In their paper, lead author Dennis R. Ownby, MD, 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."