Measurements of ECP in serum and the impact of plasma coagulation

Serum measurement of ECP (eosinophil cationic protein) is used as an indica tion of eosinophil activation in diseases such as asthma. The levels are de pendent on sample handling, since a certain amount of ECP is released durin g 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 ill EDTA plasma and serum at 22 and 37 degrees C from healthy individuals and patients with as thma and allergy. The serum levels of ECP increased with temperature. Recal cification of citrated plasma in the presence of granulocytes with increasi ng concentrations of Ca2+ showed a dissociation between the levels of ECP a nd 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 leve ls. Incubations of granulocytes with fresh or frozen plasma and Ca2+ sugges ted the existence of a freezing labile factor in plasma, necessary for the degranulation of healthy eosinophils, but not for allregic/asthmatic eosino phils. Further experiments with pure eosinophils indicated the existence of factors in serum and plasma which facilitate ECP secretion of an active, t emperature-dependent nature. We conclude that the raised ECP levels in seru m, as compared to EDTA plasma, are unrelated to the coagulation process, bu t are due to the continuous secretion ex vivo of ECP from active eosinophil s. This process is time and temperature dependent and may be facilitated by eosinophil-activating components in the extracellular environment.