[Basic research into the measurement of eosinophil cationic protein (ECP) in blood samples]

Eosinophil cationic protein (ECP), which is one of the eosinophil granule proteins, can now be measured with a radioimmunoassay kit. However, the level of ECP in blood samples is affected by the method of treatment of the samples. We investigated the effect on ECP level of a variety of treatment methods to establish the fundamental condition for the measurement of ECP level in blood samples. ECP levels in serum or heparin plasma increased time-dependently until 2 hr. This increase was considered to be due to active in vitro release of ECP from eosinophils. Serum ECP level at 1 hr was temperature-dependent, being higher at 37 degrees C than at 25 degrees C. On the other hand, ECP level in EDTA plasma did not change significantly during a 3 hr period, and this level of ECP was considered to be that which had been released into the blood in vivo. ECP levels were always in the order of serum greater than heparin plasma greater than EDTA plasma. Though there was a positive correlation between serum ECP level and peripheral blood eosinophil count, the degree of correlation was not strong (r = 0.46, 6, 0.05 greater than p less than 0.01). This suggests that the serum level of ECP, or the "releasibility" of ECP from eosinophils, may reflect the activation of eosinophils.