Corticosteroid suppression of lipoxin A4 and leukotriene B4from alveolar macrophages in severe asthma

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Abstract
An imbalance in the generation of pro-inflammatory leukotrienes, and counter-regulatory lipoxins is present in severe asthma. We measured leukotriene B4 (LTB4), and lipoxin A4 (LXA4) production by alveolar macrophages (AMs) and studied the impact of corticosteroids. AMs obtained by fiberoptic bronchoscopy from 14 non-asthmatics, 12 non-severe and 11 severe asthmatics were stimulated with lipopolysaccharide (LPS,10 μg/ml) with or without dexamethasone (10-6M). LTB4 and LXA4 were measured by enzyme immunoassay. LXA4 biosynthesis was decreased from severe asthma AMs compared to non-severe (p < 0.05) and normal subjects (p < 0.001). LXA4 induced by LPS was highest in normal subjects and lowest in severe asthmatics (p < 0.01). Basal levels of LTB4 were decreased in severe asthmatics compared to normal subjects (p < 0.05), but not to non-severe asthma. LPS-induced LTB4 was increased in severe asthma compared to non-severe asthma (p < 0.05). Dexamethasone inhibited LPS-induced LTB4 and LXA4, with lesser suppression of LTB4 in severe asthma patients (p < 0.05). There was a significant correlation between LPS-induced LXA4 and FEV1 (% predicted) (rs = 0.60; p < 0.01). Decreased LXA4 and increased LTB4 generation plus impaired corticosteroid sensitivity of LPS-induced LTB4 but not of LXA4 support a role for AMs in establishing a pro-inflammatory balance in severe asthma.

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