# 5142
Note: The `Hygienic Hypothesis’ – while something I personally find fascinating to write about - remains an unproven theory, and so what follows needs to be taken in that light.
Similarly, mouse studies, while often useful in medical research, don’t always predict what happens in human physiology.
In the past several weeks the hygienic hypotheses has made headlines a number of times, something I covered late last month in Study: Bisphenol A, Triclosan and The Hygienic Hypothesis, and Maryn McKenna wrote about here and here.
In brief, the `Hygienic Hypothesis’ is a theory that suggests some of the allergies and autoimmune diseases common to modern man come about due to a lack of exposure to certain biological agents (bacteria, viruses, and even parasites) . . . particularly in early childhood.
Research over the past decade has increasingly linked the use of household cleaners (bleach, disinfectants, carpet cleaners, etc) and other chemicals (turpentine, insecticides, etc) to childhood onset asthma and allergies (see MedNews Today Asthma in kids linked to household cleaning products and chemicals).
Essentially, the hygienic hypothesis says we may be trying to be `too clean’ for our own good.
One of the more controversial aspects of this theory is that intestinal parasites (ie. worms) – which have been largely eliminated in the western world - are actually beneficial, and can help prevent (or even cure) certain types of inflammatory bowel disease.
NPR (along with many other media outlets) covered this story at length a couple of weeks ago (see Eat Your Worms: The Upside Of Parasites).
Today, a new study appears in the Journal of Clinical Investigation, that lends additional support to the hygienic hypothesis.
It looks at the protective effects of certain types of viral infections in suckling mice against adult onset asthma. Before you scoff, this research has a pretty impressive pedigree.
A link, and a couple of excerpts from the abstract (follow the link to read it in its entirety) follow:
Ya-Jen Chang, Hye Young Kim, Lee A. Albacker, Hyun Hee Lee, Nicole Baumgarth, Shizuo Akira, Paul B. Savage, Shin Endo, Takashi Yamamura, Janneke Maaskant, Naoki Kitano, Abel Singh, Apoorva Bhatt, Gurdyal S. Besra, Peter van den Elzen, Ben Appelmelk, Richard W. Franck, Guangwu Chen, Rosemarie H. DeKruyff, Michio Shimamura, Petr Illarionov, Dale T. Umetsu
J. Clin. Invest. 2010; doi:10.1172/JCI44845
Infection with influenza A virus represents a major public health threat worldwide, particularly in patients with asthma. However, immunity induced by influenza A virus may have beneficial effects, particularly in young children, that might protect against the later development of asthma, as suggested by the hygiene hypothesis.
Herein, we show that infection of suckling mice with influenza A virus protected the mice as adults against allergen-induced airway hyperreactivity (AHR), a cardinal feature of asthma.
<SNIP>
These findings suggest what we believe to be a novel pathway that can regulate AHR, and a new therapeutic strategy (treatment with glycolipid activators of this NKT cell population) for asthma.
Basically researchers infected 2-week old (suckling) mice and 8-week old (adult) mice with with the A/Mem71 (H3N1) influenza virus. Six weeks later both cohorts were tested for susceptibility to an asthma-like reaction.
Mice that were infected at 2-wks of age were protected against an asthma-like reaction.
Those infected as adults were not.
The reason given for this protective effect was an increase in certain types of NKT (natural killer T-cells) in baby mice post-infection, something which was not observed in the influenza-challenged adult mice.
Interestingly, the researchers also found that a molecule produced by the stomach bacteria Helicobacter pylori also produced a protective affect against asthma in adult mice, giving hopes for a new avenue of research into better treatments.
The article is lengthy, technical, and open access. I’ve only scratched the bare surface with this overview. Those interested in learning more should follow this link to read the entire study.
Before anyone decides to eat worms, stop bathing, or move down to the city sewers for their health . . . remember:
The hygienic hypothesis is still just a theory.
