Epithelial M Cells: differentiation and function.

M cells are distinctive epithelial cells that occur only in the follicle-associated epithelia that overlie organized mucosa-associated lymphoid tissues. They are structurally and functionally specialized for transepithelial transport, delivering foreign antigens and microorganisms to organized lymphoid tissues within the mucosae of the small and large intestines, tonsils and adenoids, and airways. M cell transport is a double-edged sword: Certain pathogens exploit the features of M cells that are intended to promote uptake for the purpose of immunological sampling. Eludication of the molecular architecture of M cell apical surfaces is important for understanding the strategies that pathogens use to exploit this pathway and for utilizing M cell transport for delivery of vaccines to the mucosal immune system. This article reviews the functional and biochemical features that distinguish M cells from other intestinal cell types. In addition it synthesizes the available information on development and differentiation of organized lymphoid tissues and the specialized epithelium associated with these immune inductive sites

Collaboration of epithelial cells with organized mucosal lymphoid tissues

Immune surveillance of mucosal surfaces requires the delivery of intact macromolecules and microorganisms across epithelial barriers to organized mucosal lymphoid tissues. Transport, processing and presentation of foreign antigens, as well as local induction and clonal expansion of antigen-specific effector lymphocytes, involves a close collaboration between organized lymphoid tissues and the specialized follicle-associated epithelium. M cells in the follicle-associated epithelium transport foreign macromolecules and microorganisms to antigen-presenting cells within and under the epithelial barrier. Determination of the earliest cellular interactions that occur in and under the follicle-associated epithelium could greatly facilitate the design of effective mucosal vaccines in the future