Identifying human and murine M cellsin vitro

Abstract

M cells are an epithelial cell population found in the follicle-associated epithelium overlying gut-associated lymphoid tissues. They are specialized in the transcytosis of luminal antigens. Their transcytotic capacity and location in an immunocompetent environment has prompted the study of these cells as possible targets for oral drug delivery systems. Currently, the models most commonly used to study M cells are restricted to in vivo experiments conducted in mice, and in vitro studies conducted in models comprised either of primary epithelial cells or established cell lines of murine or human origin. In vitro models of the follicle-associated epithelium can be constructed in several ways. Small intestinal Lgr5+ stem cells can be cultured into a 3D organoid structure where M cells are induced with RANKL administration. Additionally, in vitro models containing an “M cell-like” population can be obtained through co-culturing intestinal epithelial cells with cells of lymphocytic origin to induce the M cell phenotype. The evaluation of the efficiency of the variations of these models and their relevance to the in vivo human system is hampered by the lack of a universal M cell marker. This issue has also hindered the advancement of M cell-specific targeting approaches aimed at improving the bioavailability of orally administered compounds. This critical review discusses the different approaches utilized in the literature to identify M cells, their efficiency, reliability and relevance, in the context of commonly used models of the follicle-associated epithelium. The outcome of this review is a clearly defined and universally recognized criteria for the assessment of the relevance of models of the follicle-associated models currently used. Impact statement The study of M cells, a specialized epithelial cell type found in the follicle-associated epithelium, is hampered by the lack of a universal M cell marker. As such, many studies lack reliable and universally recognized methods to identify M cells in their proposed models. As a result of this it is difficult to ascertain whether the effects observed are due to the presence of M cells or an unaccounted variable. The outcome of this review is the thorough evaluation of the many M cell markers that have been used in the literature thus far and a proposed criterion for the identification of M cells for future publications. This will hopefully lead to an improvement in the quality of future publications in this field.

Single-Cell Transcriptomics-Based Study of Transcriptional Regulatory Features in the Non-Obstructive Azoospermia Testis

“…We identified specific TFs including POU2F2, SPIB, IRF5, CEBPA, ELK4 and KLF6 in iNOA tMΦ. Among these identified TFs, both POU2F2 and SPIB are essential for cell proliferation, differentiation and functional maturation of immune cells ( Hodson et al, 2016 ; Klisuric et al, 2019 ). IRF5 has been shown to act as a master switch that promotes proinflammatory cytokine production from macrophages and thus contributes to the plasticity of macrophage polarisation ( Banga et al, 2020 ).…”

The in vitro gastrointestinal digestion-associated protein corona of polystyrene nano- and microplastics increases their uptake by human THP-1-derived macrophages

“…In vivo, the intestinal uptake of most MNPs is thought to be facilitated by M-cells, which have a high phagocytotic capacity [ 32 ]. Yet current cell culture protocols cannot produce M-cells in the absence of other cell types, and no protocols are available that generate M-cells that show surface marker expression similar to that of in vivo M-cells [ 30 , 33 ]. For this reason, we decided to use a THP-1-derived macrophage model emulating tissue-resident macrophages that are located downstream of M-cells and thus represent a highly exposed cell population.…”

The in vitro gastrointestinal digestion-associated protein corona of polystyrene nano- and microplastics increases their uptake by human THP-1-derived macrophages

“…In vivo, the intestinal uptake of most MNPs is thought to be facilitated by M-cells, which have a high phagocytotic capacity (32). Yet current cell culture protocols cannot produce M-cells in the absence of other cell types, and no protocols are available that generate M-cells that show surface marker expression similar to that of in vivo M-cells (33)(34)(35). For this reason, we decided to use a THP-1-derived macrophage model emulating tissue-resident macrophages that are located downstream of M-cells and thus represent a highly exposed cell population.…”