"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 allergic reactions.

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 measurement.

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 allergies.

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.