ctor. There was no T-cell proliferation response in the oral immunized groups. These results suggested that Yeast-GP5 could induce PRRSV-specific T-cell proliferation when delivered subcutaneously.

Effect of Yeast-GP5 on IL-4 expression in T cells
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Cytokines play a pivotal role in the modulation of immune responses. To develop cytokine profiles, we first examined the level of IL-4 (T~H~2 type) production in CD4^+^ T cells using a fluorescence activated cell sorter (FACS). As shown in [Fig. 4](#F4){ref-type="fig"}, there was no significant difference in the percentage of IL-4^+^CD4^+^ T cells between Yeast-GP5 and Yeast-vector, suggesting that immunization with Yeast-GP5 cannot efficiently stimulate T~H~2-type cytokine secretion.

Effect of Yeast-GP5 on IFN-γ production in T cells
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We also examined the levels of IFN-γ in CD4^+^ T cells and CD8^+^ T cells of splenocytes at day 7 after the third immunization. As shown in [Figs. 5A\~F](#F5){ref-type="fig"}, significantly higher percentages of PRRSV-specific CD4^+^IFN-γ^+^ T cells and CD8^+^IFN-γ^+^ T cells were detected in mice immunized with Yeast-GP5, both subcutaneously and orally. The expression levels of IFN-γ in CD4^+^ T cells and CD8^+^ T cells from mice vaccinated subcutaneously with Yeas-GP5 were 1.64- and 2.30-fold higher than those of the Yeast-vector group, respectively. For the oral immunization groups, the percentage of IFN-γ^+^CD4^+^ T cells and IFN-γ^+^CD8^+^ T cells were 2.95- and 4.0-fold higher than those of the control, respectively ([Figs. 5C and F](#F5){ref-type="fig"}). These results suggest that Yeast-GP5 can stimulate both PRRSV-specific T~H~1 and CD8^+^ effector cell responses.

Discussion
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Various studies have shown that yeast is a desirable candidate for use as a vaccine platform \[[@B2],[@B3]\]. For example, the nonpathogenic recombinant *S. cerevisiae* has been shown to stimulate both humoral and cell-mediated immune re