[Theophylline reduces serum levels of ECP in vitro]

Measurement of serum levels of ECP has been widely used for monitoring airway inflammation in bronchial asthma and recently been applied to measure anti-inflammatory effect of theophylline. However, reduced levels of ECP in theophylline-administered patients may express not only in vivo effect of theophylline but also in vitro effect after sampling because serum ECP measures released ECP during coagulation and theophylline has been reported to inhibit eosinophil degranulation in vitro. In order to answer the question, we tested whether theophylline added to blood after sampling reduces measured levels of serum ECP. Various concentrations of theophylline were added to SST tube, to which venous blood from atopic patients was drawn. Serum was, then, obtained by centrifugation after 15 min to 6 hours of incubation at room temperature. Theophylline significantly reduced serum ECP in a concentration-dependent manner. Percent reduction of ECP levels at 1 hour of incubation were 11.9%, 18.7%, 22.8%, and 51.7% at theophylline levels of 5, 12.5, 22.5, and 120 micrograms/ml, respectively. Kinetics of serum ECP release was also inhibited in the presence of theophylline. These results suggest that in vitro effect of theophylline on serum ECP levels should be considered when data of serum ECP in patients who take theophylline are interpreted.