BACKGROUND AND AIMS Helicobacter pylori is a major cause of peptic ulcers and gastric cancer. Vaccine development is progressing but there is concern that immunisation may exacerbate Helicobacterinduced gastritis: prophylactic immunisation followed by challenge withH felis or H pylori can induce a more severe gastritis in mice than seen with infection alone. The aim of this study was to investigate the relationship between immunity toHelicobacter infection and post-immunisation gastritis.

RESULTS Prophylactic immunisation induced a reduction in bacterial colonisation followingH felis challenge which was associated with increased severity of active gastritis with neutrophil infiltration and atrophy. However, immunised mice challenged with H pylori SS1 had little evidence of pathology. Long term follow up showed that post-immunisation gastritis was evident at three months. However, from six months onwards, although immunised/challenged mice still developed gastritis, there was no significant difference between inflammation in these mice and infected controls. Post-immunisation gastritis was not associated with the serum antibody response. Immunisation prevented the formation of secondary lymphoid aggregates in the gastric tissue.

CONCLUSION TheH felis mouse model of post-immunisation gastritis is the most extreme example of this type of pathology. We have shown in this model that post-immunisation gastritis is a transient event which does not produce long term exacerbation of pathology.