[Study on adjuvant effect of oral recombinant subunit vaccine formulated with chitosan against human enterovirus 71].
To evaluate the adjuvant effect of recombinant enterovirus 71 (EV71) subunit vaccine formulated with chitosan, rabbits were orally immunized with recombinant VP1 (rVP1) or rVP1 mixed with chitosan adjuvant. Levels of virus-specific IgG and IgA antibodies in sera, mucosal wash buffer (intestine, nasal cavity, and lung), and feces were determined by indirect enzyme-linked immunosorbent assay (ELISA). The titers of neutralizing antibodies against EV71 were determined using cytopathic effect-based neutralizing assay, and levels of cytokines (IFN-gamma and IL-4) secreted from in vitro-cultured rabbit splenic lymphocytes under antigen stimulation were also determined by ELISA. Results showed that immunization with rVP1 alone could only induce low levels of serum IgG and mucosal IgA, while rVP1 combined with chitosan adjuvant were able to induce significantly higher levels of antibodies, rVP1 can only induce neutralizing antibodies when used in combination with chitosan. Levels of IFN-gamma and IL-4 in the group immunized with rVP1 plus chitosan were significantly higher than those in the group immunized with rVP1 only or those in the control groups. Our study lays the foundation for development of oral VP1 vaccine against EV71 infection.