M cells expressing the complement C5a receptor are efficient targets for mucosal vaccine delivery

Abstract

In the mucosal immune system, M cells are known as specialized epithelial cells that take up luminal antigens, although the receptors on M cells and the mechanism of antigen uptake into M cells are not well-understood. Here, we report the expression of the complement C5a receptor (C5aR) on the apical surface of M cells. C5ar mRNA expression in co-cultured Caco-2 human M-like cells was six-fold higher than in mono-cultured cells. C5aR expression was detected together with glycoprotein 2, an M-cell-specific protein, on the apical surface of M-like cells and mouse Peyer's patch M cells. Interestingly, after oral administration of Yersinia enterocolitica which expresses outer membrane protein H (OmpH) that is homologous to the Skp a1 domain of Escherichia coli, a ligand of C5aR, dense clustering and phosphorylation of C5aR were detected in M cells. Finally, targeted antigen delivery to M cells using C5aR as a receptor was achieved using the OmpH a1 of Y. enterocolitica such that the induction of ligand-conjugated antigen-specific immune responses was confirmed in mice after oral immunization of the OmpH b1a1-conjugated antigen. Collectively, we identified C5aR expression on M cells and suggest that C5aR could be used as a target receptor for mucosal antigen delivery. IntroductionThe mucosa are a primary target for infection and, at the same time, the first line of defense against many pathogens in which secretory IgA is a main protective component of the immune system [1]. In order to achieve an effective induction of antigenspecific immune responses using the oral route, obstacles such as oral tolerance induction and inefficient antigen delivery to the mucosal immune induction site should be resolved [2]. One of the most effective ways to overcome these obstacles is to target antigens to M cells, which are a primary gateway for the delivery of antigens from the intestinal lumen to the mucosal lymphoid organs. In addition, M cells have high transcytotic capacity and have highly distributed APCs in their basolateral pockets [3]. [5][6][7]. Therefore, identification of target receptors on M cells that could be used for successful mucosal vaccine delivery is one of the most interesting subjects in mucosal immunology. The complement and TLR systems are central components of the innate immune system, necessary for rapid responses to external dangers. However, in comparison to the well-recorded expression of TLR1, 2, and 4 and C-C chemokine receptor 5 in the M cell, expression of the molecules associated with the complement system has not yet been reported, despite possible roles for these proteins in activities such as homeostatic regulation of the mucosa by the induction of chemotactic and pro-inflammatory cytokines or antigen uptake through crosstalk with TLRs [8]. Among the molecules associated with the complement system, the complement C5a receptor (C5aR/CD88) was traditionally thought to exist only on myeloid cells. However, C5aR expression was recently verified on non-myeloid cells, including bronchial epithelial...

Targeted Delivery of VP1 Antigen of Foot-and-mouth Disease Virus to M Cells Enhances the Antigen-specific Systemic and Mucosal Immune Response

“…For example, M cell-specific antibody effectively delivers the conjugated antigen into the M cells, and UEA-1 interacting with α-L-fucose on M cells is used as a delivery mediator (13). Our previous studies also suggested that M cell-targeting ligand Co1 interacts with C5aR expressed on M cells and that this interaction is related with antigen delivery and induction of antigen-specific immune response (9,10). Our study also showed that Co1-conjugated viral antigen VP1 of FMDV more effectively interacted with M cells in ileal PPs compared to VP1 alone without Co1 ligand conjugation (Fig.…”

Antimicrobial peptide LL‐37 promotes antigen‐specific immune responses in mice by enhancing Th17‐skewed mucosal and systemic immunities

“…For example, GP2, an M-cell-specific protein expressed in both human and mouse M cells, plays a receptor role by aiding the uptake of FimH + bacteria into M cells [22]. In our previous study, we showed that complement 5a receptor could function as an M-cell-targeting receptor to induce Ag-specific immune responses in mucosal and systemic compartments [23]. In this study, we suggest the role of mFPR-2 as an M-cell-targeting receptor of LL-37-conjugated Ag.…”

Antigen targeting to M cells for enhancing the efficacy of mucosal vaccines

“…For example, the M cell-targeting ligand Co1 was selected by biopanning a phage display library against human M-like cells, suggesting the expression of a complement 5a receptor (C5aR) on M cells that was confirmed in mouse M cells. 59, 72 Transcriptomic profiling studies also suggest that genes for glycoprotein-2 ( Gp2 ), tumor necrosis factor-α expressed-induced protein 2 ( Tnfaip2 ) and Ccl9 are expressed in mature M cells. 73, 74 In addition, recent research progress on M cells suggested three pathways for luminal antigen sampling by M cells; nonspecific endocytosis, specific receptor-mediated endocytosis and via extension of transcellular dendritic processes by Lyso DCs, which have strong phagocytic activity and antigen sampling ability (Figure 3).…”

“…61 Similarly, the infection of Y. enterocolitica is closely related with C5aR on M cells, whereas the infection of Brucella abortus depends on a cellular prion protein on M cells. 59, 67 Based on these observations, it is plausible to use M cell-specific surface markers and receptors for the effective delivery of vaccine materials into the host. For example, when the M cell-specific antibody NKM 16-2-4, which recognizes α (1, 2) fucose-containing carbohydrates, was applied to an oral vaccine model against botulinum toxin, the NKM 16-2-4 combined antigen targeted M cells with high efficiency and induced antigen-specific IgA.…”