title: An enzymatically active a domain is required for cholera-like enterotoxins to induce a long-lived blockade on the induction of oral tolerance: new method for screening mucosal adjuvants.
abstract: The cholera-like enterotoxins (CLETS), cholera toxin (CT) and Escherichia coli heat-labile toxin (LT), are powerful mucosal adjuvants. Here we show that these toxins also induce a long-lived blockade (of at least 6 months) on the induction of oral tolerance when they are coadministered with the antigen ovalbumin. Strikingly, only enzymatically active CLETS induced this blockade on the induction of oral tolerance. In this regard, the enzymatically inactive mutants of CT and LT, CTK63 and LTK63, and their recombinant B pentamers, rCTB and rLTB, failed to block the induction of oral tolerance, demonstrating a stringent requirement for an enzymatically active A domain in this phenomenon. Together with the results of other recent studies, these results indicate that the enzymatic activity of CLETS, most likely cyclic AMP elevation, is responsible for their adjuvant effects. The results of this study also indicate that measuring the ability of putative mucosal adjuvants to block the induction of oral tolerance may be a superior method for measuring mucosal adjuvanticity.
authors.affiliation: Division of Vaccine Research, Institute of Human Virology, University of Maryland Biotechnology Institute, Baltimore 21201, USA.
authors.forename: Kenneth C
authors.initials: KC
authors.lastname: Bagley
authors.forename: Sayed F
authors.initials: SF
authors.lastname: Abdelwahab
authors.forename: Robert G
authors.initials: RG
authors.lastname: Tuskan
authors.forename: George K
authors.initials: GK
authors.lastname: Lewis
mesh_terms: D000276:Adjuvants, Immunologic; D000284:Administration, Oral; D000818:Animals; D001427:Bacterial Toxins / Q000008:administration & dosage / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D002772:Cholera Toxin / Q000008:administration & dosage / Q000737:chemistry* / Q000235:genetics / Q000276:immunology*; D004768:Enterotoxins / Q000008:administration & dosage / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D029968:Escherichia coli Proteins; D007108:Immune Tolerance; D018928:Immunity, Mucosal; D007114:Immunization; D007115:Immunization Schedule; D051379:Mice; D008807:Mice, Inbred BALB C; D009154:Mutation; D010047:Ovalbumin / Q000008:administration & dosage / Q000276:immunology
chemical_list: D000276:Adjuvants, Immunologic; D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D010047:Ovalbumin; D002772:Cholera Toxin; C027538:heat-labile enterotoxin, E coli