Protection against ExperimentalHelicobacter pyloriInfection after Immunization with InactivatedH. pyloriWhole-Cell Vaccines

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Abstract
The protective effect of therapeutic oral immunization with homologous and heterologous formalin-inactivatedHelicobacter pyloricells given together with cholera toxin as an adjuvant was evaluated with C57BL/6 mice infected withH. pyloriSydney strain 1 (SS1). The bacteria used for immunization were strains that were either homologous or heterologous with regard to the O antigen (i.e., the Lewis antigen [Le antigen]) expressed by the lipopolysaccharide of the infectingH. pyloriSS1 strain. We found that repeated oral immunization with inactivatedH. pyloriSS1 cells can significantly inhibit an existing infection (P< 0.001) and that the protection induced by such therapeutic immunization extends to protection against reinfection (P< 0.001). A similar level of protection was also achieved by immunization with another inactivatedH. pyloristrain having the same O antigen (Le antigen) as the infectingH. pyloriSS1 strain. In contrast, immunization with inactivated strains expressing a heterologous O antigen, Lex, provided less protection or no protection. Immunization withH. pylorilysate preparations, on the other hand, resulted in significant comparable protection whether the lysates were prepared from an Lexstrain or an Leystrain. Postimmunization gastritis was seen in mice that were protected after vaccination but not in unimmunized or unprotected mice. In conclusion, therapeutic immunization with inactivatedH. pyloriwhole-cell vaccines may provide strong protection both against experimentalH. pyloriinfection and against later reinfection.