Urease is an important
virulence factor for gastric Helicobacter spp. To elucidate the efficacy of individual
urease subunits to act as mucosal immunogens, the genes encoding the respective
urease subunits (
UreA and UreB) of Helicobacter pylori and Helicobacter felis were cloned in an expression vector (pMAL) and expressed in Escherichia coli cells as translational fusion
proteins. The recombinant
UreA and UreB
proteins were purified by affinity and
anion-exchange chromatography techniques and had predicted molecular masses of approximately 68 and 103 kDa, respectively. Western blotting (immunoblotting) studies indicated that the
urease components of the fusion
proteins were strongly immunogenic and were specifically recognized by polyclonal rabbit anti-Helicobacter sp. sera. The fusion
proteins (50 micrograms) were used, in combination with a mucosal adjuvant (
cholera toxin), to orogastrically immunize mice against H. felis
infection. Gastric tissues from H. felis-challenged mice were assessed by the biopsy
urease test and by histology. In mice immunized with recombinant H. felis UreB, 60% of animals (n = 7) were histologically negative for H. felis bacteria after challenge
at 17 weeks. This compared with 25% (n = 8) for mice immunized with the heterologous H. pylori UreB
antigen. Neither the homologous nor the heterologous
UreA subunit elicited protective responses against H. felis
infection in mice. The study demonstrated that a recombinant subunit
antigen could induce an immunoprotective response against gastric
Helicobacter infection.