Regulation of the release of eosinophil cationic protein by eosinophil adhesion

BACKGROUND: Varying release of eosinophil granule proteins depending on the stimulus and environmental factors has previously been reported. OBJECTIVE: To investigate the degranulation from adherent eosinophils by using mixed granulocytes. METHODS: Granulocytes isolated by Percoll gradient centrifugation were incubated on plates coated with plasma and tissue fibronectin, fibrinogen or human serum albumin (HSA) and stimulated with Mn2+, phorbol-myristate-acetate (PMA), formyl-methionyl-leucyl-phenylalanine (f-MLP) and combinations thereof, respectively. The release of eosinophil cationic protein (ECP) was measured by radioimmunoassay. RESULTS: Unstimulated eosinophils incubated in wells coated with plasma and tissue fibronectin, fibrinogen or HSA did not release any ECP. Furthermore, Mn2+ (5 mmol/L) did not induce release of ECP despite the fact that adhesion of eosinophils to these four proteins was induced. PMA stimulated a dose-dependent release of ECP. Contemporaneous stimulation of eosinophils with PMA and Mn2+ induced a dramatically increased release of ECP regardless of which protein the eosinophils were adhering to. A small but significant release of ECP was found when eosinophils incubated on plates coated with fibrinogen and HSA were stimulated by f-MLP. Contemporaneous stimulation of eosinophils with f-MLP and Mn2+ did not induce any synergistic effect on the release of ECP. On the contrary, Mn2+ inhibited the release of ECP induced by f-MLP from eosinophils. Serum-opsonized Sephadex particles stimulated a potent increase of the release of ECP up to 12%-14% in the presence of plasma fibronectin and, in particular, fibrinogen. The kinetics of eosinophil adhesion and degranulation showed that the cellular adhesion preceded the degranulation response and that the degranulation patterns depend on the stimuli and environment. CONCLUSION: The present study indicated that cellular adhesion plays an important role in the regulation of eosinophil degranulation, but that adhesion and degranulation can be induced separately.