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."
