Effect of Inhaled Corticosteroids on Peripheral Blood Eosinophil Counts and Density Profiles in Asthma

Background: Inhaled corticosteroids are effective in the treatment of asthma and reduce bronchial hyperresponsiveness. We examined the effect of inhaled budesonide (1600 micrograms/day for 14 days) on the number and density profile of peripheral blood eosinophils in 10 patients with mild stable asthma in a double-blind, placebo-controlled, crossover trial.

Methods: At the end of each study period, blood was collected immediately before measurement of bronchial responsiveness calculated as the concentration of methacholine causing a 20% fall in forced expiratory volume in 1 second (PC20). Plasma leukocyte suspension obtained after sedimentation of blood with 46% dextran was layered on a Percoll continuous-density gradient. After centrifugation, 20 sequential aliquots of increasing density gradients were removed for differential counts. Eosinophils recovered from density of gradients less than 1.080 gm/ml were defined as hypodense.

Results: Budesonide treatment resulted in a fall in mean eosinophil count from 0.37 +/- 0.05 x 10(9) L-1 after placebo to 0.16 +/- 0.03 x 10(9) L-1 (p < 0.01). A significant reduction occurred in the hypodense eosinophil population from 51.6% +/- 4.3% after placebo to 38.1% +/- 3.1% after budesonide (p < 0.05). Mean log PC20 increased from -0.26 +/- 0.12 after placebo to -0.004 +/- 0.14 after budesonide (p < 0.01).

Conclusion: We conclude that inhaled steroid therapy reduces the number of circulating hypodense eosinophils, which is an effect that may underlie the improvement in bronchial hyperresponsiveness.