M cell-derived vesicles suggest a unique pathway for trans-epithelial antigen delivery

Abstract

M cells are a subset of mucosal epithelial cells with specialized capability to transport antigens across the mucosal barrier, but there is limited information on antigen transfer in the subepithelial zone due to the challenges in tracking microparticles and antigens that are transcytosed by this unique cell. Using transgenic reporter mice expressing dsRed in the cytoplasm of M cells and EGFP in myeloid cells, we observed that the M cell basolateral pocket hosts a close interaction between B lymphocytes and dendritic cells. Interestingly, we identified a population of previously undescribed M cell-derived vesicles (MCM) that are constitutively shed into the subepithelial space and readily taken up by CX₃CR1⁺CD11b⁺ CD11c⁺ dendritic cells. These MCM are characterized by their cytoplasmic dsRed confirming their origin from the M cell cytoplasm. MCM showed preferential colocalization in dendritic cells with transcytosed bacteria but not transcytosed polystyrene beads, indicating a selective sorting of cargo fate in the subepithelial zone. The size and number of MCM were found to be upregulated by bacterial transcytosis and soluble toll-like receptor 2 (TLR2) agonist, further pointing to dynamic regulation of this mechanism. These results suggest that MCM provide a unique function by delivering to dendritic cells, various materials such as M cell-derived proteins, effector proteins, toxins, and particles found in the M cell cytoplasm during infection or surveillance.

Keywords:

• cytoplasm
• M cell
• PGRP-S-dsRed/CX₃CR1-EGFP double transgenic mice
• Peyer's patch
• immune surveillance
• vesicle

Abbreviations:

• MCM, M cell-derived microvesicle
• TLR2, toll-like receptor 2
• TLR4, toll-like receptor 4

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

We would like to thank A.R. Horswill for the green fluorescent protein (GFP) reporter, C.R. Nagler for the vector containing EGFP, J. Mecsas for Yersinia enterocolitica, and M. Raffatellu for Salmonella enterica serovar Typhimurium IR715 WT strain.

Funding

These studies were supported by NIH grants AI63426 and AI98973.