The hygiene hypothesis in allergy and autoimmunity

 

In the last decades the industrialized countries have observed a rise not only of allergic disease, but also of some auto-immune or inflammatory diseases, such as type 1 diabetes mellitus, multiple sclerosis or Crohn’s disease. The hygiene hypothesis (HH) suggests, that an early exposure to micro-organisms is able to prevent some of these diseases. While the HH initially explained the rise of allergic disease (immunologic Th2 type), applying the paradigm of an imbalance in the Th1/Th2 status, it was later observed, that this paradigm did not well fit to the simultaneous rise of other Th1 associated auto-immune diseases.

            Thus the revised HH applies the idea of a defective immuno-regulation in the sense of a lack of inhibitory or regulatory features against maintained Th1 or Th2 responses. The evolutionary focus states that the immune system is not able to follow the velocity of the rising cultural adaptation of the human being to new environments from the beginning of agriculture. The immune system, like the brain, is a system, which needs the appropriate signals for which it has evolved. The environment, where we are living has changed radically with respect to micro-organisms and parasites. On one side, we are exposed to less parasites and infectious disease in general, on the other side it seems that the intestinal micro-flora has changed.

            We will show evidence within different research areas (epidemiology, immunology…), which underlines the concept, that the lack of contact with micro-organisms and parasites could explain the rise in allergic and some auto-immune disease. This could be translated directly to new therapeutic concepts, such as recent ones, where this evolutionary idea has been applied, and where infection with live parasites are used to treat allergy and auto-immunity.