Absence of CD4 + CD25 + regulatory T cells is associated with a loss of regulation leading to increased pathology in Helicobacter pylori ‐infected mice

SUMMARY Helicobacter pylori induces symptomatic chronic gastritis in a subpopulation of infected individuals. The mechanism(s) determining the development and severity of pathology leading to symptoms are not fully understood. In a mouse model of H. pylori infection we analysed the influence of immunoregulatory CD4 + CD25 + T cells on H. pylori colonization and gastritis. Athymic C57BL/6  nu/nu mice were reconstituted with (a) lymph node (LN) cells (b) LN cells depleted of CD25 + T cells (CD25 – LN) or (c) not reconstituted at all. Mice were then infected orally with 3 × 10 8 H. pylori SS1 bacteria. At 2 and 6 weeks after the inoculation there was a significant ( P  < 0·001) reduction in H. pylori colonization in athymic mice transferred with CD25 – LN cells compared to mice transferred with LN cells. Colonization was still reduced at 12 weeks after inoculation. Mice transferred with CD25 – LN cells showed an earlier onset and increased severity of gastritis as compared to mice receiving LN cells. Splenic cells isolated from mice receiving CD25 – LN cells produced the highest level of IFN‐ γ on stimulation with H. pylori antigens in vitro, had a higher H. pylori ‐specific DTH response and increased infiltration of CD4 + T cells and macrophages in the gastric mucosa. Athymic mice not transferred with T cells had persistent high H. pylori colonization and displayed a normal gastric epithelium without inflammatory cells. In conclusion, CD4 + CD25 + cells reduce immunopathology in H. pylori infection, possibly by reducing the activation of IFN‐ γ producing CD4 + T cells, even at the expense of a higher H. pylori load in the gastric mucosa.