The lost friend: H. Pylori

The Gram-negative bacterium Helicobacter pylori is predominantly known for its pathogenic role inducing peptic ulcer disease and gastric cancer. However, a considerable number of reports have linked H. pylori infection with the development of as well as protection from extra-gastrointestinal immunological disorders. Thus, recent epidemiological and experimental studies suggest that chronic infection with H. pylori might be beneficial for the host by conferring protection against allergic and chronic autoimmune diseases. In this chapter, we focus on the proposed beneficial role of H. pylori on atopic diseases, specifically asthma. We summarize the epidemiological data that support or refute a possible inverse correlation of H. pylori infection with atopic diseases. Experimental mouse studies show that asthma fails to develop in the presence of H. pylori. We examined and discussed involved bacterial factors and proposed mechanisms for this phenomenon. Mechanistically, the proposed mechanism involved in asthma protection is the particular property of H. pylori to induce regulatory T-cells (Tregs) with highly suppressive activity. These cells not only allow the bacterium to persist for decades in infected individuals but at the same time also work outside the stomach and confer protection against several diseases such as asthma and auto-inflammatory diseases.