The effect of inhaled leukotriene D-4 and methacholine on sputum cell differentials in asthma

The cysteinyl leukotriene LTE(4) has been shown to induce airway eosinophilia in asthmatics in vivo. This phenomenon has not yet been reported for LTD(4). Hence, we examined the effect of inhaled LTD(4) and a control bronchoconstrictor agent, methacholine, on cell differentials in hypertonic saline-induced whole sputum samples of 12 nonsmoking atopic asthmatic subjects (three women, nine men; 21 to 29 yr of age; FEV(1), 74 to 120% pred; PC(20)FEV(1) methacholine < 9.6 mg/ml). The study had a crossover, placebo-controlled design consisting of 4 d separated by greater than or equal to 1 wk. On each randomized study day, the subjects inhaled five serial doses of either LTD(4) (mean cumulative concentration: 95.7 mu M) or methacholine (mean cumulative concentration: 542 mM) or five doses of their respective diluents (PBS/ethanol or PBS). The airway response was measured by FEV(1), followed by sputum induction with 4.5% NaCl, 4 h postchallenge. Inflammatory cells (greater than or equal to 250) were counted twice on coded cytospins and expressed as percentages of nonsquamous cells. There was no significant difference in the maximal percent fall in FEV(1) from baseline between LTD(4) (mean +/- SEM, 49.5 +/- 4.4% fall) and methacholine (mean +/- SEM, 55.9 +/- 3.4% fall) (p = 0.11). LTD(4) induced a significant increase in the percentage of sputum eosinophils as compared with its diluent (mean +/- SD, 26.6 +/- 21.3% and 10.2 +/- 8.8%, respectively; p = 0.025), whereas a similar trend for methacholine failed to reach significance (mean +/- SD, 19.1 +/- 22.9% and 7.8 +/- 5.8%, respectively; p = 0.11). There was no significant difference in the changes in the percentage of sputum eosinophils between LTD(4) and methacholine (mean difference +/- SD, 7.5 +/- 12.5% eosinophils; p = 0.09). We conclude that LTD(4) induces eosinophilia in sputum of asthmatic subjects 4 h after inhalation. Our data suggest that LTD(4) recruits eosinophils into the airways of asthmatics in vivo, possibly by virtue of direct or indirect chemotactic properties, whereas an additional effect of vigourous airway narrowing per se cannot be excluded.