Eosinophils and pulmonary function: an epidemiologic study of adolescents and young adults

In order to identify potential risk factors, other than cigarette smoking, for lung function impairment, the relationships of peripheral eosinophil count, bronchial responsiveness to inhaled histamine, skin test reactivity and respiratory symptoms to pulmonary function results in a population sample of 665 adolescents and young adults, aged 13 to 23 years.

Case history, especially concerning smoking habits and respiratory symptoms, was obtained by interview and a self administered questionnaire. Pulmonary function, peripheral blood eosinophil counts, bronchial responsiveness to inhaled histamine and skin test reactivity to common allergens were measured using standard techniques. The relationships of peripheral blood eosinophil counts, symptoms of asthma, cigarette smoking, bronchial responsiveness and skin test reactivity were compared with FEV1, adjusted for age, sex, and height.

The peripheral eosinophil count was inversely correlated to FEV1 %predicted (P = .001); and subjects with eosinophilia (defined as > .25 x 10(9) l(-1)) had significantly reduced FEV1 %predicted compared with those without eosinophilia (95 +/- 13 %pred and 102 +/- 16 %predicted, respectively, P = .001). A close direct correlation was observed between blood eosinophils and histamine responsiveness (r = .60; P < .001). In nonatopic subjects (n = 382), the FEV1 %predicted was significantly lower in those with eosinophilia compared with those without. Subjects, who had never smoked, who were nonatopic and nonasthmatic, and who had no evidence of bronchial hyperresponsiveness, were found to have a weak but statistically significant inverse relation between eosinophil count and FEV1 %predicted (r = -.14, P = .04). In the same subgroup, subjects with eosinophilia (n = 27) had reduced FEV1 %predicted compared with those without (n = 177) (96 and 102, respectively, P < .05).

The findings of this study support the theory that the role of the eosinophil leukocyte in obstructive pulmonary diseases extends beyond its role in allergic reactions, suggesting that an increased number of blood eosinophils reflects an inflammatory reaction in the airways, which might lead to development of obstructive airflow limitation.