Background:  Although previous studies have reported important roles of CD4⁺ type1‐helper T cells and regulatory T cells in Helicobacter‐associated gastritis, the significance of CD8⁺ cytotoxic T cells remains unknown. To study the roles of CD8⁺ T cells, we examined the immune response in the gastric mucosa of Helicobacter felis‐infected major histocompatibility complex (MHC) class II‐deficient (II^−/–) mice, which lack CD4⁺ T cells.

Materials and methods:  Stomachs from H. felis‐infected wild‐type and infected MHC II^−/– mice were examined histologically and immunohistochemically. Gastric acidity and serum levels of anti‐H. felis antibodies were measured. The expression of pro‐inflammatory and anti‐inflammatory cytokine, Fas‐ligand, perforin, and Foxp3 genes in the gastric mucosa was investigated.

Results:  H. felis‐infected MHC II^−/– mice developed severe gastritis, accompanied by marked infiltration of CD8⁺ cells. At 1 and 2 months after inoculation, mucosal inflammation and atrophy were more severe in MHC II^−/– mice, although gastritis had reached similar advanced stages at 3 months after inoculation. There was little infiltration of CD4⁺ cells, and no Foxp3‐positive cells were detected in the gastric mucosa of the infected MHC II^−/– mice. The expression of the interleukin‐1β and Fas‐ligand genes was up regulated, but that of Foxp3 was down regulated in the infected MHC II^−/– mice. Serum levels of anti‐H. felis antibodies were lower in the infected MHC II^−/– mice, despite severe gastritis.

Conclusions:  The present study suggests that cross‐primed CD8⁺ cytotoxic T cells can induce severe H.‐associated gastritis in the absence of CD4⁺ helper T cells and that Foxp3‐positive cells may have an important role in the control of gastric inflammation.