br Introduction The allergic response is a complex process
Introduction The allergic response is a complex process involving the interaction of several mediators; among these, cysteinyl leukotrienes (CysLTs) represent one of the most important actors in the pathogenesis of airway allergic diseases such as allergic rhinitis and asthma . Pharmacological studies using CysLTs indicate that two classes of receptor exist: CysLT1 receptor (CysLT1R) and CysLT2 receptor (CysLT2R) . The involvement of CysLTs in eosinophil influx is an in vivo phenomenon that was first demonstrated in guinea pigs . The inhalation of CysLTs results in a rise in sputum eosinophil counts within a few hours . CysLT1R antagonists inhibit eosinophil recruitment during airway allergic inflammation , suggesting that CysLT1R may play important roles in allergic eosinophilic inflammation. However, it is not clear whether CysLTs induce eosinophilic migration in vitro. Nagy et al. reported that neither leukotriene C4 (LTC4) nor leukotriene D4 (LTD4) caused chemotaxis of eosinophils . However, Spada et al. reported contradictory findings, showing that CysLTs elicit chemotactic activity in eosinophils . To date, studies of eosinophils have been hindered by the small number of cells that may be obtained from the peripheral blood of healthy donors, and the inability to expand eosinophils in vitro . The human eosinophilic cell line EoL-1, represents a useful in vitro model for the study human eosinophils . It has been demonstrated that EoL-1 cells may be induced to differentiate into eosinophilic granule-containing cells in response to a number of stimuli, such as treatment with butyric 98059 receptor  and dibutyryl cyclic AMP (dbcAMP) . In the present study, we aimed to clarify the effects of CysLTs and other lipid mediators on the the induction of the human eosinophilic EoL-1cell line. Utilizing this eosinophilic leukemic cell line, we demonstrated that LTD4 induces chemotaxis in EoL-1 cells via the activation of the CysLT1 receptor.
Discussion The purification of high numbers of circulating eosinophils is challenging as these cells account for less than 5% of peripheral blood leukocytes. Human eosinophilic leukemia cell line, EoL-1 cells differentiate into mature eosinophils when exposed to n-butyrate . Therefore, the EoL-1 has been utilized to study the mechanisms underlying the development and function of eosinophils in eosinophilic allergic inflammation, e.g. during allergic rhinitis and asthma. Although IL-3, IL-5 and GM-CSF, do not themselves induce the differentiation of EoL-1 cells, the presence of these cytokines significantly augments n-butyrate-induced cell differentiation . Therefore, in the present work, both n-butyrate and cytokines (IL-3, IL-5 and GM-CSF) were utilized to induce the differentiation of EoL-1 cells. In the present study, the differentiation of EoL-1 cells induced by the addition of n-butyrate, IL-3, IL-5 and GM-CSF caused the acceleration of chemotactic activity in response to CysLTs; this was concomitant with the upregulation of the expression of CysLT1R and CysLT2R. Izumi et al. reported that the n-butyrate-induced differentiation of EoL-1 cells was associated with the induction of PAF receptor gene expression as well as the augmentation of PAF-induced increase in intracellular calcium concentrations . However, no other study on the relationship between the chemotactic activity of EoL-1 cells in response to lipid mediators and cellular differentiation has been reported. It has been shown that the cell surface expression of CRTH2 in EoL-1 cells is significantly upregulated by INF-γ and TNF-α, and that PGD2-induced EoL-1 chemotaxis is potentiated by these cytokines . The present results and these previous reports suggest that the differentiation of EoL-1 cells into mature eosinophil-like cells leads to an increase in the expression of CysLT1 receptor and chemotactic activity in response to CysLTs.