ORAL IMMUNIZATION WITH ATTENUATED VACCINE STRAINS OF VIBRIO-CHOLERAE EXPRESSING A DODECAPEPTIDE REPEAT OF THE SERINE-RICH ENTAMOEBA-HISTOLYTICA PROTEIN FUSED TO THE CHOLERA-TOXIN-B SUBUNIT INDUCES SYSTEMIC ANDMUCOSAL ANTIAMEBIC AND ANTI-V-CHOLERAE ANTIBODY-RESPONSES IN MICE

Entamoeba histolytica is a significant cause of morbidity and mortalit y worldwide. The serine-rich E. histolytica protein (SREHP) is a surfa ce-expressed trophozoite protein that includes multiple hydrophilic ta ndem repeats. A purified fusion protein between the dodecapeptide repe at of SREHP and cholera toxin B subunit (CTB) has previously been show n to be immunogenic in mice after oral inoculation when cholera toxin is coadministered as an immunoadjuvant. We engineered a live attenuate d El Tor Vibrio cholerae vaccine strain, Peru2, to express the SREHP-1 2-CTB fusion protein to the supernatant from either a plasmid [Peru2 ( pETR5.1)] or from a chromosomal insertion (ETR3). Vector strains were administered orally to germfree mice that were subsequently housed und er nongermfree conditions; mice received one (day 0) or two (days 0 an d 14) inoculations. No immunoadjuvant or cholera holotoxin was adminis tered. Mice that received two inoculations of Peru2(pETR5.1) had the m ost pronounced antiamebic systemic and mucosal immunologic responses. Less marked, but significant, anti-SREHP serum immunoglobulin G antibo dy responses were also induced in mice that received either one or two oral inoculations of strain ETR3. Anti-V. cholerae responses were als o induced, as measured by the induction of serum vibriocidal antibodie s and by serum and mucosal anti-CTB antibody responses. These results suggest that V. cholerae vector strains can be successful delivery veh icles for the SREHP-12-CTB fusion protein, to induce mucosal and syste mic antiamebic and anti-V. cholerae immune responses. The magnitude of these responses is proportional to the amount of SREHP-12-CTB produce d by the vector strain.