Eosinophilia in the respiratory secretions of children with chronic respiratory diseases - Pathophysiology and diagnostic impact

The eosinophilic granulocytes are characteristic inflammatory cells in the respiratory mucosa of children and teenagers suffering from allergic rhinitis or allergic bronchial asthma. That is the basis for the concept of eosinophilic mucositis or eosinophilic bronchitis for such diseases in contrast to the neutrophilic mucositis or neutrophilic (purulent) bronchitis due to viral or bacterial infections. By means of their aggressive metabolites (major basic protein (MBP), eosinophilic cationic protein (ECP), eosinophilic protein X (EPX), or eosinophil-derived neurotoxin (EDN), eosinophilic peroxidase (EPO)) the eosinophils play a central role in the pathophysiology Of the transition from frequently relapsing obstructive bronchitis in early childhood due to infections to relapsing obstructive bronchitis of later childhood (= bronchial asthma) due to allergy, in most cases resulting from bronchial hyperreactivity. A significant secretory eosinophilia (i.e, more than 13% eosinophils in the cytological smears of nose, pharynx or the tracheo-bronchial wall), is an indicator for the existence of bronchial hyperreactivity, as a rule due to respiratory allergy. The intensity of the airway obstruction (nose, bronchus) does not correlate with the percentage of eosinophilia. Bronchoalveolar lavage (BAL) is not a suitable method for detecting secretory eosinophilia. Moreover, persistent eosinophilia of the respiratory secretions are a sensitive indicator for the continuous existence of inflammatory processes in the mucosa. Usually such cases require not only allergen elimination but also additional (topical) steroid administration. Bronchial asthma is under control only if the asthmatic symptoms and the lung function test have been normalized and the eosinophilia in the respiratory secretion has disappeared. The traditional counting of the eosinophils and the quantitative measurement of ECP give comparable results, but in many patients they can vary considerably. The counting of eosinophils should be given preference for routine cases (lower cost) whereas for large scale research the ECP determination can be more effective.