Interleukin-15 enhance DNA vaccine elicited mucosal and systemic immunity against foot and mouth disease virus

Aerosol transmission of foot and mouth disease virus (FMDV) is believed to be an important route of infection. Induction of mucosal response is thought to be effective way against such infection. Various approaches have been developed including the use of molecules adjuvant and polymers delivery for the mucosal delivery of DNA vaccine. In this study, using low molecular weight chitosan as a delivery vehicle, we investigated whether co-administration intranasally of the FMDV DNA vaccine, pcD-VP1 and a construct expressing IL-15 as the molecular adjuvant can enhance mucosal and systemic immune responses in animals. Compared to the group intranasally immunized with pcD-VP1 alone, the group immunized with the molecular adjuvant not only was induced higher level of mucosal sIgA but also serum IgG. Interestingly, intranasal delivery of the IL-15 construct with pcD-VP1 significantly enhanced the cell-mediated immunity (CMI) compared to the pcD-VP1 alone, as evidenced by the higher level of antigen-specific T-cell proliferation, cytotoxic T lymphocyte (CTL) response and higher expressions of IFN-γ in both CD4+ and CD8+ T cells inform the spleen and mucosal sites. Consistently, IL-15 as adjuvant provided higher level of FMDV neutralizing antibody against FMDV and high secretions of IgA producing cells in mucosal tissues. Taken together, the results demonstrated that intranasal delivery of IL-15 as a mucosal adjuvant can enhance the antigen-specific mucosal and systemic immune responses, which may provide a protection against the FMDV initial infection.