Characteristics of peripheral blood eosinophils in patients with nocturnal asthma

A number of mechanisms have been proposed to explain nocturnal exacerbations of asthma including circadian patterns in circulating cortisol and catecholamines. These factors may influence airway smooth muscle tone and circulating eosinophil characteristics and function. Because recent evidence has indicated that eosinophils contribute to airway inflammation and the severity of asthma, we evaluated the relationship among peripheral blood eosinophils, their density distribution, and the appearance of nocturnal asthma. Fifteen patients with asthma were evaluated. Spirometry (FEV₁ and FVC) was determined at 0400 and 1600, and the number and density distribution of peripheral blood eosinophils were determined. Five patients had nocturnal asthma, defined as a 15% or greater fall in FEV₁ at 0400 versus 1600. The patients with nocturnal asthma had greater numbers of eosinophils (cells x 10³/ml) at 0400 (0.845 ± 0.13 versus 0.351 ± 0.03) and 1600 (0.651 ± 0.18 versus 0.319 ± 0.07) and a greater circadian variation with peak eosinophilla at 0400. Furthermore, we found a significant circadian increase in low-density eosinophils (as determined by Percoll density gradient centrifugation) at 0400, but only in patients with nocturnal asthma. These observations suggest that a circadian variation in low density eosinophils may contribute to nocturnal exacerbations of asthma.