AIM: To analyze the level of apoptosis in different mucosal compartments and the differential expression of Fas/Fas-ligand and perforin in H pylori-associated gastric ulcer.METHODS: Antral specimens from patients withH pylori-related active gastric ulcer (GU),H pylori-related gastritis, and non-infected controls were analysed for densities and distribution of apoptotic cells determined by the TdT-mediated dUDP-biotin nick-end-labelling method. GU patients were submitted to eradication therapy with follow-up biopsy after 60 d. Fas, FasL, and perforin-expressing cells were assessed by immunoperoxidase, and with anti-CD3, anti-CD20 and anti-CD68 by double immunofluorescence and confocal microscopy.Quantitative analysis was performed using a computerassisted image analyser.RESULTS: H pylori-infected antrum showed greater surface epithelial apoptosis which decreased after eradication therapy. In the lamina propria, higher rates of mononuclear cell apoptosis were observed in H pylorigastritis. Co-expression of Fas with T-cell and macrophage markers was reduced in GU. FasL- and perforinexpressing cells were increased in H pylori-infection and correlated with epithelial apoptosis. Perforin-expressing cells were also increased in GU compared with H pylorigastritis.CONCLUSION: Epithelial apoptosis is increased in H pylori-infection and correlates to FasL- and perforinexpression by T cells. Expression of perforin is correlated with the tissue damage, and may represent the enhancement of a distinct cytotoxic pathway in GU. Increased expression of FasL not paralleled by Fas on T-cells and macrophages may indicate a reduced susceptibility to the Fas/FasL-mediated apoptosis of lymphoid cells in H pylori-infection.