A new cell-to-cell interaction model for epithelial microfold cell formation and the enhancing effect of epidermal growth factor

Insights into oral lentinan immunomodulation: Dectin-1-mediated lymphatic transport from Peyer's patch M cells to mononuclear phagocytes

Lentinan (LNT), a natural polysaccharide, has been reported to exhibit immunomodulatory effects in the intestine after oral administration. Herein, we aimed to investigate the lymphatic transport of LNT in Peyer's patches (PPs) by traceable fluorescent labeling and to explore whether/how LNT contacts related immune cells. Near-infrared imaging confirmed the absorption of LNT in the small intestinal segment and its accumulation within PPs after oral administration. Subsequently, tissue imaging confirmed that M cells are the main cells responsible for transporting LNT to PPs, and an M cell model was established to explore the involvement of Dectin-1 in the absorption process. Systematic in vitro and in vivo studies revealed that the Dectin-1 further mediates the uptake of LNT by mononuclear phagocytes in PPs. Moreover, LNT can promote the proliferation and differentiation of mononuclear phagocytes, thereby activating immune responses. In summary, this study elucidates the pharmacokinetic mechanisms by which LNT exerts oral immunomodulatory effects, providing a theoretical basis for the development and application of other polysaccharides.

Unlocking the potential of microfold cells for enhanced permeation of nanocarriers in oral drug delivery

The therapeutic effects of orally administered nanocarriers depend on their ability to effectively permeate the intestinal mucosa, which is one of the major challenges in oral drug delivery. Microfold cells are specialized enterocytes in the intestinal epithelium known for their high transcytosis abilities. This study aimed to compare and evaluate two targeting approaches using surface modifications of polymer-based nanocarriers, whereas one generally addresses enterocytes, and one is directed explicitly to microfold cells via targeting the sialyl LewisA motif on their surface. We characterized the resulting carriers in terms of size and charge, supplemented by scanning electron microscopy to confirm their structural properties. For predictive biological testing and to assess the intended targeting effect, we implemented two human intestinal in vitro models containing microfold-like cells. Both models were thoroughly characterized prior to permeation studies with the different nanocarriers. Our results demonstrated improved transport for both targeted formulations compared to undecorated carriers in the in vitro models. Notably, there was an enhanced uptake in the presence of microfold-like cells, particularly for the nanocarriers directed by the anti-sialyl LewisA antibody. These findings highlight the potential of microfold cell targeting to improve oral administration of drugs and emphasize the importance of using suitable and well-characterized in vitro models for testing novel drug delivery strategies.

The construction of in vitro nasal cavity-mimic M-cell model, design of M cell-targeting nanoparticles and evaluation of mucosal vaccination by nasal administration

In order to better evaluate the transport effect of nanoparticles through the nasal mucosa, an in vitro nasal cavity-mimic model was designed based on M cells. The differentiation of M cells was induced by co-culture of Calu-3 and Raji cells in invert model. The ZO-1 protein staining and the transport of fluorescein sodium and dexamethasone showed that the inverted co-culture model formed a dense monolayer and possessed the transport ability. The differentiation of M cells was observed by up-regulated expression of Sialyl Lewis A antigen (SLAA) and integrin β1, and down-regulated activity of alkaline phosphatase. After targeting M cells with iRGD peptide (cRGDKGPDC), the transport of nanoparticles increased. In vivo, the co-administration of iRGD could result in the increase of nanoparticles transported to the brain through the nasal cavity after intranasal administration. In the evaluation of immune effect in vivo, the nasal administration of OVA-PLGA/iRGD led to more release of IgG, IFN-γ, IL-2 and secretory IgA (sIgA) compared with OVA@PLGA group. Collectively, the study constructed in vitro M cell model, and proved the enhanced effect of targeting towards M cell with iRGD on improving nasal immunity.

Cationic Polylactic Acid-Based Nanoparticles Improve BSA-FITC Transport Across M Cells and Engulfment by Porcine Alveolar Macrophages

This work described the development of a cationic polylactic acid (PLA)-based nanoparticles (NPs) as an antigen delivery system using dimethyldioctadecylammonium bromide (DDA) to facilitate the engulfment of BSA-FITC by porcine alveolar macrophages (3D4/2 cells) and heat-labile enterotoxin subunit B (LTB) to enhance the transport of BSA-FITC across M cells. The experimental design methodology was employed to study the influence of PLA, polyvinyl alcohol (PVA), DDA, and LTB on the physical properties of the PLA-based NPs. The size of selected cationic PLA NPs comprising 5% PLA, 5% PVA, and 0.6% DDA with or without LTB absorption was range from 367 to 390 nm with a polydispersity index of 0.26, a zeta potential of + 26.00 to + 30.55 mV, and entrapment efficiency of 41.43%. Electron micrographs revealed NPs with spherical shape. The release kinetic of BSA from the NPs followed the Korsmeyer-Peppas kinetics. The cationic PLA NPs with LTB surface absorption showed 3-fold increase in BSA-FITC transported across M cells compared with the NPs without LTB absorption. The uptake studies demonstrated 2-fold increase in BSA-FITC intensity in 3D4/2 cells with cationic NPs as compared with anionic NPs. Overall, the results suggested that LTB decreased the retention time of BSA-FITC loaded in the cationic PLA NPs within the M cells, thus promoting the transport of BSA-FITC across the M cells, and cationic NPs composed of DDA help facilitate the uptake of BSA-FITC in the 3D4/2 cells. Further studies in pigs with respiratory antigens will provide information on the efficacy of cationic PLA NPs as a nasal antigen carrier system.

Identifying human and murine M cells in vitro

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.

A comparison of three Peyer's patch "M-like" cell culture models: particle uptake, bacterial interaction, and epithelial histology

Intestinal Peyer's patch (PP) microfold (M) cells transport microbes and particulates across the follicle-associated epithelium (FAE) as part of the mucosal immune surveillance system. In vitro human M-like cell co-culture models are used as screens to investigate uptake of antigens-in-nanoparticles, but the models are labour-intensive and there is inter-laboratory variability. We compared the three most established filter-grown Caco-2/Raji B cell co-culture systems. These were Model A (Kernéis et al., 1997), Model B (Gullberg et al., 2000), and Model C (Des Rieux et al. 2007). The criteria used were transepithelial resistance (TEER), the apparent permeability coefficient (P_app) of [¹⁴C]-mannitol, M cell-like histology, as well as latex particle and Salmonella typhimurium translocation. Each co-culture model displayed substantial increases in particle translocation. Truncated microvilli compared to mono-cultures was their most consistent feature. The inverted model developed by des Rieux et al. (2007) displayed reductions in TEER and an increased (P_app), accompanied by the largest increase in particle translocation compared to the other two models. The normally-oriented model developed by Gullberg et al. (2000) was the only one to consistently display an increased translocation of Salmonella typhimurium. By applying a double Matrigel™ coating on filters, altering the medium feeding regime for Raji B cells, and restricting the passage number of B cells, improvements to the Gullberg model B were achieved, as reflected by increased particle translocation and improved histology. In conclusion, this is the first time all three designs have been compared in one study and each displays phenotypic features of M-like cells. While Model C was the most robust co-culture, the Model B protocol could be improved by optimizing several variables and is less complicated to establish than the two inverted models.