An investigation of the clinical utility of serum interleukin-5 measurements in bronchial asthma patients

Abstract

Bronchial asthma has been identified as a chronic inflammatory airway disorder associated with cell infiltration (mainly eosinophils) and airway epithelial cell detachment caused by the activation of infiltrated cells. Interleukin-5 (IL-5), a cytokine closely related to the production and activation of eosinophils, has been shown to induce the proliferation and differentiation of eosinophils, prolong their survival, and to enhance the functions of mature eosinophils. We monitored clinically the changes in serum IL-5 concentrations in patients with bronchial asthma both during and after asthma attacks. The relationship serum IL-5 concentrations and the type and severity of bronchial asthma, as well as eosinophil counts in sputum, was investigated. We also measured changes in IL-5 concentrations during steroid therapy. IL-5 concentrations were significantly decreased during asthma attacks and after their relief (p < 0.001). An analysis of blood samples taken from 55 patients suffering asthma attacks showed that serum IL-5 concentrations were significantly higher in non-atopy-type asthma than in atopy-type asthma (p < 0.05). Serum IL-5 levels are highest in severe asthma, followed by moderate asthma (p < 0.001) and mild asthma (p < 0.001). Serum IL-5 concentrations during asthma attacks and eosinophil counts in sputum were closely correlated (r = 0.85). Serum IL-5 concentrations were below the limit of determination and decrease the number of eosinophils in sputum was noted in 15 patients whose asthma was well-controlled by the long-term inhalation of beclometasone. Serum IL-5 concentrations did not decrease below the limit of determination (even during attack-free periods) in patients whose disease could not be well controlled by 6-month inhalation therapy with beclometasone. In patients with major and moderate bronchial asthma attacks, serum IL-5 concentrations decreased as symptoms improved over time following the i.v. infusion of steroids, suggesting that steroids are effective in inhibiting the production of IL-5. Measurement serum IL-5 concentrations could be clinically useful in the determination of the pathology (e.g., severity) of bronchial asthma could serve as an index for the degree of control of asthma, and may be useful in determining the disease's long-term prognosis.