FRIDAY, June 16, 2006 (HealthDay News) -- A study comparing wild and laboratory rodents supports the notion that exposing immune systems to naturally occurring germs helps build a defense against illness.
In the study, Duke University researchers compared mice and rats living in laboratories to those captured in the wild. The team analyzed and compared the rodents' immune systems.
"Laboratory rodents live in a virtually germ- and parasite-free environment, and they receive extensive medical care -- conditions that are comparable to what humans living in Westernized, hygienic societies experience," senior researcher William Parker, an assistant professor of experimental surgery, said in a prepared statement.
"On the other hand, rodents living in the wild are exposed to a wide variety of microbes and parasites, much like humans living in societies without modern health care, and where hygiene is harder to maintain," they said.
Scientists have studied this theory before, and hypothesize that people living in a "hygienic" environment are less protected against allergies and autoimmune diseases simply because their immune systems have never been exposed to such parasites.
To determine if the hypothesis could be confirmed, the researchers analyzed the rodents' immunoglobulin antibodies relating to allergy and autoimmune disease. They compared the levels of IgG, associated with autoimmune diseases, and IgE, known to protect the body from parasites, in rodents from each environment.
The results -- just published online in the Scandinavian Journal of Immunology -- showed that the wild rodents had significantly higher levels of IgE than the laboratory rodents, and modestly higher levels of IgG.
"The most commonly accepted explanation for this high incidence of allergy and perhaps autoimmune disease is the hygiene hypothesis," said Parker. However, more thorough studies concentrating on specific parasites need to be conducted, Parker noted.
Allergies affect nearly 50 million Americans, while autoimmune disorders -- including type 1 diabetes, rheumatoid arthritis, lupus and scleroderma -- affect another 8 million.
"These results appear to demonstrate that the environment has profound effects on the production of IgE and autoreactive IgG," said Parker. "These results are consistent with the idea that animals without access to modern medicine have high levels of autoimmune-like and allergic-like immune responses that represent appropriate responses to unknown factors in their environment."
The Medical College of Wisconsin has more information on the hygiene hypothesis.