Eosinophils are multifunctional proinflammatory leukocytes implicated in the pathogenesis of numerous inflammatory processes, especially allergic disorders (Gleich and Adolphson, 1986; Weller, 1991); in addition, it has been recently recognized that eosinophils may have a physiological role in organ morphogenesis (eg, postgestational mammary gland development)(Gouon-Evans et al., 2000). Eosinophils express numerous receptors (for cytokines, immunoglobulin, and complement proteins) that when engaged lead to eosinophil activation, resulting in several processes, including the release of toxic secondary granule proteins (Fig. 1)(Rothenberg, 1998). The secondary granule contains a crystalloid core composed of major basic protein (MBP) and a granule matrix which is mainly composed of eosinophil cationic protein (ECP), eosinophil-derived neurotoxin (EDN), and eosinophil peroxidase (EPO). These proteins elicit potent cytotoxic effects on a variety of host tissues at concentrations similar to those found in biological fluid from patients with eosinophilia. The cytotoxic effects of eosinophils may be elicited through multiple mechanisms, including degrading cellular ribonucleic acid, since ECP and EDN have substantial functional and structural homology to a large family of ribonuclease genes (Rosenberg et al., 1995; Slifman et al., 1986). ECP also inserts ion-nonselective pores into the membranes of target cells, which may allow the entry of the cytotoxic proteins (Young et al., 1986). Further proinflammatory damage is caused by the generation of unstable oxygen radicals formed by the respiratory burst oxidase apparatus and EPO. Furthermore, direct degranulation of mast cells and basophils is triggered by MBP. In addition to being cytotoxic, MBP directly increases smooth muscle reactivity by causing dysfunction of vagal muscarinic M2 receptors (Jacoby et al., 1993). Activation of eosinophils also leads to the generation of large amounts of leukotriene (LT) C4, which induces increased vascular permeability, mucous secretion, and smooth muscle constriction (Lewis et al., 1990). Additionally, activated eosinophils generate a wide range of cytokines, including interleukin (IL)-1, IL-3, IL-4, IL-5, IL-13, GM-CSF, TGF-/, TNF-, RANTES, macrophage inflammatory protein (MIP)-1, vasoactive intestinal