[Helicobacter pylori infection and allergic diseases]

The prevalence of airway allergic diseases has increased in developed countries including Japan. There is a much published potential link between allergy and childhood infection. In 1989, Strachan proposed "hygiene hypothesis" that infections and living in an unhygienic environment might prime the immune system and thus protect against the development of allergic diseases. H. pylori would suppress allergic immune-mediated inflammation through T helper type 1 (Th1)/Th2 paradigm, which is suppression of Th2 responses by stimulation of Th1 immunity. In contrast, H. pylori infection has been associated with extra-digestive pathologies including chronic idiopathic urticaria. Although systematic review demonstrated that eradication was associated with remission of urticaria, the association is still controversial and the pathogenic mechanisms have never been confirmed.