Oral immunization against cholera toxin with a live Yersinia enterocolitica carrier in mice.

The 70-kb pYV plasmid of Yersinia enterocolitica directs the synthesis and secretion of several virulence determinants called Yops. These proteins are produced during the invasion of the host tissues and induce a strong antibody response. The yop genes are transcribed from strong promoters activated by a common transcription activator. Recombinant Y. enterocolitica strains expressing the B subunit of the cholera toxin were constructed from a yopH-ctxB operon fusion. Integration of the gene ctxB in the pYV plasmid itself, by a double crossing over, ensured its stability in the infecting bacteria. Oral inoculation of recombinant bacteria in mice elicited serum and intestinal antibody responses and resulted in protection of the immunized mice against a cholera toxin challenge. Secretory immunoglobulin A antibodies against the cholera toxin B subunit occurred not only in the intestines but also in the respiratory tract.