Laboratory of Histology and Cytology, Graduate School of Medicine, Hokkaido University, Sapporo, Japan.
Division of Biochemistry, Faculty of Pharmacy, Keio University, Tokyo, Japan.
Front Immunol. 2019 Jun 11;10:1323. doi: 10.3389/fimmu.2019.01323. eCollection 2019.
Microfold (M) cells residing in the follicle-associated epithelium of mucosa-associated lymphoid tissues are specialized for sampling luminal antigens to initiate mucosal immune responses. In the past decade, glycoprotein 2 (GP2) and Tnfaip2 were identified as reliable markers for M cells in the Peyer's patches of the intestine. Furthermore, RANKL-RANK signaling, as well as the canonical and non-canonical NFκB pathways downstream, is essential for M-cell differentiation from the intestinal stem cells. However, the molecular characterization and differentiation mechanisms of M cells in the lower respiratory tract, where organized lymphoid tissues exist rarely, remain to be fully elucidated. Therefore, this study aimed to explore M cells in the lower respiratory tract in terms of their specific molecular markers, differentiation mechanism, and functions. Immunofluorescence analysis revealed a small number of M cells expressing GP2, Tnfaip2, and RANK is present in the lower respiratory tract of healthy mice. The intraperitoneal administration of RANKL in mice effectively induced M cells, which have a high capacity to take up luminal substrates, in the lower respiratory epithelium. The airway M cells associated with lymphoid follicles were frequently detected in the pathologically induced bronchus-associated lymphoid tissue (iBALT) in the murine models of autoimmune disease as well as pulmonary emphysema. These findings demonstrate that RANKL is a common inducer of M cells in the airway and digestive tracts and that M cells are associated with the respiratory disease. We also established a two-dimensional culture method for airway M cells from the tracheal epithelium in the presence of RANKL successfully. This model may be useful for functional studies of M cells in the sampling of antigens at airway mucosal surfaces.
黏膜相关淋巴组织中的黏膜上皮滤泡相关上皮中的微褶皱(M)细胞专门用于采样腔抗原以启动黏膜免疫反应。在过去的十年中,糖蛋白 2(GP2)和 Tnfaip2 被鉴定为肠道派尔集合淋巴结中 M 细胞的可靠标志物。此外,RANKL-RANK 信号以及下游的经典和非经典 NFκB 途径对于肠干细胞分化为 M 细胞是必不可少的。然而,在组织淋巴组织很少存在的下呼吸道中,M 细胞的分子特征和分化机制仍有待充分阐明。因此,本研究旨在探索下呼吸道中的 M 细胞在其特异性分子标志物、分化机制和功能方面的特征。免疫荧光分析显示,健康小鼠的下呼吸道中存在少量表达 GP2、Tnfaip2 和 RANK 的 M 细胞。在小鼠中腹腔内给予 RANKL 可有效诱导下呼吸道上皮中的 M 细胞,这些细胞具有摄取腔底物的高能力。在自身免疫性疾病和肺气肿的小鼠模型中,与淋巴滤泡相关的气道 M 细胞经常在气道相关淋巴组织(iBALT)中被检测到。这些发现表明 RANKL 是气道和消化道中 M 细胞的共同诱导剂,并且 M 细胞与呼吸道疾病有关。我们还成功地建立了一种在 RANKL 存在的情况下从气管上皮分离气道 M 细胞的二维培养方法。该模型可能有助于研究气道黏膜表面抗原采样中 M 细胞的功能。