"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
Contact: Gregory Roa
NIH/National Institute of Allergy and Infectious Diseases