Endotoxin is a part of the cell wall of common bacteria in the environment. The authors note that inhaled endotoxin produces a marked inflammatory response in the lungs, and it may cause the airways of people with asthma to constrict. In previous studies, endotoxin has been shown to enhance the inflammatory effect of diesel exhaust particulate, inhaled highway aerosols and ozone in the lungs of experimental animals.
"There's experimental literature that shows both allergens and endotoxin interact with air pollution and increase the effect of each other," says McConnell. "But there's been very little study to see if these experiments have relevance for the general population of children with asthma."
McConnell cautioned that much more study is needed to specify why, exactly, children with asthma living in homes with dogs had an enhanced response to air pollution.
"There are other possible explanations for the findings," he says, "and actual measurements of home allergen and endotoxin, in addition to air pollution, would be important to evaluate further our hypothesis. It could also be that something only indirectly related to dogs could explain these results, for example that kids with dogs exercise outside more so they have more exposure to air pollution."