"The striking finding here is that high pet exposure early in life
appears to protect against not only pet allergy but also other types of
common allergies, such as allergy to dust mites, ragweed, and grass,"
says Marshall Plaut, M.D., chief of the allergic mechanisms section at
NIAID. "Other studies have suggested a protective effect of pet exposure
on allergy and asthma symptoms, but generally have looked only at
whether pet exposure reduced pet allergy. This new finding changes the
way scientists think about pet exposure; scientists must now figure out
how pet exposure causes a general shift of the immune system away from
an allergic response."
In their paper, lead author Dennis R. Ownby, M.D., of the Medical
College of Georgia, and colleagues suggest that bacteria carried by pets
may be responsible for suppressing the immune system's allergic
response. These bacteria release molecules called endotoxins, and
endotoxins are believed to shift the developing immune system away from
responding to allergens through a class of lymphocytes called Th-2
cells, which are associated with allergic reactions. Instead, endotoxins
may stimulate the immune system to activate Th-1 cells, which may block
The researchers followed 474 children from birth to six or seven
years of age. When the children were one year old, the researchers
contacted parents by telephone to find out how many pets were in the
home. When the children were two years old, researchers measured the
level of dust mite allergen in their bedrooms. When the children were
six or seven, the researchers tested them for allergic antibodies to
common allergens by two approaches - a skin prick test and a blood
After adjusting for factors such as dust mite allergen levels,
parental smoking, and current dog or cat ownership, the researchers
found that children exposed to two or more dogs or cats during the first
year of life were on average 66 to 77 percent less likely to have any
allergic antibodies to common allergens, as compared with children
exposed to only one or no pets during their first year.
"Our findings suggest an area of research with many possibilities,
one that could potentially bear fruit over the next decade or so," says
Dr. Ownby. "If we could find out exactly what it is about pets or the
bacteria they carry that prevents the allergic response, scientists
might be able to develop a new allergy therapy based on that knowledge."
NIAID is a component of the National Institutes of Health (NIH).
NIAID supports basic and applied research to prevent, diagnose, and
treat infectious and immune-mediated illnesses, including HIV/AIDS and
other sexually transmitted diseases, illness from potential agents of
bioterrorism, tuberculosis, malaria, autoimmune disorders, asthma and
NIEHS is the component of NIH that conducts and supports research on
the environmental causes and triggers of disease and our human
susceptibility to them.
Press releases, fact sheets and other NIAID-related materials are
available on the NIAID Web site at http://www.niaid.nih.gov.
The National Institute of Allergy and Infectious Diseases is a
component of the National Institutes of Health, U.S. Department of
Health and Human Services.
this page for much more information about dust mites and how to control them.
Source page: http://www.nih.gov/news/pr/aug2002/niaid-27.htm