House Dust Endotoxin and Allergic Sensitization in Children  
Gehring U, Bischof W, Fahlbusch B, Wichmann HE, Heinrich J
American Journal of Respiratory and Critical Care Medicine. 2002;166(7):939-944
 
INTRODUCTION Several studies have linked endotoxins, components of the outer membrane of Gram-negative bacteria, to strong proinflammatory immune system responses.^[1,2] The data defining the role of endotoxins in asthma have, however, presented conflicting views. While some studies suggest that endotoxins trigger asthmatic responses by inducing an airway inflammation,^[3] others seem to indicate that endotoxin exposure activates type-1 T-helper cell responses, thus having a protective effect on atopy.^[4] This German study examined the association between house dust endotoxin and allergic sensitization in children growing up on a farm.
 
METHODS Seven hundred forty children, aged 5 to 10 years, were screened via a 78-item cross-sectional survey, and data from 444 children were selected for inclusion in this study. Of the children selected for inclusion, 50% were atopic or had physician-diagnosed asthma. All of the children included in this data set completed IgE testing for house dust mite Dermatophagoides pteronyssinus (d1), cat dander (e1), grass pollen (g6), birch pollen (t3), and Cladosporium herbarum (m2). In addition, dust samples collected by vacuuming the living room floors in their homes were taken and analyzed for the presence of endotoxins.
 
RESULTS The endotoxin levels collected from the living room floors ranged from 160 to 2,670,001 EU/m², with geometric mean of 24,221 (4.1) EU/m². Overall, 23% of the children's parents were found to be atopic, and 22% of the families lived with an indoor dog and/or cat. The data revealed a negative association between exposure to endotoxins and a sensitization to 1 or more allergens (aOR [95% CI] 0.95 [0.83; 1.10]) and 2 or more allergens (aOR [95% CI] 0.80 [0.67; 0.97]). Children who had lived in the same home since birth were found to have a stronger protective effect by endotoxin exposure on sensitization to indoor allergens than children who had moved to a new home at least once during their lifetime.
 
CONCLUSION Based on these data, the researchers concluded that exposure to higher levels of house dust endotoxin has a protective effect and is associated with lower prevalence of allergic sensitization in children.
 
REFERENCES

1. Douwes J, Pearce N, Heederik D. Does environmental endotoxin exposure prevent asthma? Thorax. 2002;57:86-90.
2. Michel O, Kips J, Duchateau J, et al. Severity of asthma is related to endotoxin in house dust. Am J Respir Crit Care Med. 1996;154:1641-1646.
3. Michel O, Duchateau J, Sergysels R. Effect of inhaled endotoxin on bronchial reactivity in asthmatic and normal subjects. J Appl Physiol. 1989;66:1059-1064.
4. Gereda JE, Leung DYM, Thatayatikom A, et al. Relation between house-dust endotoxin exposure, type 1 T-cell development, and allergen sensitization in infants at high risk of asthma. Lancet. 2000;355:1680-1683.

 
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