ABSTRACT
The eosinophil granulocyte is produced in the bone marrow with a production rate of 1010 and 10n eosinophils per day. Most eosinophils enter the tissues and stay there for several days to weeks and the eosinophil should probably be regarded as a tissue cell (1). Production of eosinophils is regulated by growth factors such as the interleukins 3 (IL-3) and 5 (IL-5) and the granulo cyte-macrophage-colony stimulating factor (GM-CSF). The same cytokines are also important activators of mature eosinophils and probably regulate their attraction to and accumulation in tissues. The view of the biological role of the human eosinophil has dramatically changed in the last decades and focused on the cell being a proinflammatory cell with potent cytotoxic capabilities. Findings during recent years have suggested that the eosinophil also may be active in tissue repair processes, as activated eosinophils are commonly found in fibrotic diseases. It is, however, still an open question whether the activities
of the eosinophil are responsible for the basal membrane thickening in the bronchi that is so typically observed in patients with bronchial asthma. This chapter will briefly review some important aspects of the biochemistry and function of the human eosinophil and discuss the evidence and possible role of this cell in tissue remodeling
The eosinophil is primarily a secretory cell (2). The biological activities ex erted by the eosinophil are related to the biological activities of the products produced by and released from the cell. The preformed mediators are stored in the granules of the eosinophil. The four major proteins of eosinophil gran ules are eosinophil cationic protein (ECP), eosinophil peroxidase (EPO), eo sinophil protein x/eosinophil-derived neurotoxin (EPX/EDN), and major ba sic protein (MBP). One characteristic of the four proteins is their extremely high cationic charge, which makes them very sticky. The granules also contain a number of other protein molecules of which the family of cytokines is of considerable interest. Some of these cytokines are IL-2, IL-6, IL-8, TGF-a, TGF-Pl, and GM-CSF. In addition, the human eosinophil contains in its gran ules certain enzymes with collagenolytic activities, i.e., MMP-3, also called stromelysin, and MMP-9, also called 92-kDa collagenase IV (3), and also other enzymatic activities such as an arylsulfatase B, histaminase, and phos pholipase activities (1).
