N-terminal Domain of the Spike Protein of Porcine Epidemic Diarrhea Virus as a New Candidate Molecule for a Mucosal Vaccine

Kim, Sae-Hae; Cho, Byeol-Hee; Lee, Kyung-Yeol; Jang, Yong-Suk

Oral delivery of Ag can induce Ag-specific secretory IgA generation in the mucosal lining of the body, including the gastrointestinal tract, salivary glands, and mammary glands (25) . Therefore, we assumed that oral administration of Ag would be a suitable strategy to induce protective immunity against PEDV infection. However, a currently licensed oral mucosal subunit vaccine does not exist due to the lack of a mucosal adjuvant that can potentiate delivery of the Ag into M cells and enhance the immune response. In that sense, Ag, which is capable of targeting the Ag itself to M cells, is an attractive target for developing an oral mucosal vaccine against PEDV infection. For example, when fed orally, the rice-based cholera vaccine MucoRice-cholera toxin B subunit was taken up by M cells as a result of its M cell-targeting ability and efficiently induced cholera toxin B subunit-specific immune responses in both the systemic and mucosal compartments (26) . Therefore, our finding that the NTD 231-501 of the PEDV S protein specifically targets itself to M cells suggests that NTD 231-501 is a promising Ag candidate for an oral mucosal vaccine against PEDV infection. More importantly, the Ag-specific IgG2a isotype, which was efficiently induced by oral administration of NTD 231-501 , is closely related to the induction of protective immunity against a number of viruses, including influenza virus, Ebola virus, and yellow fever virus (1, 12, 27) . In addition, the Fc region of IgG2a activates Fc receptors with a high affinity by interacting with complement components, resulting in efficient induction of Fc receptor-mediated effector functions, such as Ab-dependent cell-mediated cytotoxicity and opsonophagocytosis by macrophages (28) . Moreover, IgG2a production is closely associated with the induction of Th1-type immune responses (21) . Consequently, we believe that Ag-specific IgG2a induction by oral administration of NTD 231-501 of the PEDV S protein is a promising strategy to develop an oral mucosal vaccine against PEDV infection.