Exposure to endotoxin or other bacterial components might protect against the development of atopy

Background Several recent studies have shown that growing up on a farm conf ers significant protection against the development of atopy. These findings point particularly towards the importance of exposure to stable dust and f arm animals. It has furthermore been reported that endotoxin, an intrinsic part of the outer membrane of gram negative bacteria, is abundant in enviro nments where livestock and poultry is kept. The aim of this study was therefore to measure the level of environmental e ndotoxin exposure in homes of farmers' children, children with regular cont act to livestock and control children with no contact to farm animals. Methods Eighty-four farming and nonfarming families were identified in rura l areas in Southern Germany and Switzerland. Samples of settled and airborn e dust were collected in stables, and of settled dust indoors from kitchen floors and the children's mattresses. Endotoxin concentrations were determi ned by a kinetic Limulus assay. Results Endotoxin concentrations were highest in stables of farming familie s, but were also significantly higher indoors in dust from kitchen floors ( 143 EU/mg vs 39 EU/mg, P < 0.001) and children's mattresses (49479 EU/m(2) vs 9383 EU/m(2), P < 0.001) as compared to control children from nonfarming families. In addition, endotoxin levels were also significantly higher in mattresses and dust from kitchen floors in households where children had re gular contact to farm animals (38.6 EU/mg and 23340 EU/m(2), respectively) as compared to control subjects. Conclusion We propose that the level of environmental exposure to endotoxin and other bacterial wall components is an important protective determinant for the development of atopic diseases in childhood.