Induction of an enteric Ig-response against ovalbumin and stimulation of the response by cholera toxin and its B-subunit in mice.

We induced ovalbumin (OA)-specific antibody responses in the murine small intestine and quantitated the responses by counting ovalbumin-specific antibody-containing cells (OACC) in the intestinal lamina propria, and by measuring anti-OA Ig titers in intestinal secretions. OA is a "weak" mucosal antigen and we could only induce intestinal anti-OA responses by intraperitoneal, primary injection of OA in water-in-oil emulsion and a mucosal booster with OA. Double staining of OACC for OA- and isotype-specificity demonstrated that 95% of all mucosal (intestinal) OACC produced IgA, whereas 95% of all systemic (splenic) OACC produced IgG. The intestinal anti-OA response could be stimulated by addition of cholera toxin (CT) or cholera toxin B-subunit (CTB) during the mucosal booster immunization. The stimulatory effect of CT did not depend on covalent coupling of CT and OA, while the stimulatory effect of CTB required covalent coupling of CTB with OA. Mucosal (intraduodenal) application of OA as such does not prime for a mucosal and systemic OACC response but induces tolerance. We demonstrated that coupling of OA with CT or CTB could overcome the inability of mucosal application of OA to prime for a mucosal OACC response. Although CT proved to be much more effective than CTB in stimulation of mucosal immune responses and possibly in prevention of tolerance induction, our results indicate that CTB is a useful (and safer) alternative.