Effects of oral vaccination and immunomodulation by cholera toxin on experimental Helicobacter pylori infection, reinfection, and gastritis.

Therapeutic vaccination is an attractive strategy to control infection and disease caused by Helicobacter pylori. In mice infected with H. pylori we have studied the protective effect of oral immunization with an H. pylori lysate preparation given together with the mucosal adjuvant cholera toxin (CT), both against the initial infection and against a later reinfection challenge. We have also examined the effects of treatment with the CT adjuvant alone on H. pylori infection and reinfection. Specific immunization with lysate was found to result in a sixfold reduction of the extent (bacterial load) of the primary infection and also to provide similar levels of protection against reinfection. However, these effects were associated with severe postimmunization gastritis. In contrast, oral treatment with CT alone at the time of initial infection, while unable to suppress the initial infection, gave rise to a 20-fold reduction in bacterial load upon reinfection without causing any associated gastric inflammation. Both the infected animals that were specifically immunized and those that were treated with CT only displayed increased in vitro proliferative responses of mononuclear cells to H. pylori antigens. Antibody levels in response to H. pylori were on the other hand only marginally increased after treatment with CT, whereas they were markedly elevated after immunization with lysate plus CT, with a rise in both (Th2-driven) immunoglobulin G1 (IgG1) and, especially, (Th1-driven) IgG2a antibodies. The results illustrate the complex balance between protection and harmful inflammation after postinfection vaccination against H. pylori as studied in a mouse model.