Possible correlates of long-term protection against Helicobacter pylori following systemic or combinations of mucosal and systemic immunizations

The ability to induce long-term immunity to Helicobacter pylori is necessary for an effective vaccine. This study was designed to establish the most efficient route(s) (systemic, mucosal, or a combination) of immunization for induction of long-term immunity and to define correlates of protection. Mice were immunized orally alone (oral group), intramuscularly (i.m.) alone (i.m. group), orally followed by i.m. (oral/i.m. group), or i.m. followed by orally (i.m./oral group). Long-term protective immunity to oral H. pylori challenge was observed 3 months after immunization through the i.m. or oral/i.m. route. Protection correlated with an increase in H. pylori-specific interleukin-12 and both immunoglobulin G1 (IgG1) and IgG2a serum titers following challenge. Mice that were not protected (oral or i.m./oral) had increased levels of IgA in both sera and Peyer's patches. This study demonstrates the ability to induce long-term immunity against H. pylori, provides correlates of protection, and illustrates the crucial role of the immunization route(s).