The bacterium Helicobacter pylori lives in the gastric mucus layer of humans and induces a chronic inflammatory response that can result in both peptic ulceration and gastric neoplasms. Helicobacter pylori infection can be considered as a 'slow', adaptive and autoregulating process. The mechanisms by which this slow bacterial pathogen survives and interacts with the host immune system may provide a model for other persistent mucosal pathogens.