Allergist Thomas Platts-Mills and co-workers at the University of Virginia in Charlottesville measured antibody levels in 226 schoolchildren and related the numbers to levels of allergens from dust mites and cats measured in the children's homes. The scientists were surprised to find that children with the highest exposure to cat allergen actually had lower levels of IgE--the antibody that apparently triggers allergic reactions and asthma--than did children with moderate cat exposure. High cat exposure did trigger production of a second type of antibody: IgG, which doesn't elicit such a severe inflammatory response and which may help build tolerance. The cat response is quite different from that evoked by dust mites, where the greater the exposure, the more IgE antibodies are generated.

The study, which appears in the 10 March Lancet, adds to evidence that children living with cats are less likely than those in catless households to become allergic to the animals.

Bengt Bjorksten of Linköping University in Sweden says the research suggests there are probably other allergens that may protect some people against allergic responses. In fact, researchers have observed a similar response in beekeepers who seem immune to bee venom.