Airborne endotoxin in homes with domestic animals: implications for cat-specific tolerance

Although endotoxin is known to increase symptoms in allergic individuals, early exposure might decrease sensitization. Similarly, the presence of an animal in the home has been associated with decreased sensitization to animal allergens. It has been suggested that the effect of animals could be explained by increased endotoxin exposure.

We sought to investigate the effects of domestic animals on airborne endotoxin.

By using a silent particle collector, air was sampled over 24 hours in homes with or without animals. The total volume sampled was approximately 1000 m3, which provides quantities of allergen and endotoxin that can easily be measured with standard assays.

The quantity of endotoxin ranged from less than 0.5 to more than 500 pg/m3, whereas cat and dog allergen ranged from less than 0.002 to more than 5 ng/m3. Overall, the quantity of airborne endotoxin was not higher in homes with at least one animal. However, airborne endotoxin levels were significantly lower in homes with a cat compared with homes with a dog (P < .001). In keeping with this, there was a significant correlation between airborne Can f 1 and airborne endotoxin (r = 0.50, P < .01) but not between endotoxin and Fel d 1 (r = 0.17, P = .27).

The results demonstrate that endotoxin is present in the air of almost all homes. Although higher levels were seen in homes with a dog, similar levels might be present in homes with no animals. The results argue that the effects of cat ownership cannot be explained by increased exposure to endotoxin.