M Cells: Intelligent Engineering of Mucosal Immune Surveillance

Abstract

M cells are specialized intestinal epithelial cells that provide the main machinery for sampling luminal microbes for mucosal immune surveillance. M cells are usually found in the epithelium overlying organized mucosal lymphoid tissues, but studies have identified multiple distinct lineages of M cells that are produced under different conditions, including intestinal inflammation. Among these lineages there is a common morphology that helps explain the efficiency of M cells in capturing luminal bacteria and viruses; in addition, M cells recruit novel cellular mechanisms to transport the particles across the mucosal barrier into the lamina propria, a process known as transcytosis. These specializations used by M cells point to a novel engineering of cellular machinery to selectively capture and transport microbial particles of interest. Because of the ability of M cells to effectively violate the mucosal barrier, the circumstances of M cell induction have important consequences. Normal immune surveillance insures that transcytosed bacteria are captured by underlying myeloid/dendritic cells; in contrast, inflammation can induce development of new M cells not accompanied by organized lymphoid tissues, resulting in bacterial transcytosis with the potential to amplify inflammatory disease. In this review, we will discuss our own perspectives on the life history of M cells and also raise a few questions regarding unique aspects of their biology among epithelia.

Intestinal permeability, microbial translocation, changes in duodenal and fecal microbiota, and their associations with alcoholic liver disease progression in humans

“…Inappropriate immune responses and/or transcytosis in the gut, as shown in several situations 26,40 but not investigated in our study, might be one of those mechanisms also implicated in ALD. We found a decreased number of immune cells, such as macrophages and T cells, in the duodenal mucosa of AUD patients as well as little, if any, upregulation of gut-specific pro-inflammatory cytokines.…”

“…DNA extraction and 16 S rRNA library were constructed as described previously. 26 16 S sequence reads were processed using MOTHUR-base 16 S analysis workflow to determine the operational taxonomic units as described previously. 11,27,28 Phyloseq package was used for the α-diversity (observed OTUs, Chao 1, Shannon, and Simpson) and β-diversity (weighted and unweighted Unifrac) analysis.…”

The effects of different dietary fiber pectin structures on the gastrointestinal immune barrier: impact via gut microbiota and direct effects on immune cells

“…Furthermore, the cellular layer contains an additional epithelial cell type called microfold (M) cells, which are present on subepithelial lymphoid structures called Peyer's patches (PP). M cells are specialized antigen sampling cells that present antigens to underlying immune cells in the PP 49 . Together, these epithelial cells form a physical barrier that separates the luminal content from the lamina propria.…”

“…PPs consist of DCs, macrophages, B cells, and T cells. Luminal antigens from the microbiota or dietary components can be taken up through M cells and are presented to subepithelial dendritic cells 49 . DCs present luminal antigens to underlying adaptive immune cells, leading to specific T cell differentiation or the formation of IgA-producing plasma cells 58 .…”

Induction of mucosal immunity against pathogens by using recombinant baculoviral vectors: Mechanisms, advantages, and limitations

“…45 After tethering particulate Ags at their apical surface, M cells endocytose and transcytose them into a basolateral invagination, or pocket, localized in a zone of the lamina propria called subepithelial dome (SED), where cDCs and lymphocytes coexist. 46 The main factor that will determine if MALT produces tolerogenic versus defensive responses is the context in which PAMPs that come along with Ags are sensed by cDCs. 47 The sole presence of PAMPs in mucosae is the "signal 1 ″ to generate a tolerogenic adaptive response, for example, against the microbiota.…”