Relationship between increased hypodense eosinophils in the peripheral blood and bronchial hyperresponsiveness in patients with bronchial asthma.

Eosinophils are the most prominent inflammatory cells involved in the development of bronchial hyperresponsiveness in bronchial asthma. There is evidence that eosinophils in the peripheral blood are a heterogeneous cell population. The heterogeneity of eosinophils in the peripheral blood from 16 patients with mild to moderate bronchial asthma and seven normal subjects was studied using Percoll density fractionation. Eosinophils recovered from patients with bronchial asthma were mainly in the lower density fractions (< 1.095 g/mL), whereas eosinophils from normal subjects were in the higher density fractions (> 1.095 g/mL). The total cell count and the proportion of hypodense eosinophils were highly correlated with the provoking concentration (PC20) of methacholine, which caused a 20% decrease in FEV1 but not in the baseline spirometry. Disease severity, determined on the grounds of clinical history and the peak expiratory flow rate as well as its variability, showed that patients with moderate bronchial asthma had a higher count of hypodense eosinophils than those with mild bronchial asthma. This study shows that eosinophils from asthmatics, when compared with those from control subjects, are heterogeneous and predominantly hypodense cells. Changes in the repartition of the eosinophil subpopulations may be of critical importance in determining the magnitude of the inflammatory response of the airways in bronchial asthma.