In sensitized subjects, exposure to the mite
allergen appears to be only one of several factors leading to
asthma. We hypothesized that in association with
allergen exposure,
endotoxin, a proinflammatory agent present in
house dust (HD), influences the severity of
asthma. Using a cross-sectional study design, we investigated a group of 69 consecutive dust mite (HDM)-sensitized subjects defined as having
rhinitis (n = 20) or
asthma (n = 49); the latter were evaluated functionally and clinically by three different scores and by their need for daily medication. Concentrations of Dermatophagoides pteronyssinus p I
allergen (
Der p I) (by two-site
monoclonal antibody enzyme-linked
immunosorbent assay [ELISA]),
guanine (by high-pressure liquid chromatography [HPLC]), and
endotoxin (by modified Limulus. amebocyte lysate assay) were measured in HD collected in duplicate from the mattresses and floors in each subject's home. The concentrations of
Der p I and of
guanine in HD collected from mattresses were significantly higher in asthmatic subjects than in those with
rhinitis (p < 0.05 and < 0.04, respectively). In subjects (n = 37) exposed to a high level of HDM
allergen (i.e.,
Der p I > or = 10 micrograms/g HD and/or
guanine > or = 0.10 mg/100 mg HD), the severity of
asthma was unrelated to mite
allergen concentration in HD. On the contrary, the severity of
asthma was related to concomitant exposure to
endotoxin in HD, since the concentration of HD
endotoxin was significantly and inversely correlated with FEV1 (p < 0.05), FEV1/FVC (p < 0.02), daily need for oral (p < 0.01) and inhaled (p < 0.01)
corticosteroids, daily need for beta 2 agonists (p < 0.001) and
xanthines (p < 0.01), and clinical scores such as the modified Aas score (p < 0.01). In HDM-sensitized subjects exposed to a high level of
allergen, the concentration of
endotoxin measured in HD is an important determinant of
asthma severity.