the ability to process and present antigens to the major histocompatibility complex (MHC) molecules. Instead, they serve as antigen delivery cells, that is, as a functional equivalent to lymphoid nodes because they provide antigens to professional antigen-presenting cells, such as dendritic cells (DCs), macrophages as well as B lymphocytes. Indeed, many pathogens take advantage of their transport efficacy to invade the body [39–41]. M cells subsequently transfer these antigens to underlying DCs enabling the transfer of captured molecules through transcytosis mechanism (which remain to be elucidated) as well as intracellular material through microvesicles to underlying DCs [42]. In conclusion, M cells provide specialized full-service immune surveillance capabilities.
