There is evidence that Helicobacter pylori infection up-regulates the expression of HLA class II molecules by gastric epithelial cells (GEC). In this study we evaluated whether GEC are capable of expression of costimulatory molecules in H. pylori gastritis. The expression of FasL by GEC, before and after eradication of H. pylori, was also studied. Thirty patients (23 men) aged 27-81 years (53.67 +/- 13.99 years (mean +/- s.d.)) with dyspepsia were studied. Upper gastrointestinal endoscopy was performed and six biopsies were obtained (antrum, n = 3; corpus, n = 3) for Campylobacter-Like Organisms (CLO) test and histology; 23 (16 men) were H. pylori+ and seven (all men) were H. pylori- by both methods and served as controls. Helicobacter pylori eradication therapy was given to H. pylori+ patients and all patients were re-endoscoped after 116 +/- 9 days. Formalin-fixed paraffin-embedded tissue sections were stained by the ABC immunoalkaline phosphatase method. In H. pylori gastritis HLA-DR was expressed and correlated with disease activity (P < 0.01). No HLA-DR was observed in controls. In H. pylori-eradicated patients significant decrease of HLA-DR was found (antrum, P < 0. 001). ICAM-1 was expressed by GEC in 80% of H. pylori+ patients; ICAM-1 expression did not correlate with gastritis parameters and decreased significantly after eradication (antrum, P < 0.01). B7-1 and B7-2 were expressed on H. pylori+ samples and their expression decreased after eradication, albeit not significantly. Weak epithelial expression of both B7 molecules was observed in all the controls. FasL was steadily expressed by GEC in both H. pylori+ and H. pylori- patients and remained almost unchanged after eradication. These findings suggest that GEC may acquire antigen-presenting cell properties in H. pylori infection through de novo expression of HLA-DR and costimulatory molecules. This seems to be attenuated after eradication and resolution of mucosal inflammation. The same cells exhibit the capacity to control the inflammatory process, probably by inducing apoptotic cell death to Fas-bearing infiltrating lymphocytes.