Serum-derived IgG1-mediated immune exclusion as a mechanism of protection against H. pylori infection.

The induction of protective immunity against Helicobacter challenge in a murine model was found to correlate with the magnitude of IgG (serum and gastric lavage) responsiveness to intra-nasal (i.n.) immunisation. IgG1-secreting hybridoma backpacks in Helicobacter pylori (H. pylori)-infected mice revealed serum transudation into the stomach. A Lpp20-specific monoclonal antibody was associated with significantly reduced H. pylori colonisation. Histology revealed aggregates of the remaining H. pylori in these mice, suggesting a role for IgG1-mediated immune exclusion of the bacteria. In vitro immunogold electron microscopy supported this hypothesis, but also suggested that a threshold of H. pylori-specific antibody needs to be maintained if immune exclusion by the host is to overcome immune evasion by the bacteria.