MUCOSAL IMMUNIZATION WITH A BACTERIAL PROTEIN ANTIGEN GENETICALLY COUPLED TO CHOLERA-TOXIN A2 B SUBUNITS/

The generation of secretory IgA Abs for specific immune protection of mucosal surfaces depends on stimulation of the mucosal immune system, but this is not effectively achieved by parenteral or even oral admini stration of most soluble Ags. To harness the exceptional mucosal immun ogenicity of cholera toxin (CT), which is largely attributed to the ce ll-binding property of its B subunit, for the generation of other oral vaccines, we have genetically replaced the toxic Al subunit of CT wit h a 42-kDa segment of a streptococcal protein adhesin. This construct was expressed in Escherichia coli as a chimeric protein that retained the G(M1) ganglioside-binding activity of CT subunit B and the antigen icity of the streptococcal adhesin, as shown by G(M1)-ELISA developed with Abs to the streptococcal segment. The protein composition of chro matographically purified chimeric protein was verified by SDS-PAGE and Western blotting with Abs to both antigenic components of the constru ct. Peroral administration of this chimeric immunogen in mice elicited high levels of mucosal IgA and serum Ige Abs to the streptococcal adh esin, which persisted for at least 6 mo. This strategy allows the deve lopment of similar constructs from other candidate Ags for oral immuni zation against a variety of mucosally acquired infections.