Eosinophilic inflammation is associated with elevation of interleukin-5 in the airways of patients with spontaneous symptomatic asthma

In vitro and in vivo studies have shown an important role for interleukin-5 (IL-5) in regulating eosinophil proliferation, survival, and effector function. Because eosinophilic inflammation is an important component of symptomatic episodes of asthma, we have investigated whether increased levels of IL-5 protein are present in bronchoalveolar lavage (BAL) fluid of patients with spontaneously symptomatic asthma (FEV₁, 61% predicted; FEF_25%-75%, 30% predicted) compared with patients with asymptomatic asthma (FEV₁, 88% predicted; FEF_25%-75%, 76% predicted). The percent of BAL eosinophils (10.5% vs 0.6%) (p = 0.0001) and eosinophil-derived neurotoxin (386.0 ng/ml vs 6.3 ng/ml) (p = 0.0001) was greater in BAL fluids derived from patients with symptomatic asthma compared with patients with asymptomatic asthma. Levels of IL-5 measured with an immunoradiometric assay were significantly higher in patients with symptomatic asthma (n = 26) compared with those with asymptomatic asthma (n = 18) (274 pg/ml vs <13 pg/ml) (p = 0.02). The increased IL-5 levels were noted in a subset of patients with symptomatic asthma with BAL absolute eosinophil counts greater than 10⁶ (IL-5, 664 pg/ml; n = 10) as opposed to patients with symptomatic asthma with BAL eosinophil counts less than 10⁶ (IL-5, <13 pg/ml; n = 16) (p = 0.005). This study suggests that IL-5 is not only induced in experimental models of allergen-induced asthma but can also be detected as asthma progresses from the asymptomatic to the clinically symptomatic state in subjects with significant BAL eosinophilia. (J ALLERGY CLIN IMMUNOL 1995;96:661-8.).