Fig. 5.

Induction of protective immunity against CT by rice-expressed CTB. (A) The neutralizing index calculated with OD₄₅₀ obtained by GM1-ELISA. The serum of mice immunized with rice-expressed CTB or purified rCTB, but not with nontransgenic rice or PBS, completely blocked the binding of CT to coated GM1-ganglioside. ∗∗, P < 0.01, CTB rice or rCTB vs. PBS. (B) The elongation assay with CHO cells revealed a morphology similar to normal cells (1) when the cells were stimulated with CT pretreated with serum from mice immunized with rice-expressed CTB (2) or purified rCTB (3), but a marked elongation when stimulated by CT pretreated with the serum from mice immunized with nontransgenic rice, PBS, or nontreated CT (4) as shown by the arrows. (C) In contrast to mice receiving WT rice or PBS, mice orally vaccinated with rice-expressed CTB showed no symptoms of diarrhea and a low level of intestinal water. ∗, P < 0.05, CTB rice or rCTB vs. PBS.