Effect of inhaled corticosteroids on peripheral blood eosinophil counts and density profiles in asthma

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.

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.

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).

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.