RECOMBINANT ANTIGENS PREPARED FROM THE UREASE SUBUNITS OF HELICOBACTER SPP - EVIDENCE OF PROTECTION IN A MOUSE MODEL OF GASTRIC INFECTION

Urease is an important virulence factor for gastric Helicobacter spp. To elucidate the efficacy of individual urease subunits to act as muco sal immunogens, the genes encoding the respective urease subunits (Ure A 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 prote ins were purified by affinity and anion-exchange chromatography techni ques and had predicted molecular masses of approximately 68 and 103 kD a, respectively. Western blotting (immunoblotting) studies indicated t hat the urease components of the fusion proteins were strongly immunog enic and were specifically recognized by polyclonal rabbit anti-Helico bacter sp. sera. The fusion proteins (50 mu g) were used, in combinati on;with a mucosal adjuvant (cholera toxin), to orogastrically immunize mice against H. felis infection. Gastric tissues from H. felis-challe nged 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 he terologous 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 Heli cobacter infection.