Anti-cholera toxin IgA-, IgG- and IgM-secreting cells in various rat lymphoid tissues after repeated intestinal or parenteral immunizations

Characterization and utility of two monoclonal antibodies to cholera toxin B subunit

Cholera toxin B subunit (CTB) is a potent immunomodulator exploitable in mucosal vaccine and immunotherapeutic development. To aid in the characterization of pleiotropic biological functions of CTB and its variants, we generated a panel of anti-CTB monoclonal antibodies (mAbs). By ELISA and surface plasmon resonance, two mAbs, 7A12B3 and 9F9C7, were analyzed for their binding affinities to cholera holotoxin (CTX), CTB, and EPICERTIN: a recombinant CTB variant possessing mucosal healing activity. Both 7A12B3 and 9F9C7 bound efficiently to CTX, CTB, and EPICERTIN with equilibrium dissociation constants at low to sub-nanomolar concentrations but bound weakly, if at all, to Escherichia coli heat-labile enterotoxin B subunit. In a cyclic adenosine monophosphate assay using Caco2 human colon epithelial cells, the 7A12B3 mAb was found to be a potent inhibitor of CTX, whereas 9F9C7 had relatively weak inhibitory activity. Meanwhile, the 9F9C7 mAb effectively detected CTB and EPICERTIN bound to the surface of Caco2 cells and mouse spleen leukocytes by flow cytometry. Using 9F9C7 in immunohistochemistry, we confirmed the preferential localization of EPICERTIN in colon crypts following oral administration of the protein in mice. Collectively, these mAbs provide valuable tools to investigate the biological functions and preclinical development of CTB variants.

Helper Th1 and Th2 cell responses following mucosal or systemic immunization with cholera toxin

We have used the potent mucosal immunogen cholera toxin (CT) to assess antigen-specific CD4+ T-cell responses, including Th1- and Th2-type cells in mucosa-associated tissues, e.g. Peyer's patches (PP), and systemic tissue, e.g. spleen (SP), for their regulatory role in the induction of CT-specific B-cell antibody responses in the gastrointestinal (GI) tract as well as in systemic sites. The CT was given by either oral or intravenous (i.v.) routes and the mice orally immunized with CT exhibited brisk IgA anti-CT antibody responses in faecal extracts and elevated IgG anti-CT antibody responses in serum. Further, significant IgA anti-CT spot-forming cells (SFCs) were seen in lamina propria lymphocytes (LPLs) from mice orally immunized with CT. In contrast, i.v. immunization with CT induced IgM and IgG anti-CT SFC responses in SP, and serum anti-CT antibodies of these two isotypes; no anti-CT responses were induced in the GI tract after immunization by this route. The CD4+ T cells isolated from PP and SP of mice orally immunized with CT were stimulated in vitro with CT-B-coated latex microspheres for 1-6 days, and the induction of IL-2 and interferon gamma (IFN-gamma) (Th1-type) or IL-4 and IL-5 (Th2-type) producing SFCs were analysed by a cytokine-specific ELISPOT and cytokine-specific mRNA was detected by reverse transcriptase (RT)-PCR assays.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of systemic and mucosal priming for mucosal immune responses to a bacterial protein antigen given with or coupled to cholera toxin (CT) B subunit, and effects of pre-existing anti-CT immunity

Intraperitoneal immunization with a bacterial protein antigen conjugated to cholera toxin B subunit (CTB) was generally less effective than intragastric or intranasal immunization in generating mucosal IgA antibodies, and in priming the mucosal immune system to respond to intragastric or intranasal boosting. Previous intragastric or intranasal immunization which generated high levels of mucosal and circulating antibodies to CTB did not suppress mucosal IgA responses induced by intragastric or intranasal immunization with bacterial antigen conjugated to or mixed with CTB, but serum antibody responses were inhibited depending on the route of immunization and whether CTB was conjugated to or mixed with the antigen.