Journal Club: Friday December 2, 2011

Armistead Williams, MD (Tisch MS) presented the following article in Journal Club.

Article title: Hygiene Hypothesis and Autoimmune Disease

Reference: Graham A. W. Rook. Clinic Rev Allerg Immunol. November 2011 DOI 10.1007/s12016-011-8285-8

According to the hygiene hypothesis for the cause of multiple sclerosis (or “old friends” hypothesis, as the author has it), multiple sclerosis and other autoimmune diseases such as Crohn’s and celiac disease have seen hugely significant increases in incidence in the last two centuries since the rise of urbanization and the industrialization of agriculture as a result of the depletion of microbiota from our environment with whom H. sapiens co-evolved and upon whom our species became dependent early in our evolutionary history. The author points to two separate events in human history as triggering changes away from our evolutionary environment and toward the present environment of high incidence of autoimmune disease: the Neolithic revolution, c. 100kya, when humans transitioned from nomadic hunter-gatherer societies in which social units tended towards 100 members or fewer into larger, more permanently settled, agricultural communities; and the urban and industrial revolutions of the 19^th century to the present, featuring sanitation, chlorination, widespread antibiotics, etc. The author does not conjecture that modern hygiene per se is responsible for the rise in autoimmune symptoms, but rather that the loss of the immune-regulating gut biome of early evolutionary history creates conditions in which there is no counterbalance to immune-stimulating genes. The microbes responsible include many bacteria and helminthes, but importantly not viruses (except for hepatitis A), which entered the human ecosystem too late in our evolutionary history to meet the criteria for being an “old friend.”