Endotoxin and Bronchial Inflammation in Asthma

Asthma, Inflammation, Lung Diseases

To evaluate airway inflammation in persons with asthma exposed to endotoxin, a common occupational air contaminant. Subjects are subsequently challenged with allergen.

BACKGROUND: Endotoxin (or lipopolysaccharide \[LPS\]) is a potent inflammatory stimulant which is found in ambient air in occupational settings. Asthma in the workplace is an increasingly significant problem. Asthma is characterized by airway inflammation and increased reactivity to both allergic and non-allergic stimuli. LPS is known to induced airway inflammation in normal subjects and to enhance airway reactivity in asthmatics. Additionally, both alveolar macrophages and mononuclear cells from asthmatics secrete higher amounts of cytokines (interleukins 1 and 8 \[IL-1, IL-8\] and granulocyte macrophage-colony stimulating factor \[GM-CSF\] ) than those from normals. Thus, it is likely that LPS enhances allergen-induced inflammation and that allergic asthmatics are more sensitive to the effects of LPS. Preliminary data show that exposure to low levels (250 ng/m3) of LPS at risk for four hours enhances both immediate responsiveness to inhaled allergen and allergen-induced eosinophils as observed in induced sputum. In the nasal airways of allergics, a single dose of 1,000 nanograms of LPS enhances polymorphonuclear leukocyte influx associated with allergen challenge. This latter finding also correlates well with baseline IL-8 and ECP levels, suggesting that constitutive airway inflammation enhances response to these stimuli. DESIGN NARRATIVE: The effect of endotoxin LPS (5,000 nanograms) is compared on airway inflammation and methacholine response and lung function in normals and asthmatics; the effect of LPS (500 nanograms) is compared on allergen-induced reactivity and inflammatory cell influx following LPS exposure (5,000 nanograms) in asthmatics, likely as a result of decreasing baseline inflammation. To examine potential cellular mediation of the effect of LPS in asthma, cytokine secretion of mononuclear cells to LPS of subjects responding to LPS (or those in whom LPS enhance response to allergen) is compared to those who did not respond. In vitro monocyte and in vivo airway responses of asthmatics who are responsive and non-responsive is compared to baseline sputum and nasal lavage fluid IL-8 and ECP to determine if either in vitro monocyte responses or IL-8 and ECP in readily obtained airway fluids may serve as biomarkers of LPS responsiveness and might be used as a marker for a LPS-response phenotype in humans for future mechanistic and intervention studies. Finally, practical data on the effect of LPS in asthmatics (at levels found in typical work settings) and the ability of standard anti-inflammatory therapy to protect asthmatic workers unavoidable exposed to LPS will be obtained. The study was renewed in 2001 and continues through December, 2005.

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