Vigilance or Subversion? Constitutive and Inducible M Cells in Mucosal Tissues

Multiple M cell phenotypes from multiple epithelial origins are being identified, but they share convergent apical membrane morphology. Different M cell phenotypes are induced by different conditions, which may indicate functional specialization. M cells capture viruses and bacteria through multiple mechanisms, including electrostatic interactions due to apical surface characteristics, obviating the need for an array of specific capture receptors. Microfold (M) cells are epithelial cells present in mucosal tissues and specialized for the capture of luminal microparticles and their delivery to underlying immune cells; thus, they are crucial participants in mucosal immune surveillance. Multiple phenotypic subsets of M cells have now been described, all sharing a unique apical morphology that provides clues to their ability to capture microbial particles. The existence of diverse M cell phenotypes, especially inflammation-inducible M cells, provides an intriguing puzzle: some variants may augment luminal surveillance to boost mucosal immunity, while others may promote microbial access to tissues. Here, I consider the unique induction requirements of each M cell subset and functional differences, highlighting the potentially distinct consequences in mucosal immunity. Microfold (M) cells are epithelial cells present in mucosal tissues and specialized for the capture of luminal microparticles and their delivery to underlying immune cells; thus, they are crucial participants in mucosal immune surveillance. Multiple phenotypic subsets of M cells have now been described, all sharing a unique apical morphology that provides clues to their ability to capture microbial particles. The existence of diverse M cell phenotypes, especially inflammation-inducible M cells, provides an intriguing puzzle: some variants may augment luminal surveillance to boost mucosal immunity, while others may promote microbial access to tissues. Here, I consider the unique induction requirements of each M cell subset and functional differences, highlighting the potentially distinct consequences in mucosal immunity. lymphoid tissues in the lung airways. conventional intestinal epithelial cells mainly associated with nutrient absorption. lymphoid tissue found in the intestine, including Peyer's patches. inducible lymphoid tissues in the lung airways. immune cells that induce lymphoid stromal cell development. molecules on antigen-presenting cells, such as dendritic cells, that trigger T lymphocyte responses. epithelial cell in intestine or airway that captures bacteria and viruses from the lumen for presentation to mucosal immune cells. lymphoid tissue found in the mucosal tissues, including both airways and intestine. lymphoid tissue found in the upper airway, such as human tonsil. an intestinal lymphoid tissue.