IL-5 up-regulates cysteinyl leukotriene 1 receptor expression in HL-60 cells differentiated into eosinophils

The cysteinyl leukotrienes, leukotriene (LT) C-4, LTD4, and LTE4, are lipid mediators that have been implicated in the pathogenesis of Several inflammatory processes, including asthma. The human LTD4 receptor, CysLT(1)R, was recently cloned and characterized. We had previously shown that HL-60 cells differentiated toward the eosinophilic lineage (HL-60/eos) developed specific functional LTD4 receptors, The present work was undertaken to study the potential modulation of CysLT(1)R expression in HL-60/eos by IL-5, an important regulator of eosinophil function, Here, we report that IL-5 rapidly up-regulates CysLT(1)R mRNA expression, with consequently enhanced CysLT(1)R protein expression and function in HL-60/eos, CysLT(1)R mRNA expression was augmented 2- to 15-fold following treatment with IL-5 (1-20 ng/ml), The effect was seen after 2 h, was maximal by 4 h, and maintained at 8 h, Although CysLT(1)R mRNA was constitutively expressed in undifferentiated HL-60 cells, its expression was not modulated by IL-5 in the absence of differentiation. Differentiated HL-60/eos cells pretreated with IL-5 (10 ng/ml) for 24 h showed enhanced CysLT(1)R expression on the cell surface, as assessed by how cytometry using a polyclonal anti-CysLT(1)R Ab, They also showed enhanced responsiveness to LTD4, but not to LTB4 or platelet-activating factor, in terms of Ca2+ mobilization, and augmented the chemotactic response to LTD4. Our findings suggest a possible mechanism by which IL-5 can modulate eosinophil functions and particularly their responsiveness to LTD4, and thus contribute to the pathogenesis of asthma and allergic diseases.