Endotoxin augments myeloid dendritic cell influx into the airways in patients with allergic asthma.
BACKGROUND
Epidemiologic studies have shown that exacerbation of asthma is modulated by environmental endotoxin. High levels of endotoxin are associated with asthma symptoms and the current use of asthma medication. However, the underlying mechanisms by which endotoxin modulates asthma are not completely understood.


OBJECTIVE
The aim of the study was to test whether endotoxin enhances the response of individuals with allergic asthma to allergen, and to determine if this interaction is associated with increased numbers of antigen-presenting cells in the airways.


METHODS
Seventeen subjects with mild allergic asthma underwent segmental challenge with allergen, endotoxin, and the combination of both in three different lung segments via bronchoscopy. The cellular influx including monocytes, myeloid dendritic cells (mDCs), and plasmacytoid dendritic cells (pDCs), as well as the level of cytokines, were assessed in bronchoalveolar lavage fluid obtained 24 hours after segmental challenge. Monocytes, mDCs, and pDCs were isolated and their capacity to induce T cell proliferation was determined.


RESULTS
Endotoxin enhanced the cellular response to allergen. The combination of allergen and endotoxin resulted in increased numbers of total cells, lymphocytes, neutrophils, eosinophils, monocytes, and mDCs, as well as increased levels of lipopolysaccharide-binding protein, IL-1alpha, IL-6, and tumor necrosis factor-alpha in the bronchoalveolar lavage fluid compared with allergen alone. Isolated mDCs but not pDCs induced a strong T cell proliferation in vitro.


CONCLUSIONS
Endotoxin augments the allergic inflammation in the lungs of individuals with asthma, and induces an enhanced influx of monocytes and functionally active antigen-presenting mDCs into the respiratory tract.
Schaumann
Frank
F
Fraunhofer Institute of Toxicology and Experimental Medicine, Nikolai-Fuchs-Str. 1, 30625 Hannover, Germany.
Müller
Meike
M
Braun
Armin
A
Luettig
Birgit
B
Peden
David B
DB
Hohlfeld
Jens M
JM
Krug
Norbert
N
D000328:Adult; D001249:Asthma / Q000276:immunology*; D001985:Bronchial Provocation Tests; D001992:Bronchoalveolar Lavage Fluid / Q000276:immunology; D018925:Chemokines / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism; D003713:Dendritic Cells / Q000378:metabolism*; D005260:Female; D006801:Humans; D007111:Immunity, Cellular; D008070:Lipopolysaccharides / Q000276:immunology*; D007959:Lymphocyte Culture Test, Mixed; D008297:Male; D009000:Monocytes / Q000378:metabolism; D022423:Myeloid Cells / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000378:metabolism; D013601:T-Lymphocytes / Q000378:metabolism
D018925:Chemokines; D016207:Cytokines; D008070:Lipopolysaccharides