IL-5 Up-Regulates Cysteinyl Leukotriene 1 Receptor Expression in HL-60 Cells Differentiated into Eosinophils

Abstract

The cysteinyl leukotrienes, leukotriene (LT) C₄, LTD₄, and LTE₄, are lipid mediators that have been implicated in the pathogenesis of several inflammatory processes, including asthma. The human LTD₄ receptor, CysLT₁R, 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 CysLT₁R expression in HL-60/eos by IL-5, an important regulator of eosinophil function. Here, we report that IL-5 rapidly up-regulates CysLT₁R mRNA expression, with consequently enhanced CysLT₁R protein expression and function in HL-60/eos. CysLT₁R 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 CysLT₁R 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 CysLT₁R expression on the cell surface, as assessed by flow cytometry using a polyclonal anti-CysLT₁R 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.