The biodiversity hypothesis and immunotolerance in allergy.

Background: The human immune system is capable of detecting a multitude of substances and organisms in the environment and responding to these in a variety of ways. This includes immune responses to pathogens, on the one hand, and immunotolerance in the form of immunoregulatory responses, resulting in either the termination of immune responses or in tolerance to harmless and endogenous substances, on the other. The development of immunotolerance is an active process that is essentially characterized by interaction with microbiota and environmental components and is primarily mediated by regulatory T cells. Methods: This article provides an overview of selected scientific articles and is addressed also to non-specialists. It is based on a literature search in PubMed, specialist databases, and guidelines. Results: According to the diversity hypothesis, exposure in early childhood to broad biodiversity is now considered to reduce the risk of developing allergic diseases. Conclusion: Therefore, tolerance induction emerges in allergology not only as a potential concept for prevention, but also as a treatment approach in atopic diseases