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

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.