Epithelial barrier and antigen uptake in lymphoepithelium of human adenoids

Abstract

Invasion of antigens through the mucosal surface can be prevented by the common mucosal immune system, including Peyer's patches (PPs) and nasopharyngeal-associated lymphoreticular tissue (NALT). The adenoids (nasopharyngeal tonsils) comprise one of the NALTs and constitute the major part of Waldeyer's lymphoid ring in humans. However, the role of the lymphoepithelium, including M cells and dendritic cells (DCs), in the adenoids is unknown compared with the epithelium of PPs. NALTs also have unique functions such as the barrier of epithelial cells and uptake of antigens by M cells and DCs, and may play a crucial role in airway mucosal immune responses. The lymphoepithelium of adenoids has well-developed tight junctions that play an important role in the barrier function, the same as nasal epithelium but not palatine tonsillar epithelium. Tight junction molecules are expressed in both M cells and DCs as well as epithelial cells, and various antigens may be sampled, transported, and released to lymphocytes through the cells while they maintain the integrity of the epithelial barrier. This review summarizes the recent progress in our understanding of how M cells and DCs control the epithelial barrier in the adenoids.

Keywords::

• NALT
• epithelial cells
• tight junction
• M cells
• dendritic cells
• Toll-like receptors

Acknowledgments

We thank Ms Emi Suzuki and Ms Yukie Takamura for their technical support, Dr Katsushi Asano (KKR Sapporo Medical Center Tonan Hospital) and Dr Yukihiro Somekawa (Sapporo Hospital of Hokkaido Railway Company) for their material support. We specially thank Professor Emeritus Akikatsu Kataura and his colleagues for their great work and valuable suggestions. This work was supported by Grants-in-Aid from the National Project “Knowledge Cluster Initiative” (2nd stage, “Sapporo Biocluster Bio-S”) Program for developing the supporting system for upgrading education and research, the Ministry of Education, Culture, Sports Science, and Technology, and the Ministry of Health, Labour and Welfare of Japan.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.