Processed during Secretion Eosinophil Cationic Protein (ECP) Is

The eosinophil granulocyte is an inflammatory cell involved in allergic diseases such as asthma and rhinitis. Eosinophil cationic protein (ECP) is a basic and potentially cytotoxic granule protein that is released from the eosinophil upon activation. The aim was to study secretion of molecular variants of ECP from blood eosinophils with the hypothesis that the stored noncytotoxic ECP is altered into cytotoxic species upon release from the cell. T he eosinophil granulocyte takes part in the body's natural defense against invading parasites (1), as well as in other inflammatory diseases like allergic asthma and gastroin-testinal disorders (2). Once attracted to the site of inflammation the eosinophil becomes activated and, as a result of this, secretes several tissue-toxic mediators. These are either basic and granule stored proteins (eosinophil cationic protein (ECP), 3 eosin-ophil peroxidase (EPO), eosinophil protein/eosinophil-derived neurotoxin, and major basic protein (MBP)) or reactive oxygen-free radicals (3). The eosinophil also produces a wide array of different cytokines, chemokines, and lipid mediators and is therefore, in addition to being an effector cell, thought to play an immunoregulatory role in inflammatory processes as well as taking part in tissue remodelling (4, 5). ECP is one of several highly basic proteins present in the se-cretory granules of the eosinophil. ECP belongs to the superfamily of RNases and has both cytotoxic and noncytotoxic effects. The mechanism for killing target cells is by the formation of trans-membrane pores and channels. The molecular mass of ECP can differ between 16 and 22 kDa, mainly due to glycosylations of the protein. High levels of ECP are found in body fluids of patients with allergic and other inflammatory diseases, as a sign of the involvement of the eosinophil in the process. ECP secretion is induced in vitro by secretagogues such as immunoglobulins, complement factors, and serum-opsonized particles (6, 7). Blood eosinophils from allergic subjects are primed in vivo during allergen challenge, giving rise to increased migratory responses (8), adhesiveness (9), degranulation (10), and an altered oxidative metabolism (11, 12). In a previous study we showed that eosinophil extracts from healthy blood donors contain several variants of ECP with molecular masses ranging from 15.9 to 17.2 kDa when analyzed by means of a sensitive and specific surface-enhanced laser desorp-tion/ionization-time of flight mass spectrometry (SELDI-TOF MS) technique (13). Preliminary in vitro studies of fractionated ECP, purified from buffy coats, demonstrated that only some of these molecular variants displayed cytotoxic activity. …