Eosinophil activity markers in peripheral blood have high predictive value for bronchial hyperreactivity in patients with suspected mild asthma

The present study aimed to evaluate the predictive value of eosinophils and markers of their activity for bronchial hyperreactivity (BHR) in a population of patients with recently developed clinical symptoms of asthma. The activation of eosinophils was estimated by measuring eosinophil cationic protein (ECP) in serum. In addition, flow cytometry was used to measure the expression of the EG2-epitope on intracellular ECP in eosinophils from peripheral blood. Twenty-eight consecutive patients with clinical history of asthma were studied. Of the 28 patients, 18 had a positive bronchial challenge test measured as PD₂₀≤ 1600 μg histamine. A significantly higher concentration of eosinophils and a trend to higher ECP in the peripheral blood was found in the hyperreactive group than in the nonreactive group. However, the intracellular expression of ECP did not correlate with the PD₂₀ value, and no significant difference between the groups was found. With one eosinophil activity marker, either serum ECP or EG2, BHR could be predicted in 70% of the patients. If we combined any two of the activity markers (serum ECP, EG2, or the percentage of eosinophils), the predictive value increased to 100%. We conclude that the blood eosinophil concentration, as well as, to some extent, serum ECP, has a high specificity for BHR in patients with recently developed clinical symptoms of asthma. Despite normal bronchial reactivity, some patients had signs of activated eosinophils, i.e., high serum ECP and increased EG2 expression. Thus, these markers may reflect early stages in the development of BHR. Our results also indicate that a combined evaluation of percentage of eosinophils and of eosinophil activity markers is of clinical value to predict BHR.