Measurements of ECP in serum and the impact of plasma coagulation

Serum measurement of ECP (eosinophil cationic protein) is used as an indication of eosinophil activation in diseases such as asthma. The levels are dependent on sample handling, since a certain amount of ECP is released during storage. The mechanisms that induce this in vitro release are not known, but are supposed to be related to the coagulation process. The aim of this study was to investigate this further. ECP was measured in EDTA plasma and serum at 22 and 37°C from healthy individuals and patients with asthma and allergy. The serum levels of ECP increased with temperature. Recalcification of citrated plasma in the presence of granulocytes with increasing concentrations of Ca2+ showed a dissociation between the levels of ECP and the occurrence of coagulation. Further experiments indicated that plasma coagulation is not of any importance for the degranulation of eosinophils, nor did the addition of platelets or mononuclear cells affect the ECP levels. Incubations of granulocytes with fresh or frozen plasma and Ca2+suggested the existence of a freezing labile factor in plasma, necessary for the degranulation of healthy eosinophils, but not for allergic/asthmatic eosinophils. Further experiments with pure eosinophils indicated the existence of factors in serum and plasma which facilitate ECP secretion of an active, temperature‐dependent nature. We conclude that the raised ECP levels in serum, as compared to EDTA plasma, are unrelated to the coagulation process, but are due to the continuous secretion ex vivo of ECP from active eosinophils. This process is time and temperature dependent and may be facilitated by eosinophil‐activating components in the extracellular environment.