Oral immunization of mice with Saccharomyces cerevisiae expressing a neutralizing epitope of ApxIIA exotoxin from Actinobacillus pleuropneumoniae induces systemic and mucosal immune responses.

An oral delivery system based on ApxIIA#5-expressed on Saccharomyces cerevisiae was studied for its potential to induce immune responses in mice. Murine bone marrow-derived dendritic cells (DCs) stimulated in vitro with ApxIIA#5-expressed on S. cerevisiae upregulated the expression of maturation and activation markers, leading to production of tumor necrosis factor-α, interleukin (IL)-1β, IL-12p70 and IL-10. Presentation of these activated DCs to cluster of differentiation CD4+ T cells collected from mice that had been orally immunized with the ApxIIA#5-expressed on S. cerevisiae elicited specific T-cell proliferation. In addition, the orally immunized mice had stronger antigen-specific serum IgG and IgA antibody responses and larger numbers of antigen-specific IgG and IgA antibody-secreting cells in their spleens, Peyer's patches and lamina propria than did those immunized with vector-only S. cerevisiae or those not immunized. Furthermore, oral immunization induced T helper 1-type immune responses mediated via increased serum concentrations of IgG2a and an increase predominantly of IFN-γ-producing cells in their spleens and lamina propria. Our findings suggest that surface-displayed ApxIIA#5-expressed on S. cerevisiae may be a promising candidate for an oral vaccine delivery system for eliciting systemic and mucosal immunity.