Mice Are Protected from Helicobacter pylori Infection by Nasal Immunization with Attenuated Salmonella typhimurium phoP c Expressing Urease A and B Subunits

Abstract

ABSTRACT Live Salmonella typhimurium phoP c bacteria were tested as mucosal vaccine vectors to deliver Helicobacter pylori antigens. The genes encoding the A and B subunits of H. pylori urease were introduced into S. typhimurium phoP c and expressed under the control of a constitutive tac promoter (tac- ureAB ) or a two-phase T7 expression system (cT7- ureAB ). Both recombinant Salmonella strains expressed the two urease subunits in vitro and were used to nasally immunize BALB/c mice. The plasmid carrying cT7- ureAB was stably inherited by bacteria growing or persisting in the spleen, lungs, mesenteric or cervical lymph nodes, and Peyer’s patches of immunized mice, while the plasmid carrying tac- ureAB was rapidly lost. Spleen and Peyer’s patch CD4 + lymphocytes from mice immunized with S. typhimurium phoP c cT7- ureAB proliferated in vitro in response to urease, whereas cells from mice given S. typhimurium phoP c alone did not. Splenic CD4 + cells from mice immunized with phoP c cT7- ureAB secreted gamma interferon and interleukin 10, while Peyer’s patch CD4 + cells did not secrete either cytokine. Specific H. pylori anti-urease immunoglobulin G1 (IgG1) and IgG2A antibodies were detected following immunization, confirming that both Th1- and Th2-type immune responses were generated by the live vaccine. Sixty percent of the mice (9 of 15) immunized with S. typhimurium phoP c cT7- ureAB were found to be resistant to infection by H. pylori , while all mice immunized with phoP c tac- ureAB (15 of 15) or phoP c (15 of 15) were infected. Our data demonstrate that H. pylori urease delivered nasally by using a vaccine strain of S. typhimurium can trigger Th1- and Th2-type responses and induce protective immunity against Helicobacter infection.