Differential Excretion of Urinary Eosinophil Protein X after Methacholine Challenge Test in Children with Asthma

ABSTRACT

PURPOSE: Eosinophil is one of the important inflammatory cell involved in the airway inflammation in childhood asthma. It has been demonstrated that markers of eosinophil activation, including eosinophil cationic protein or eosinophil protein X(EPX), are increased in childhood asthma. Furthermore, they are related to disease activity and are assumed to be helpful in monitoring the treatment effect as urinary EPX(U-EPX) can be obtained easily and in a noninvasive way in children of all ages. METHODS: Twenty-five children(22 male and three female) aged 11.87+/-3.82 years with stable asthma were challenged with methacholine and urine was collected from each child during the following periods; before methacholine challenge test(MCT); 0-3 hr after the end of MCT; 4-7 hr after the end of MCT; and 8-24 hr after the end of MCT. Bronchial reactivity was determined by using Dosimeter(Jeager, Germany) with serially diluted methacholine from 0.05 to 25.0 mg. The FEV1 less than 80% of baseline value were classified into positive MCT. U-EPX was measured with a sensitive and specific radioimmunoassay(Pharmacia & Upjohn AB, Uppsala, Sweden). Results were expressed as microgramEPX/mmol creatinine. RESULTS: An early airway response after MCT was associated with an increase of U-EPX excretion for 0-3 hr after methacholine inhalation in comparison with beseline values. Most subjects showed a small increase in U-EPX excretion during late asthmatic response for 4-7 hr, which then decreased to normal level in 8-24 hr. Also, a tendency for a higher increase of U-EPX was associated with a lower threshold of methacholine challenge and a longer duration of asthma. CONCLUSION: Measurement of EPX in urine is a noninvasive and easy method to assess the severity of airway inflammation in asthmatic children. It may be a helpful index of the events underlying the airway inflammatory responses during nonspecific bronchial challenge, and in monitoring asthma management.