Mechanism of Action
Allergic diseases are caused by inappropriate immunological responses to harmless antigens driven by a Th2-mediated immune response. Many bacteria and viruses elicit a Th1-mediated immune response, which down-regulates Th2 responses. The first proposed mechanism of action of the hygiene hypothesis stated that insufficient stimulation of the Th1 arm, stimulating the cell defence of the immune system, leads to an overactive Th2 arm, stimulating the antibody-mediated immunity of the immune systems, which in turn led to allergic disease.
The first proposed mechanistic explanation for the hygiene hypothesis cannot explain the rise in incidence (similar to the rise of allergic diseases) of several Th1-mediated autoimmune diseases, including inflammatory bowel disease (IBD), multiple sclerosis (MS), and type I diabetes. The major proposed alternative mechanistic explanation is that the developing immune system must receive stimuli (from infectious agents, symbiotic bacteria, or parasites) in order to adequately develop regulatory T cells, or it will be more susceptible to autoimmune diseases and allergic diseases, because of insufficiently repressed Th1 and Th2 responses, respectively.
Read more about this topic: Hygiene Hypothesis
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