I've come across an article by Graham Rook titled Hygiene Hypothesis and Autoimmune Diseases that I think summarizes the hypothesis quite well. The premise of the article is that increased incidence of autoimmune diseases can be attributed to our (humans) changing environment over the past century, i.e. modern and sanitary environments. Think of how much cleaner we live, we have sewer systems to take our excrement far away from us, we no longer live in close proximity to our livestock, etc. In addition to some of the more obvious alterations of our environment, we've also changed our microbial ecology (or microbiome) of our gut with our modern diet. All these factors contribute to our immune system having to deal with less 'germs'.
Now to explain, briefly, the hygiene hypothesis. The argument goes like this; human beings and our extraordinary immune system evolved over the course of millions of years in the presence of stuff we as a modern society deem icky, such as bacteria, parasitic worms, and various viruses, our immune systems might very well need these 'germs' in order to maintain proper immune functions. Because our immune system evolved in tandem with 'germs', parasites and bacteria, our immune system learned to tolerate these 'germs' and in fact they play an essential role in proper immune function. And in the absence of our 'old friends', to use a term from the article, our immune systems are more likely to be dysfunctional and in turn, sometimes attacks our own tissues/cells in our body. This hypothesis has also been used to explain some observations in epidemiology relating to autoimmunity as well as allergies. I find this hypothesis extremely fascinating and would suggest reading the entire article cited below.
Rook, G. A. W. (2011). Hygiene Hypothesis and
Autoimmune Diseases. Clinical Reviews in Allergy & Immunology, 42(1),
5–15. doi:10.1007/s12016-011-8285-8
An additional reference:
Okada, H., Kuhn, C., Feillet, H., & Bach,
J.-F. (2010). The “hygiene hypothesis” for autoimmune and allergic diseases: an
update. Clinical & Experimental Immunology, 160(1), 1–9.
doi:10.1111/j.1365-2249.2010.04139.x
Makes sence, and the hypothesis seems to work. Your last comment about autoimmunity and allergies possibly being caused by lack of our 'old friends' is what I think part of the reason the human race seems to be more suseptiple to many genetic/self disorders. I beleive that we already have the genetic make up to have autoimmune disease or to have allergies. I think that it depends on our environmental exposure in our youth to determine which of these genes turn on or off durring development. The less environmental exposures you have the more likely these genes will not be stimulated to be able to do what they are suppose to do. I've alway wondered why and how this works with exposure. One example specifically that It seems like the opposite effect can happen as well, this is an example, if you get RSV as a child you are more likely to have allergies/athsma, so somethings that you are actually exposed to, such as your friendly little 'old guys' can actually cause things such as asthma. Guess this means we should all start rolling in some mud next time it rains but try not to get sick.
ReplyDeleteSide thought: even though human population is increasing in autoimmune diseases and allergies, it is increasing in age. We must be doing something right.
It kind of goes back to the nature-nurture debate,where our genetic makeup contributes to the ability of our immune systems to fight off infection.
ReplyDeleteHowever,to a large extent the environment is a contributory factor to the manner in which our bodies adapt and respond to exposure to pathogens or allergens.
If we take a child that was raised in a super clean environment and place them in dirt, am convinced they would probably get very ill. Conversely a child that plays in the dirt almost always, would be better able to adapt or not even repond to any pathogens that maybe in the dirt.
Genes matter but the environment has a lot to do with it, by environment many things come to mind. Diet, healthcare system,social structures, sanitation etc all these matter in the progression of any kind of disease.
Exposure to common allergens may improve adaptability and lessen adverse responses and exposure to parasites may improve adaptability although these parasites increase morbidity and mortality.
Have you heard of the American Gut project? It's kind of cool, and related to the hygiene hypothesis. A whole group of microbiologists are banding together to collect stool and saliva samples from people across the US (and their pets). It costs some money to participate, and they send you a kit to do your samples. You have to keep a thorough dietary record for a few days and answer some background questions. They analyze your microbiome, and you can compare your gut to the guts of other people across the country. I think they are also hoping to work with people in a pretty remote area of southern Africa to get a sense of the non-westernized microbiome for comparison.
ReplyDeleteI think it's pretty cool. And the data are housed at our very own CU Boulder. One of the professors there, Rob Knight, has done a lot of work in this area.
Check it out:
http://humanfoodproject.com/american-gut/