Leukotriene d(4) and interleukin-13 cooperate to increase the release of eotaxin-3 by airway epithelial cells

Introduction

Airway epithelial cells play a central role in the physiopathology of asthma. They release eotaxins when treated with T_H2 cytokines such as interleukin (IL)-4 or IL-13, and these chemokines attract eosinophils and potentiate the biosynthesis of cysteinyl leukotrienes (cysLTs), which in turn induce bronchoconstriction and mucus secretion. These effects of cysLTs mainly mediated by CysLT₁ and CysLT₂ receptors on epithelial cell functions remain largely undefined. Because the release of inflammatory cytokines, eotaxins, and cysLTs occur relatively at the same time and location in the lung tissue, we hypothesized that they regulate inflammation cooperatively rather than redundantly. We therefore investigated whether cysLTs and the T_H2 cytokines would act in concert to augment the release of eotaxins by airway epithelial cells.

Methods

A549 cells or human primary bronchial epithelial cells were incubated with or without IL-4, IL-13, and/or LTD₄. The release of eotaxin-3 and the expression of cysLT receptors were assessed by ELISA, RT-PCR, and flow cytometry, respectively.

Results

IL-4 and IL-13 induced the release of eotaxin-3 by airway epithelial cells. LTD₄ weakly induced the release of eotaxin-3 but clearly potentiated the IL-13-induced eotaxin-3 release. LTD₄ had no effect on IL-4-stimulated cells. Epithelial cells expressed CysLT₁ but not CysLT₂. CysLT₁ expression was increased by IL-13 but not by IL-4 and/or LTD₄. Importantly, the upregulation of CysLT₁ by IL-13 preceded eotaxin-3 release.

Conclusions

These results demonstrate a stepwise cooperation between IL-13 and LTD₄. IL-13 upregulates CysLT₁ expression and consequently the response to cysLTs This results in an increased release of eotaxin-3 by epithelial cells which at its turn increases the recruitment of leukocytes and their biosynthesis of cysLTs. This positive amplification loop involving epithelial cells and leukocytes could be implicated in the recruitment of eosinophils observed in asthmatics.