Inhibition of allergic disorders by infection with bacteria or the exposure to bacterial products

The incidence, severity, and mortality rare of allergic diseases, such as asthma, aropic dermaritis and rhinitis is increasing in the developed nations of the world, despite the use of steroids and other drugs. The reason for this development is unknown, but has been speculated to be due to a steady decline in infecrious diseases. This view is supported by recent epidemiological and experimental findings showing that bacterial infections have the capacity to inhibit the development of allergic disorders. In addition, the exposure to bacterial products such as lipopolysaccharide (LPS) or bacterial DNA is also associated with a decrease in allergen-specific Th2 responses. Although the immunological mechanisms responsible for these protective effects are ill defined, recent publications indicate that they are associated with the induction of Th1 or T regulatory responses. This review focuses on experimental and epidemiological studies addressing the question if bacterial infections or the exposure to bacterial products can inhibit the development of allergic responses.