Analysis of induced sputum for studying allergen‐specific IgE antibodies in airway secretion from asthmatic patients

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Abstract
Allergen-specific IgE antibodies have been considered to play an important role in the pathogenesis of atopic asthma. However, studies on allergen-specific IgE antibodies in airway secretion from asthmatic patients are very rare compared with those in serum. The present study was undertaken to determine whether induced sputum might provide a useful method for analysing allergen-specific IgE antibodies in airway secretions from asthmatic patients. Specific IgE antibodies to house dust mite (HDM) antigen were measured in induced sputum from 10 HDM-sensitive asthmatic patients and 12 non-allergic controls by enzyme-linked immunosorbent assay. HDM-specific IgE was regarded as positive when the absorbance value was higher than mean + 2 SD of controls. Their antigen-binding characteristics were determined by immunoblot analysis. HDM-specific IgE was positive in induced sputum from seven of 10 HDM-sensitive asthmatics. The IgE binding to HDM antigen could be inhibited by fluid phase HDM antigen in a dose-dependent manner, not by mugwort antigen. Treatment of induced sputum with dithiothreitol decreased the antigen-specific bindings, and increased the non-specific bindings on the measurement of HDM-specific IgE. These effects were significant in a concentration of dithiothreitol greater than 0.05%. Immunoblot analysis revealed that HDM-specific IgE antibodies in induced sputum recognized the HDM antigens with molecular weights of 42, 34, 32, 25 and 14 kDa. These antigen binding characteristics were similar to those in serum. We conclude that analysis of induced sputum is a useful non-invasive method for studying allergen-specific IgE antibodies in airway secretion from asthmatic patients.