Background: Leukotriene-E4 (LTE4) and prostaglandin-D2 (PDG2) are lipid mediators associated with Type-2 inflammation in asthma. Both are increased in the urine of patients with asthma. We have assessed concentrations in induced sputum in patients with asthma and tested the hypothesis that concentrations vary according to the pattern of inflammation.

Methods: Induced sputum was obtained from 7 healthy volunteers and 44 patients with asthma (GINA steps 2-5), and processed according to our usual procedures. LTE4 and PGD2 were measured using commercially available ELISA kits. Patients with asthma were stratified by induced sputum eosinophil count, with counts > 3% classified as eosinophilic.

Results: Geometric mean (log SD) LTE4 concentration was 218 (0.47), 1237 (0.44) and 5541 (0.94) pg/ml and PGD2 concentration 2289 (0.2), 3366 (0.33) and 4575 (0.3) pg/ml in controls, patients with non-eosinophilic and patients with eosinophilic asthma respectively (figure). LTE4 was significantly different across groups by one-way ANOVA (p=0.0005). No difference was seen between mild-moderate (GINA 2-3) and severe asthma (GINA 4-5) groups or in patients with a self-reported aspirin sensitivity (shown as open data points).

Conclusion: LTE4 is increased in the sputum of patients with asthma compared to healthy controls, and in eosinophilic compared to non-eosinophilic asthma. Our data does not support a specific role in patients with severe asthma or in patients with aspirin sensitivity.