Abstract
In previous studies we found that immunizing mice with a sonicate of Helicobacter felis and adjuvant cholera toxin (CT; 10 micrograms) protected the animals against challenge with viable H. felis. The aim of this study was to determine whether a low dose of CT or its nontoxic B subunit (CTB) was effective as an adjuvant in Helicobacter oral vaccines. Significant protection against viable H. felis challenge was achieved in the animals immunized with H. felis antigen plus the combination of 0.5 microgram of CT and 10 micrograms of CTB (96%), with H. felis antigen plus 0.5 microgram of CT (95%), and with H. felis antigen plus 10 micrograms of CTB (83%). No protective effect was found in the mice immunized with either H. felis antigen alone or adjuvant CTB and CT alone. Twenty-six percent of mice immunized with Helicobacter pylori antigen plus CT (10 micrograms) were protected against H. felis challenge, confirming the value of the model in predicting effects of immunization in humans. The observation that immunity can be induced with a nontoxic adjuvant CTB opens the way for human studies with H. pylori vaccines and is a further step along the road to effective strategies of prevention of gastroduodenal diseases of major world significance.