Induction of rat secretory IgA antibodies against cholera toxin by a synthetic peptide.

There is accumulating evidence concerning the possible importance of secretory IgA antibodies in defence mechanisms against infections of the gastrointestinal tract, including cholera. Intestinal IgA antibodies are also thought to play a major role in protection against the diarrhoeogenic effects of cholera toxin. We therefore attempted to induce secretory IgA antibodies towards a reactive synthetic peptide from the cholera toxin B subunit sequence. We report that rat biliary secretory IgA antibodies against the CTP3 peptide (residues 50-64 of the B subunit) were obtained by three intra-Peyer's patch immunizations, at 2-week intervals, with CTP3 conjugated to tetanus toxoid in complete Freund's adjuvant. Purified secretory IgA fractions from bile of such immunized rats reacted with the carrier toxoid, but also with the CTP3 peptide, and with the native cholera toxin, they also partially neutralized its biological activity, as assayed by inhibition of in vitro cholera toxin-induced cAMP production in mouse thymocytes.