The mucosal immune system forms the largest part of the entire immune system, containing about three-quarters of all lymphocytes and producing grams of secretory IgA daily to protect the mucosal surface from pathogens1,2,3. To evoke the mucosal immune response, antigens on the mucosal surface must be transported across the epithelial barrier into organized lymphoid structures such as Peyer’s patches4. This function, called antigen transcytosis, is mediated by specialized epithelial M cells5,6. The molecular mechanisms promoting this antigen uptake, however, are largely unknown. Here we report that glycoprotein 2 (GP2), specifically expressed on the apical plasma membrane of M cells among enterocytes, serves as a transcytotic receptor for mucosal antigens. Recombinant GP2 protein selectively bound a subset of commensal and pathogenic enterobacteria, including Escherichia coli and Salmonella enterica serovar Typhimurium (S. Typhimurium), by recognizing FimH, a component of type I pili on the bacterial outer membrane. Consistently, these bacteria were colocalized with endogenous GP2 on the apical plasma membrane as well as in cytoplasmic vesicles in M cells. Moreover, deficiency of bacterial FimH or host GP2 led to defects in transcytosis of type-I-piliated bacteria through M cells, resulting in an attenuation of antigen-specific immune responses in Peyer’s patches. GP2 is therefore a previously unrecognized transcytotic receptor on M cells for type-I-piliated bacteria and is a prerequisite for the mucosal immune response to these bacteria. Given that M cells are considered a promising target for oral vaccination against various infectious diseases7,8, the GP2-dependent transcytotic pathway could provide a new target for the development of M-cell-targeted mucosal vaccines.
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We thank K. Kanno and A. Yamada for help in immunoelectron microscopy; Y. Yamada for secretarial assistance; M. Ohmae for technical assistance; H. Watarai for pertinent advice and discussion; P. D. Burrows, T. Takemori, S. Yamasaki and H. Kitamura for critical review of the manuscript; and the National BioResource Project (NIG, Japan) for E. coli (the Keio collection). This study was supported in part by Grants-in-Aid for Young Scientists (B) (K.H.), Scientific research (B) (H.O.), Scientific Research in Priority Areas (H.O. and K.H.), and Scientific Research on Innovative Areas (H.O.) from the Ministry of Education, Culture, Sports, Science and Technology of Japan, the Takeda Science Foundation (K.H.), and NIH awards DK56339 and DK43294 (A.W.L.).
Author Contributions K. Hase and K. Kawano designed and performed the experiments, analysed the data and wrote the manuscript. T.N., G.S.P., S.F., M.E., K. Kadokura, Y.F., S. Kawano, A.Y., G.N., S. Kimura, M.I., K. Hamura, S.W. and H.K. contributed to the experimental work, and T.M. helped in data analysis. T.T. developed the FimH-deficient strain of rSalmonella-ToxC. K.I. prepared bacteria. S-I.F. and A.W.L. provided GP2-deficient mice. H.O. supervised the project and made significant contributions to the manuscript.
This movie shows a three-dimensional image of M cells taking up anti-mouse GP2 mAb in the ligated intestinal loop assay (see file s1 for full Legend).
The movie shows the visualization of an M cell taking up E. coli (see file s1 for full Legend).
This movie shows the transcytosis of S. Typhimurium by an M cell (see file s1 for full Legend).
This movie shows the transport of E. coli from an M cell to underlying DC (see file s1 for full Legend).