Atopic asthmatic patients have reduced airway inflammatory cell recruitment after inhaled endotoxin challenge compared with healthy volunteers

Abstract

Background: Atopic asthmatic patients are reported to be more sensitive to the effects of environmental endotoxin (LPS) than healthy volunteers (HVs). It is unknown whether this sensitivity is due to dysregulated inflammatory responses after LPS exposure in atopic asthmatic patients.

Objective: We sought to test the hypothesis that atopic asthmatic patients respond differentially to inhaled LPS challenge compared with HVs.

Methods: Thirteen allergic asthmatic (AA) patients and 18 nonallergic nonasthmatic subjects (healthy volunteers [HVs]) underwent an inhalation challenge to 20,000 endotoxin units of Clinical Center Reference Endotoxin (LPS). Induced sputum and peripheral blood were obtained at baseline and 6 hours after inhaled LPS challenge. Sputum and blood samples were assayed for changes in inflammatory cell numbers and cytokine and cell-surface marker levels on monocytes and macrophages.

Results: The percentage of neutrophils in sputum (%PMN) in induced sputum similarly and significantly increased in both HVs and AA patients after inhaled LPS challenge. However, the absolute numbers of leukocytes and PMNs recruited to the airways were significantly lower in AA patients compared with those seen in HVs with inhaled LPS challenge. Sputum levels of IL-6 and TNF-α were significantly increased in both cohorts, but levels of IL-1β and IL-18 were only significantly increased in the HV group. Cell-surface expression of Toll-like receptors 4 and 2 were significantly enhanced only in the HV group.

Conclusions: The airway inflammatory response to inhaled LPS challenge is blunted in AA patients compared with that seen in HVs and accompanied by reductions in airway neutrophilia and inflammasome-dependent cytokine production. These factors might contribute to increased susceptibility to airway microbial infection or colonization in AA patients.

FIG 1

%PMNs in sputum before and after inhaled LPS challenge. %PMNs significantly increased in both cohorts, with no significant difference in post-LPS–pre-LPS %PMNs between groups. Lines represent means (n = 18 HVs and 13 AA patients).

FIG 2

Leukocyte numbers in induced sputum and peripheral blood. Sputum, Absolute numbers of total leukocytes (cells per milligram, A) and neutrophils (PMNs per milligram, B) in induced sputum before (pre-LPS) and after (post-LPS) challenge. Blood, Total numbers of WBCs (C) and PMNs (D) in the blood of HVs and AA patients with LPS challenge. Lines represent means (n = 18 HVs and 13 AA patients).

FIG 3

Proinflammatory cytokines recovered from induced sputum. Mean concentrations of TNF-α (A), IL-6 (B), IL-1β (C), and IL-18 (D) measured in induced sputum supernatants before LPS and after LPS challenge are shown. Means and SEMs are shown (n = 18 HVs and 12 AA patients).

FIG 4

Monocyte and macrophage surface marker expression from induced sputum. Monocytes, Mean fluorescence intensity (MFI) of TLR4 (A) and CD14 (B) before and after LPS challenge in HVs and AA patients. Macrophages (mΦ), MFI of TLR4 (C), CD14 (D), TLR2 (E), and CD11b (F) before and after LPS challenge. Means with SEMs are shown (n = 13 HVs and 7 AA patients).