Dr. Garcia’s presentation last class on host-parasite interaction of gut microbes touched on what is known as the hygiene hypothesis. The hygiene hypothesis is a very relevant and interesting topic in connection to evolutionary medicine because it takes into account the history of human exposure to microbes and how our immunoregulatory circuits developed in relation to the presence of microorganisms, especially with gut and skin flora. There is even evidence of evolved dependence to some of these microorganisms due to coevolution. With the changes brought about by technological modernization, the decreasing presence of microbes in our immediate environment has exacerbated systems of inflammation to cause a growing set of chronic autoimmune diseases to emerge. This connection is described in great detail in the book The Hygiene Hypothesis and Darwinian Medicine, edited by Graham A. W. Rook, who is a prominent name in this field of study.

An article in Science Daily from March 2012 titled “Getting the Dirt on Immunity: Scientists Show Evidence for Hygiene Hypothesis” details new supporting evidence for the theory provided by Brigham and Women’s Hospital about this modern predicament. The hospital’s study specifically provided an underlying biological mechanism explaining the hypothesis for the first time in its history, using “germ-free mice” as models. These mice, which were completely lacking in bacteria or any other microbes, were compared to mice living in normal microbial environments and were found to have exaggerated displays of inflammation due to hyperactivity of a unique class of T cells previously linked to disorders such as asthma and colitis in the lungs and colon. Most important of the research’s findings was that exposure to microbes during the first years of life, even if they no longer were as adults, still led to normal immune function, showing the important of early immune conditioning to microbes.

Article: http://www.sciencedaily.com/releases/2012/03/120322142157.htm