SLAS Discovery Serum IgG fecalIgA 客宗 1 EGFP Gb-1 Gb-2 Gb-3 EGFP Gb-1 Gb-2 Gb-3 Figure 2. Enhanced green fluorescent protein(EGFP)-specific Serum IgG1 Serum IgG2a mucosal and systemic immune responses in orally immunized mice. Level of EGFP-specific immune esponse in mice orally immunized evaluated 5 days after the last munosorbent assay(ELISA).(A) and(D)IgG2a. Results are expresse as the reciprocal of the geometric n log2 titer and are the mean t EGFP Gb-1 Gb-2 Gb-3 EGFP Gb-1 Gb-2 Gb-3 and pp <0.00I indicate significant differences between the value compared secretion in splenocytes restimulated with EGFPs. IL-4 membrane of intestinal epithelial cells is a major limitation level was significantly raised in the Gb-l-immunized group to be overcome for the successful development of an oral compared to the eGFP group(Fig 3A). Since IgGl produc- vaccine. In the case of subunit vaccines, denaturation tion and IL-4 secretion are indicators of Th2-type response, caused by the acidic environment of the stomach is also a this implies that oral immunization with Gb-1 ligand barrier to oral vaccines. Encapsulation of vaccines in induces predominantly Th2-type immunity against the sub- nano- and microparticulate forms such as polylactide Ject antigen (PLA), polylactide-coglycolide(PLga), or liposomes, and the use of enteric-coated capsules may offer some protec Discussion tion against acidic and enzymatic degradatic ever, these strategies have affected the delivery of vaccines Oral vaccination induces not only antibody response in the across intestinal epithelial cells ystemic compartment, but also the serum IgG response is One approach to enhance drug and particulate delivery sys- strengthened by IgA production at the mucosal surface. tems across the intestinal epithelial barrier is to target Ags to This makes oral vaccination superior compared to systemic specific transcytotic ic receptor of the intestine. Cells are spe vaccination where only the IgG response is elicited. Low cialized cells that internalize luminal Ags across the epithelial cost and needle-free delivery are other attractive features of layer to the underlying immune induction sites without degra- mucosal/oral vaccination, so it is a feasible and economic dation and play an important role in initiating Ag-specific vaccination strategy, especially in developing countries. mucosal immune responses by inducing the production However, low permeability of vaccines across the plasma of secretory IgA. Therefore, the M-cell-mediated Ag6 SLAS Discovery secretion in splenocytes restimulated with EGFPs. IL-4 level was significantly raised in the Gb-1–immunized group compared to the EGFP group (Fig. 3A). Since IgG1 produc￾tion and IL-4 secretion are indicators of Th2-type response, this implies that oral immunization with Gb-1 ligand induces predominantly Th2-type immunity against the sub￾ject antigen. Discussion Oral vaccination induces not only antibody response in the systemic compartment, but also the serum IgG response is strengthened by IgA production at the mucosal surface.19,21 This makes oral vaccination superior compared to systemic vaccination where only the IgG response is elicited.22 Low cost and needle-free delivery are other attractive features of mucosal/oral vaccination,4 so it is a feasible and economic vaccination strategy, especially in developing countries. However, low permeability of vaccines across the plasma membrane of intestinal epithelial cells is a major limitation to be overcome for the successful development of an oral vaccine. In the case of subunit vaccines, denaturation caused by the acidic environment of the stomach is also a barrier to oral vaccines.23 Encapsulation of vaccines in nano- and microparticulate forms such as polylactide (PLA), polylactide-coglycolide (PLGA), or liposomes, and the use of enteric-coated capsules may offer some protec￾tion against acidic and enzymatic degradation24–29; how￾ever, these strategies have affected the delivery of vaccines across intestinal epithelial cells. One approach to enhance drug and particulate delivery sys￾tems across the intestinal epithelial barrier is to target Ags to specific transcytotic receptor of the intestine.23 M cells are spe￾cialized cells that internalize luminal Ags across the epithelial layer to the underlying immune induction sites without degra￾dation and play an important role in initiating Ag-specific mucosal immune responses by inducing the production of secretory IgA.2,30 Therefore, the M-cell–mediated Ag Figure 2. Enhanced green fluorescent protein (EGFP)–specific mucosal and systemic immune responses in orally immunized mice. Level of EGFP-specific immune response in mice orally immunized with the indicated antigens was evaluated 5 days after the last immunization by enzyme-linked immunosorbent assay (ELISA). (A) Serum IgG, (B) fecal IgA, (C) IgG1, and (D) IgG2a. Results are expressed as the reciprocal of the geometric mean log2 titer and are the mean ± SE of five mice per group. **p < 0.01 and ***p < 0.001 indicate significant differences between the values compared